Publishing type：Research paper (scientific journal)   Publisher：The Society of Synthetic Organic Chemistry, Japan  

DOI： 10.5059/yukigoseikyokaishi.77.1190

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tetlet.2018.12.066

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tetlet.2018.11.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.joc.8b01634

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

An improved synthesis of the AE ring segment of ciguatoxin CTX3C is described. The E ring segment was synthesized by the intramolecular reaction of allylic stannane and aldehyde with high stereoselectivity. Construction of the AE ring framework was performed by using the intramolecular allylation of α-acetoxy ether followed by ring-closing metathesis.

DOI： 10.1246/bcsj.20170390

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A convergent total synthesis of (−)-dactylolide is described. Constructing the 2,6-disubstituted exo-methylene THP moiety was achieved by the intramolecular allylation of α-acetoxy ether. The cyclization precursor was prepared from two segments, an alcohol and carboxylic acid derivatives, by esterification followed by reductive acetylation.

DOI： 10.1016/j.tetlet.2018.01.034

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Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Heterocyclic Chemistry  

DOI： 10.3987/com-18-s(t)57

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

The first total synthesis of two possible diastereomers of natural 6-chlorotetrahydrofuran acetogenin 1 has been achieved. The synthetic route features 5-exo-tet cyclization, Z selective Wittig reaction and Julia olefination for the construction of conjugated diene and enyne moieties, and stereoselective chlorination. Comparison of their 1H and 13C NMR data and specific rotation with those of the natural product elucidated the absolute configuration of natural (−)-6-chlorotetrahydrofuran acetogenin 1.

DOI： 10.1002/chem.201703234

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Hybrid molecules consisting of geraniol and butenolide were designed and synthesized by the late-stage divergent strategy. In the synthetic route, ring-closing metathesis was utilized for the construction of a butenolide moiety. A biological evaluation of the eight synthetic hybrid compounds revealed that these molecules exhibit antifouling activity against the cypris larvae of the barnacle Balanus (Amphibalanus) amphitrite with EC50 values of 0.30-1.31 μg mL-1. These results show that hybridization of the geraniol and butenolide structural motifs resulted in the enhancement of the antifouling activity.

DOI： 10.1039/c7ob01160a

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.orglett.6b00737

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Language：English   Publisher：Macmillan Publishers Limited.  

DOI： 10.1038/srep21487

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/chem.201503880

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/chem.201504863

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/chem.201503881

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Convergent synthesis of the EFGH ring segment of ciguatoxin CTX3C was investigated by using the intramolecular allylation of an alpha-chloroacetoxy ether and/or O,S-acetal, and subsequent ring-closing metathesis. A new method for the preparation of gamma-alkoxyallylstannane is also described. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2015.04.106

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.joc.5b00027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An enantio- and stereoselective synthesis of the C1-C7 fragment of enigmazole A is described. The three asymmetric centers of the molecule were constructed efficiently by using Evans chiral auxiliary protocol.

DOI： 10.3987/COM-13-12905

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The improved synthesis of the A-E ring segment of ciguatoxin CTX3C was performed via a highly convergent approach based on intramolecular allylation-RCM methodology.

DOI： 10.3987/COM-13-S(S)106

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BEILSTEIN-INSTITUT  

Symbiodinolide is a polyol marine natural product with a molecular weight of 2860. Herein, a streamlined synthesis of the C79-C97 fragment of symbiodinolide is described. In the synthetic route, a spiroacetalization, a Julia-Kocienski olefination, and a Sharpless asymmetric dihydroxylation were utilized as the key transformations.

DOI： 10.3762/bjoc.9.228

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

<p>A highly stereoselective and stereodivergent synthesis of two possible diastereomers of (-)-gummiferol was achieved, wherein the stepwise epoxidation and Cadiot-Chodkiewicz reaction were utilized for the construction of the diepoxide moiety and triacetylene part, respectively. Detailed comparison of their <sup>1</sup>H and <sup>13</sup>C NMR data and specific rotation with those of the natural product unambiguously elucidated the absolute stereostructure of gummiferol. In addition, the cytotoxic activity of the synthesized gummiferol, its stereoisomers, and its truncated analogues was evaluated, which clearly indicates that (1) the absolute configuration of the diepoxide moiety has little influence on the cytotoxic activity against human cancer cells and (2) the triacetylene unit is the crucial structural element required for exerting the cytotoxic activity.</p>

DOI： 10.1021/jo302665c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Stereoselective and parallel total syntheses of two possible diastereomers of (+)-sarcophytonolide C have been accomplished. Macrolactonization and transannular ring-closing metathesis (RCM) were the key transformations. Detailed comparisons of their H-1 and C-13 NMR data and specific rotation with those of the natural product allowed the absolute configuration of (+)-sarcophytonolide C to be determined.

DOI： 10.1021/ol400157s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Stereocontrolled synthesis of the E ring segment of ciguatoxin CTX3C was performed via the Negishi coupling of cyclic ketene acetal triflates. Transformation of 8-membered lactones to the corresponding ketene acetal triflates was found to be affected by the protective groups of the substrates.

DOI： 10.3987/COM-12-S(N)117

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Language：English   Publishing type：Research paper (scientific journal)  

Stereoselective synthesis of the C94-C104 fragment of symbiodinolide which is a polyol marine natural product with a molecular weight of 2860 has been accomplished. The synthetic route features Achmatowicz rearrangement and RuO 4-catalyzed dihydroxylation for the construction of the tetrahydropyran moiety and the dithiane addition to the aldehyde for the introduction of the side chain. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2012.06.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A convergent synthesis of the right-hand fragment of ciguatoxin CTX3C was investigated. The first and second generation stereocontrolled syntheses of the LM ring fragment were achieved via spiroacetalization as a key step, respectively. The polyether framework of the HIJKLM ring fragment was constructed in a convergent manner by using intramolecular allylation, ring-closing metathesis, and stereoselective hydrogenation to form the 36-methyl substituent as the key transformations. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2012.01.071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The HIJKLM ring system of ciguatozin CTX3C was synthesized in a convergent manner. The key steps were a conjugate addition/alkylation sequence, spiroacetalization, intramolecular allylation, ring-closing metathesis, and hydrogenation to form the 36-alpha-methyl substituent.

DOI： 10.1021/ol2019136

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Language：English   Publishing type：Research paper (scientific journal)  

Stereoselective synthesis of two possible diastereomers of (-)-gummiferol was accomplished by the stepwise epoxidation and Cadiot-Chodkiewicz reaction as the key transformations. Detailed comparison of their 1H and 13C NMR data and specific rotation with those of the natural product led to the absolute structural elucidation of (-)-gummiferol. © 2011 American Chemical Society.

DOI： 10.1021/ol201301b

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The C14-C24 fragment of symbiodinolide possessing the 17R/18R/21R absolute configuration, which was obtained as one of the degraded products of symbiodinolide, and its diastereomer possessing the 17R/18S/21R absolute stereochemistry were synthesized stereoselectively from cis-2-butene-1,4-diol, respectively. The detailed comparison of the synthetic products with the degraded product in the spectroscopic data confirmed unambiguously that the stereostructure of the C14 - C24 fragment was 17R, 18R, and 21R. © 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2010.07.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A convenient method for the stereoselective construction of angular methyl group of fuzed cyclic ethers is described. Reactions of mixed thioacetals with Me(2)Zn/Zn(OTO)(2) afforded the corresponding methylated products in good yields. Various protective groups such as MOM ether, benzylidene acetal, TBS ether, and pivaloyl group were stable under the reaction conditions. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2010.05.109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The convergent total synthesis of brevenal, a non-toxic brevetoxin antagonist, has been achieved. The ABC ring segment and the E ring precursor were connected by the intramolecular allylation followed by ring-closing metathesis to furnish the pentacyclic ether compound. An alternative route to the key synthetic intermediate, a pentacyclic ether core, was also examined. The right- and left-hand side chains were introduced by Wittig and Horner-Wadsworth-Emmons reactions, respectively, to furnish brevenal (1). (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2010.05.069

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Symbiodinolide is a polyol macrolide isolated from the marine dinoflagellate Symbiodinium sp. in 2007. The C14-C24 fragment of symbiodinolide possessing the 17R/18R/21R absolute configuration, which was obtained as one of the degraded products of symbiodinolide, was synthesized stereoselectively from cis-2-butene-1,4-diol. The detailed comparison of the synthetic product with the degraded product in the spectroscopic data confirmed that the stereostructure of the C14-C24 fragment was 17R, 18R, and 21R. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2010.03.014

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Language：Japanese   Publisher：Symposium on the chemistry of natural products  

Brevenal (1), a new family of marine polycyclic ether, was isolated from the Florida red tide dinoflagellate Karenia brevis by Baden and co-workers in 2004. This compound inhibits the binding of tritiated dihydrobrebetoxin-B to the voltage-sensitive sodium channels in a concentration dependent manner and acts as a nontoxic brevetoxin antagonist. Moreover, a significiant improvement of tracheal mucus velocity was observed in an animal model asthma. As well as the novel biological activities, the unique structural features have attracted attention of synthetic chemists. In 2006, the first total synthesis and structure revision of 1 were reported by Sasaki and co-workers. In this paper, we wish to report eht recent results and our efforts on the total synthesis of brevenal (1). The ABC ring segment 3 was prepared from the known compound 7 the B-alkyl Suzuki-Miyahara coupling of the phosphate 11 and the alkylborate from the iodine 5. Direct methylation of the O,S-acetal 16 was performed by using Me_2Zn/Zn(OTf)_2 in highly stereoselective manner. The ABC ring fragment obtained and the known alchol 4 were connected by our own synthetic strategy including the intramolecular allylation of α-acetoxy ether followed by ring-closing metathesis to furnish the pentacyclic ether 2. The right hand diene was introduced by the Nicolaoua's protocol. Construction of the left hand side chain, highly substituted dienyl moiety, was archieved by the modified Horner-Wadsworth-Emmons reaction with the phosphonate 33, newly developed, to afford the dienyl ether 34 as the sole product. A seris of functional transformation and deprotections of 34 furnished brevenal (1). The synthetic 1 exhiibited physical and spectroscopic data identical to those reported previously.

DOI： 10.24496/tennenyuki.51.0_223

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Cross-metathesis of methyl ester which was prepared from symbiodinolide with ethylene was performed to give the C33-C42 degraded fragment. This fragment was estimated to be (36S,40S)-diol by the modified Mosher method. Stereoselective synthesis of the (36S,40S)-diol and its diastereomer (36R,40S)-diol was achieved from L-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters which were derivatized from the (36S,40S)-diol exhibited spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded product. Thus, the absolute stereochemistry of the C33-C42 fragment was elucidated to be (36S,40S). (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2009.07.019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Stereoselective synthesis of the C1'-C25' fragment of symbiodinolide, which was obtained as a degraded product from symbiodinolide by alkaline hydrolysis, has been accomplished. The synthetic route features Kotsuki coupling and Julia-Kocienski olefination in the introduction of the side chains. This enantio-and stereoselective synthesis has established the absolute configuration of the C1'-C25' fragment.

DOI： 10.1021/jo901162v

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A convergent synthesis of the A-E ring segment of ciguatoxin CTX3C was achieved via the intramolecular allylation of an alpha-chloroacetoxy ether and subsequent ring-closing metathesis. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2009.07.037

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A useful method for the selective cleavage of primary MPM ethers by using TMSI/Et3N is described. Other protective groups such as secondary MPM ethers, silyl ethers, and benzylidene acetal were stable under the reaction conditions. (C) 2009 Elsevier Ltd. Ail rights reserved.

DOI： 10.1016/j.tetlet.2009.05.084

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(Chemical Equation Presented) Stereoselective synthesis of the C23-C34 fragment of symbiodinolide, which possesses the originally proposed stereochemistry, and its diastereomers was achieved in 19 steps from L-aspartic acid, respectively. Comparison of spectroscopic data of the synthetic products with those of the degraded product of symbiodinolide led to a structural revision of the C23-C34 fragment. © 2009 American Chemical Society.

DOI： 10.1021/jo900546k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A total synthesis of brevenal is described. The pentacyclic ether core was constructed by the intramolecular allylation of alpha-acetoxy ether and subsequent ring-closing metathesis. Both of the diene side chains were introduced by Wittig olefination and a Horner-Wadsworth-Emmons reaction, respectively, in a highly stereoselective manner.

DOI： 10.1021/ol900769d

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Symbiodinolide (1) is a polyol macrolide with a molecular weight of 2859 mu. As one of the degradation reactions, cross-metathesis of 2, which is a methyl ester of 1, with ethylene was performed to give the C33-C42 degraded fragment 4. The absolute configuration of 4 was estimated to be (36S,40S) by Mosher method. Stereoselective synthesis of 4 was achieved in 14 steps from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters exhibited the spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded fragment 4. Thus, the absolute stereochemistry of 4 was elucidated to be (36S,40S). © 2009.

DOI： 10.1016/j.tetlet.2008.11.056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The transannular Diels-Alder (TADA) reaction was applied to the synthesis of the CDE ring system of nakiterpiosin (1). TADA product 28 is a key intermediate toward the total synthesis of 1.

DOI： 10.3987/COM-08-S(F)26

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The stereoselective synthesis of the C79-C96 fragment of symbiodinolide is described in which the spiroacetalization and Kotsuki coupling are the key steps. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2008.05.078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Synthesis of the AB ring segments of ciguatoxin is described. The present synthesis includes a Lewis acid mediated cyclization of allylstannane with aldehyde, cross-metathesis reaction introducing the side chain, and Grieco-Nishizawa dehydration on the A ring. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2008.03.145

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The MgBr2-OEt2-mediated intramolecular allylation of a 4:1 diastereoisomeric mixture of the alpha-chloroacetoxyl ether la bearing the A-G/JK ring system of brevetoxin B in CH2Cl2 gave a 1: 1 diastereoisomeric mixture of the trans- and cis-cyclization products 4a and 5a having the A-G/I-K ring system, while that in CH3CN afforded the trans-isomer 4a nearly as the single product. To help clarify a reason for this marked solvent effect in the cyclization of the brevetoxin B precursor, DFT computations for the starting materials, intermediates, transition states, and products were carried out. The cyclization would proceed through a carbocation intermediate 3a having sp(2) flat structure (S(N)1 type mechanism) in CH2Cl2, in which the activation energies leading to both diastereoisomers are approximately identical, while in CH3CN alkylnitrilium salts 6a would be formed through the coordination of CH3CN to the carbocation leading to an sp(3)-type intermediate in which sever steric hindrance takes place in the transition state leading to the undesired diastereoisomer. The scope of this novel solvent-controlled stereo selectivity was tested for simple compounds. In small model compounds the marked solvent dependence was absent, but the model bearing two consecutive cyclic ether rings 1b exhibited a remarkable solvent effect similar to that observed in the brevetoxin B system.

DOI： 10.1021/jo701352

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A convergent synthesis of the key synthetic intermediate of hemibrevetoxin B was achieved via the intramolecular allylation of an alpha-chloroacetoxy ether and subsequent ring-closing metathesis. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2006.11.058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A formal total synthesis of hemibrevetoxin B (1) is described. Intramolecular allylation of alpha-chloroacetoxy ether 10, prepared from carboxylic acid 11 and alcohol 12, was carried out with MgBr2 center dot OEt2 to give 27. Ring-closing metathesis of 27 furnished tetracycle 29, which was converted to a known synthetic intermediate 9, to complete a formal total synthesis of 1.

DOI： 10.3987/COM-07-S(W)39

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A stereocontrolled synthesis of the IJK ring segment of yessotoxin is described. Cyclization of 11 mediated by SmI2 gave the IJ ring system 12 as the sole product. Construction of the K ring moiety was performed by the acid catalyzed cyclization of epoxy alcohol 20 to afford the IJK ring segment in a highly stereocontrolled manner. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2006.07.027

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Language：English   Publisher：Symposium on the chemistry of natural products  

DOI： 10.24496/intnaturalprod.2006.0__P-141_

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DOI： 10.24496/intnaturalprod.2006.0__P-140_

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

An efficient synthesis of the A-G ring segment 2, a key intermediate for the total synthesis of brevetoxin B (1), was achieved in 37 steps and 5.0% overall yield. The intramolecular allylation of the O,S-acetal 22, prepared from the ABC ring segment 15 and the FG ring segment 17, was carried out using AgOTf as a Lewis acid to give the desired compound 23, predominantly. Ring-closing metathesis of 23 with the Grubbs catalyst 12 afforded the heptacyclic ether 25. Selective hydrogenation of the E ring olefin of 25 was performed by diimide reduction to afford 2.

DOI： 10.1021/jo0603025

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A convergent synthesis of the FGHI ring segment of yessotoxin was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2005.10.136

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Brevetoxin B (1), a potent neurotoxin, was isolated from the red tide organism Gymnodinium breve Davis in 1981. The unique structural features and biological activity of this molecule have attracted the attention of synthetic chemists. We have already reported the efficient method for the convergent synthesis of polycyclic ethers via the intramolecular allylation and subsequent ring-closing metathesis. Herein we report the convergent total synthesis of 1 based on our own methodology. The reaction of the bicyclic compound 9, prepared from the known compound 6, with the allylic silane 10 in the presence of TMSOTf gave the desired product 11, stereoselectively. The JK ring segment 3 was synthesized in 11 steps including one-carbon elongation from 11. Palladium-catalyzed coupling of the ketene acetal triflate 15 and the organozinc reagent 16 gave the enol ether 17, which was converted to the diene 22. The construction of the A ring via ring-closing metathesis afforded the ABC ring segment 4. The chlorosulfide 4 was treated with the alcohol 5 in the presence of AgOTf and DTBMP to give the O,S-acetal 24. Intramolecular allylation of 26 using AgOTf as a Lewis acid provided the desired product 27, stereoselectively. Chemoselective reduction of the olefinic moiety in the E ring of 29 was carried out under the condition of the diimide reduction to afford 30. The heptacyclic compound 30 was converted to the alcohol 2 in 6 steps including one-carbon elongation. The alcohol 2 and the carboxylic acid 3 were connected successfully by Yamaguchi conditions to give the ester 33. The construction of the polycyclic framework of 1 was performed via the intramolecular allylation and subsequent ring-closing metathesis to yield 38. After the TBS and TBDPS protecting groups were removed using HF・pyr, chemoselective oxidation of the allylic moiety with MnO_2 furnished brevetoxin B (1). The synthetic brevetoxin B exhibited spectroscopic data identical with those of natural brevetoxin B.

DOI： 10.24496/tennenyuki.47.0_325

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The convergent total synthesis of brevetoxin B (1) has been achieved. The intramolecular allylation of the 0,S-acetal 20, prepared from the alpha-chlorosulfide 17 and the alcohol 5, was carried out using AgOTf as a Lewis acid to give the diene 21, predominantly. Ring-closing metathesis of 21 with the Grubbs catalyst 23 afforded the hexacyclic ether 25 which was converted to the A-G ring segment 2 through several steps. The intramolecular allylation of the alpha-acetoxy ether 42, prepared from 2 and the J-K ring segment 3, followed by ring-closing metathesis provided the polycyclic ether framework 44. A series of reactions of 44, including oxidation of the A ring, deprotection of the silyl ethers, and selective oxidation of the resulting allylic alcohol, furnished 1.

DOI： 10.1021/ja051171c

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The allylation of aromatic amines with alkynes proceeded smoothly in the presence of catalytic amounts of Pd(PPh3)(4) and benzoic acid. The allylation products were obtained in high yields in a regio- and stereoselective manner. The effect of various groups on the nitrogen atom of anilines was studied. Regardless of the substituent (electron withdrawing or electron donating) on the aromatic ring, the reaction proceeded well. Various functionalities, including -CH3, -OMe, -Cl, -CN, -COOMe, -NO2 and -COCH3 were tolerated under the reaction conditions. Similarly, the allylation of alpha-aryl aldehydes proceeded well with the same level of regio- and stereoselectivity as the allylation of aromatic amines. This reaction provides the second example of the transition metal catalyzed direct alpha-allylation of aldehydes.

DOI： 10.1021/jo0485684

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Language：Japanese   Publisher：Symposium on the chemistry of natural products  

Brevetoxin B (1), a potent neurotoxin was isolated from the red tide organism Gymnodinium breve Davis in 1981. The unique structural features and biological activity of this molecule have attracted the attention of synthetic chemists. We have already reported the efficient method for the convergent synthesis of polycyclic ethers via the intramolecular allylation and subsequent ring-closing metathesis. Herein we report the convergent synthesis of the polycyclic framework of 1 based on our own methodology. The reaction of the bicyclic compound 12, prepared from the known compound 9, with the allylic silane 13 in the presence of TMSOTf gave the desired product 14, stereoselectively. The JK ring segment 6 was synthesized in 11 steps including one-carbon elongation from 14. Palladium-catalyzed coupling of the ketene acetal triflate 22, prepared from the known compound 18, and the organozinc reagent 23 gave the enol ether 24, which was converted to the BC ring segment 7. The connection of 7 and the FG ring segment 8 followed by several transformations afforded the allylic stannane 29. The partial reduction of 29 with DIBALH followed by trapping of the resulting aluminum hemiacetal with acetic anhydride provided the acetoxy ether 30. However, the yield was very low. Alternatively, the chlorosulfide 31, prepared from 26, was treated with the alcohol 8 in the presence of AgOTf to provide the O,S-acetal 32. Cyclization of 33 using AgOTf as a Lewis acid gave the desired product 34, stereoselectively. The construction of the E ring and the A ring via ring-closing metathesis afforded the ABCDEFG ring segment 5. The alcohol 5 and the carboxylic acid 6 were connected successfully by Yamaguchi conditions to give the ester 41. The construction of the polycyclic framework of 1 was performed via the intramolecular allylation and subsequent ring-closing metathesis to yield 46. Completion of the total synthesis of 1 is currently under way.

DOI： 10.24496/tennenyuki.46.0_197

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Gambierol (1) is a marine polycyclic ether isolated as a toxic constituent from cultured cells of the ciguatera causative dinoflagellate, Gambierdiscus toxicus. This compound shows toxicity against mice (LD_<50>, 50μg/kg), and the symptoms resemble those caused by ciguatoxins. The unique structural features have attracted the attention of synthetic chemist. We have already succeeded in the convergent synthesis of the CDEFG ring system (8) via the intramolecular allylation of the α-acetoxy ether 4 and subsequent ring-closing metathesis. Encouraged by this result, we started the total synthetic study of gambierol (1). Treatment of the cyclization precursor 15, prepared from the ABC ring segment 10 and FGH ring fragment 11, with MgBr_2・OEt_2 gave the desired product 9 and its C16 epimer 16 in 22% and 47% yield, respectively. The yield of 9 was improved by using monochloroacetoxy group as a leaving moiety. Thus, the reaction of 19 gave 9 and 16 in 30% and 48% yield, respectively. The diene 9 was subjected to ring-closing metathesis with 7 to give 20 in 84% yield. The octacyclic compound 20 was converted to 28 by several steps. We next examined the construction of the triene side chain. Although the Stille coupling of 29 and 30 gave the cross-coupling product 31 in an allowable yield (63%), the reaction was very slow (4 days). After unfruitful attempts, we succeeded in developping an efficient method for the stereoselective synthesis of Z-iodoolefin 33. Treatment of 32 with Zn-Cu and AcOH gave 33 as a single stereoisomer in 80% yield. As expected, the reaction of 33 and 30 was very fast. The triene 31 was obtained in 95% yield after 1.5h. Similaly, the iodoolefin 35, prepared from 28, was converted to the fully protected gambierol 36 in good yield. The final deprotection of 36 giving 1 is currently under way.

DOI： 10.24496/tennenyuki.44.0_151

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A convergent synthesis of polycyclic ethers has been achieved by the intramolecular allylation of α-acetoxy ethers and subsequent ring-closing metathesis. The carboxylic acid 2 and alcohol 3 were connected by DCC coupling to give the ester 4 in 90% yield. After deprotection of the silyloxy group, the alcohol 5 was converted to the allylic stannane 8 via the mixed acetal 7 in good yield. The ester 8 was then subjected to the Rychnovsky protocol to give the α-acetoxy ether 9 as a mixture of diastereoisomers. The cyclization precursors 10-15 were prepared in a similar manner, and the results of the cyclization are summarized in Table 1. Treatment of 9 with 4 equiv of BF_3・OEt_2 gave a 70: 30 mixture of the cyclized products 16 and 17 in 79% yield (entry 1). Similarly, the cyclization of the substrates 10-15 proceeded stereoselectively to give the desired products in good yields (entries 2-7). We next examined the ring-closing metathesis of the products 18, 20, 22, 24, 25, and 27 (Table 2). Treatment of 18 with Grubbs catalyst 29 gave the tetracyclic ether 30 in 91% yield (entry 1). Similarly, the reactions of 20, 22, and 24 proceeded smoothly to afford the corresponding polycyclic ethers 31-33 in good yields (entries 2-4). Although the reactions of 25 and 27 with 29 were unsatisfactory, the use of the more active catalyst 34 provided the desired pentacyclic ethers 35 and 36 in high yield (entries 5 and 6). Based on these results, we have started the convergent synthesis of gambierol 1 and have synthesized the ABC and FGH ring segments, 48 and 60, from 2-deoxy-D-robose as shown in Schemes 2 and 3, respectively. Further studies toward the total synthesis of gambierol are now in progress in our laboratories.

DOI： 10.24496/tennenyuki.43.0_241

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Since 1981, a number of polycyclic ethers have been isolated from marine dinoflagellates. Much attention has been paid to the synthesis of these compounds due to their unusual structures, biological activities, and the rarity in nature. Gambierol, which has a 6,6,6,6,7,6,6,7-polycyclic ether skeleton including 18 stereocenters and a triene side chain, was isolated from the cultured cells of Gambierdiscus toxicus by Yasumoto in 1993. The compound shows toxicity against mice (LD_<50> 50μg/kg), and the symptoms resemble those caused by ciguatoxins inferring the possibility that it is also implicated in ciguatera poisoning. We now report the stereocontrolled construction of the AB, E, and H ring systems of Gambierol as parts of its total synthetic study. First, synthesis of the AB ring system of gambierol was achieved from 2-deoxy-D-ribose. The key steps were the stereoselective allylation of the aldehyde 2, corresponding to the B ring, and the intramolecular hetero-Michael reaction of 5. Next, the synthesis of the E ring was accomplished from D-ribose via the intramolecular reaction of allylic stannane 24 as a key step. The undesired stereoisomer 26 formed in this reaction was converted to the desired product 33 by using DBU mediated isomerization. Finally, stereoselective synthesis of the H ring was achieved from 2-deoxy-D-ribose by using the intramolecular reaction of allylic stannane 43 as a key step. Modified Stille coupling was successfully applied for the construction of the triene side chain to give 57.

DOI： 10.24496/tennenyuki.40.0_223

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The synthetic reaction using functionalized allylstannanes is widely appreciated as one of the most useful methods for the stereocontrolled C-C bond formation. We now report the stereoselective synthesis of functionalized heterocycles via the intramolecular reaction of allylstannane with aldehyde and imine. Stereocontrolled Total Synthesis of Hemibrevetoxin B The treatment of 6 with BF_3・OEt_2 gave 7 as a sole product. Similarly, the intramolecular reaction of 13 derived from 7 proceeded smoothly to give 14. The obtained tetracycle 14 was transformed to hemibrevetoxin B (1) by several steps. Intramolecular Reaction of Imine Derivatives To extend our methodology, we next examined the intramolecular reaction with imine, because the allylation of imine has been well studied as well as that of aldehyde, and such transformation would be an efficient method for the synthesis of cyclic amine derivatives. After several fruitless attempts, we found hydrazones are suitable as a carbon-nitrogen double bond functional group for the intramolecular reaction. The Lewis acid mediated reactions of 16 and 17 gave trans isomers 18a and 19a as a sole product in high to good yields. Stereoselective Synthesis of Hydroxylated Piperidine and Pyrrolidine Derivatives The structural framework of hydroxylated nitrogen heterocycle is widely found in naturally occurring piperidine/pyrrolidine alkaloids such as (-)-desoxoprosophilline and (+)-preussin. We examined the stereoselective synthesis of β-hydroxypiperidine and pyrrolidine derivatives via the intramolecular reaction of 20 and 22. To the best of our knowledge, this is the first example of a successful use of γ-aminoallylstannane in organic synthesis.

DOI： 10.24496/tennenyuki.38.0_709

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Hemibrevetoxin B (1), isolated from cultured cells of the red tide organism Gymnodinium breve by Prasad and Shimizu in 1989, has a 6,6,7,7-tetracyclic ether skeleton and contains 10 stereocenters. Much attention has been paid to the synthesis of polycyclic ethers including hemibrevetoxin B owing to their unusual structural framework, novel functionalities, and biological activities. Recently, Nicolaou and coworkers have reported the first total synthesis of hemibrevetoxin B. We have reported stereocontrolled synthesis of the 6,6,7,7-tetracyclic ether skeleton of 1 via the intramolecular allylic tin-aldehyde (and ketone) condensation. Chain elongation to the left-hand side aldehyde from this intermediate was difficult, and therefore we utilized 2 having hydroxypropyl side chain as a starting material. The total synthesis of 1 has been accomplished via the allylic tin methodology. The 6,6-ring system 11 prepared via the modified Nicolaou method was converted to 18. Cyclization of 18 with BF_3・OEt_2, proceeded quite smoothly and stereoselectively to give 19 in 94% yield. No diastereoisomers were detected in the cyclization step. The BF_3・OEt_2 mediated cyclization of 25 prepared from 19 by usual transformation provided the 6,6,7,7 system 26 as a single stereoisomer. Oxidation followed by Grignard reaction gave methyl carbinol derivative as a 1:1 mixture of diasteroisomers. After silyl protection, the desired isomer 27 was isolated by column chromatography. Diene side chain was introduced by Wittig olefination followed by elimination to give 30. Construction of the α-methylene aldehyde moiety was achieved by Mannich reaction with Eschenmoser's salt. ^1H and ^<13>C-NMR spectra of synthetic hemibrevetoxin B(1) was identical with those of natural product.

DOI： 10.24496/tennenyuki.37.0_139

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Recently, we have developed a novel and efficient method for the synthesis of β-alkoxy cyclic ethers. This methodology is based on the intramolecular reaction of the group 14 organometallics with acetals or aldehydes. Thus, treatment of γ-alkoxyallylsilane 1 with TiCl_4-PPh_3 afforded 6-membered cyclic ether 2a as a major product along with small amounts of its cis isomer 2b (95% total yield, trans:cis=98:2). Furthermore, this cyclization reaction was applicable for the synthesis of 7- and 8- membered cyclic ethers (Table II, Scheme 1). As a next stage, we carried out the construction of 6-7-7-6 fuzed ring system 16 which is the CDEF ring skeleton of brevetoxin B(Scheme 2, 3, 4). The BF_3・OEt_2 promoted reaction of 23 derived from optically active diol 17 gave 24 in 99% yield without accompaning the formation of any other stereoisomers. The most attractive aspect of the present procedure was iterative ring construction; the repeated use of the allic tin based cyclization gave 16 in good yield.

DOI： 10.24496/tennenyuki.33.0_78

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Recently, we have developed a new and efficient method for the carbon-carbon bond forming reaction by using copper(I)-catalyzed Grignard reagents with triflates, which bear a β-oxygen fuctionality. Since those starting triflates are readily accessible from simple chiral building blocks, the procedure provides a very convenient approach to synthesize a variety of natural products in optically active forms. As an application of this methodology, we have accomplished the enantioselective syntheses of (+)-exo-brevicomin (7), one of the aggregation pheromones of bark beetles, and (5R,6S)-(-)-6-acetoxy-5-hexadecanolide (16), a major oviposition attractant pheromone of the mosquito Culex pipiens fatigans, via tosyl-triflate 6 as a common key intermediate. In both examples the use of 6 has enabled us to realize the sequential C-C bond formation in one-pot operation and hence the overall yields were considerably improved. The similar strategy could be applied to the synthesis of naturally occurring hydroxy-γ-lactone 12 (termed L-factor). As an alternative pathway, the stepwise methods towards these target molecules were also examined.

DOI： 10.24496/tennenyuki.31.0_490

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A concise synthesis of the isolaurepinnacin skeleton 6 was achieved via the intermolecular allylation of the alpha-acetoxy ether 3 followed by ring-closing metathesis. This methodology was successfully applied to the convergent synthesis of the oxocene 15, an advanced synthetic intermediate for the total synthesis of laurencin. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2004.05.045

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Polyene macrolide antibiotics are naturally occurring antifungal agents. Members of this class include amphotericin B, which has been used widely to treat systemic fungal infections. A general synthetic strategy has been devised to prepare polyol chains associated with the polyene macrolides. Cyanohydrin acetonide alkylations were used to assemble the carbon skeleton, and a simple modification of the strategy allowed an advanced intermediate to be converted to either the candidin polyol or the nystatin polyol. The candidin polyol was further elaborated to a protected candidin aglycone. This strategy will be applicable to other members of the polyene macrolide natural products.

DOI： 10.1073/pnas.0401552101

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A concise synthesis of the isolaurepinnacin skeleton 6 was achieved via the intermolecular allylation of the alpha-acetoxy ether 3 followed by ring-closing metathesis. This methodology was successfully applied to the convergent synthesis of the oxocene 15, an advanced synthetic intermediate for the total synthesis of laurencin. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2004.05.045

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

We have developed an efficient and ecochemical process for the allylation of carbon pronucleophiles with alkynes. The reaction of alkynes with various active methynes and methylenes in the presence of Pd(PPh3)(4)/acetic acid gave the corresponding allylated products in high yields and high regioselectivities. In the present catalytic system, the key is the use of carboxylic acid which dramatically enhances the rate of the reactions. One of the important features of this process is that neither a leaving group is liberated nor is a stoichiometric amount of base needed to generate the nucleophiles.

DOI： 10.1002/adsc.200404046

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We have developed an efficient and ecochemical process for the allylation of carbon pronucleophiles with alkynes. The reaction of alkynes with various active methynes and methylenes in the presence of Pd(PPh3)(4)/acetic acid gave the corresponding allylated products in high yields and high regioselectivities. In the present catalytic system, the key is the use of carboxylic acid which dramatically enhances the rate of the reactions. One of the important features of this process is that neither a leaving group is liberated nor is a stoichiometric amount of base needed to generate the nucleophiles.

DOI： 10.1002/adsc.200404046

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DOI： 10.1021/ja039774g

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DOI： 10.1021/ja039774g

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A convergent synthesis of the A-F ring segment of yessotoxin and adriatoxin was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. © 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.10.010

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A convergent synthesis of the A-F ring segment of yessotoxin and adriatoxin was achieved via the intramolecular allylation of an alpha-chloroacetoxy ether and subsequent ring-closing metathesis. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.10.010

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Treatment of the 1,1-diiodo-1-alkenes 8, prepared from the corresponding aldehydes with CI4/PPh3, with Zn-Cu/AcOH in THF-MeOH gave the (Z)-1-iodo-1-alkenes 9, selectively, in good yields. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.09.166

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Treatment of the 1,1-diiodo-1-alkenes 8, prepared from the corresponding aldehydes with CI4/PPh3, with Zn-Cu/AcOH in THF-MeOH gave the (Z)-1-iodo-1-alkenes 9, selectively, in good yields. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.09.166

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A convergent synthesis of the F-K ring segment of brevetoxin B has been achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. © 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.09.003

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A convergent synthesis of the F-K ring segment of brevetoxin B has been achieved via the intramolecular allylation of an alpha-chloroacetoxy ether and subsequent ring-closing metathesis. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2003.09.003

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The convergent total syntheses of gambierol (1) and 16-epi-gambierol (2) have been achieved. The ABC and FGH ring segments 4 and 5 were prepared from known compounds 6 and 13, respectively, by linear manners. The fragments prepared were connected by our own synthetic strategy including the intramolecular allylation of alpha-acetoxy ether followed by ring-closing metathesis to furnish the octacyclic ether 3. The diiodoalkene 45, prepared from 3, was converted to the Z-iodoalkene 50 via a novel and stereoselective hydrogenolysis followed by deprotection. Construction of the triene side chain was performed by the modified Stille coupling of 50 with the Z-vinylic stannane 41 to afford 1. The similar transformations were carried out on the epimeric octacycle 34 to give 2, which showed no toxicity against mice at the concentration of 14 mg/kg.

DOI： 10.1021/ja036984k

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The convergent total syntheses of gambierol (1) and 16-epi-gambierol (2) have been achieved. The ABC and FGH ring segments 4 and 5 were prepared from known compounds 6 and 13, respectively, by linear manners. The fragments prepared were connected by our own synthetic strategy including the intramolecular allylation of alpha-acetoxy ether followed by ring-closing metathesis to furnish the octacyclic ether 3. The diiodoalkene 45, prepared from 3, was converted to the Z-iodoalkene 50 via a novel and stereoselective hydrogenolysis followed by deprotection. Construction of the triene side chain was performed by the modified Stille coupling of 50 with the Z-vinylic stannane 41 to afford 1. The similar transformations were carried out on the epimeric octacycle 34 to give 2, which showed no toxicity against mice at the concentration of 14 mg/kg.

DOI： 10.1021/ja036984k

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DOI： 10.1021/ja028726d

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DOI： 10.1021/ja028726d

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The reaction of internal alkynes (1) with amines (2) in the presence of catalytic amount of Pd(PPh3)(4) and benzoic acid in dioxane at 100degreesC gave the allylic amines (3) in good to excellent yields. The intramolecular reaction of alkynes with tethered amino groups (4) gave 2-vinylpyrrolidines and 2-vinylpiperidines (5) in good to excellent yields.

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The reaction of internal alkynes (1) with amines (2) in the presence of catalytic amount of Pd(PPh3)(4) and benzoic acid in dioxane at 100degreesC gave the allylic amines (3) in good to excellent yields. The intramolecular reaction of alkynes with tethered amino groups (4) gave 2-vinylpyrrolidines and 2-vinylpiperidines (5) in good to excellent yields.

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The reaction of the ketene acetal triflates 9a-e and a zinc homoenolate 10 in the presence of a catalytic amount of Pd(PPh3)(4) gave the enol ethers 11a-e in good yields. The products were converted to the corresponding cyclic ethers 14a and 14b by hydroboration and lactonization. The present methodology allowed us to synthesize the DE and GH ring segment of gambierol in a concise manner. Iterative syntheses of the polycyclic ethers 26 and 32 are also described.

DOI： 10.1021/jo025566f

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The reaction of the ketene acetal triflates 9a-e and a zinc homoenolate 10 in the presence of a catalytic amount of Pd(PPh3)(4) gave the enol ethers 11a-e in good yields. The products were converted to the corresponding cyclic ethers 14a and 14b by hydroboration and lactonization. The present methodology allowed us to synthesize the DE and GH ring segment of gambierol in a concise manner. Iterative syntheses of the polycyclic ethers 26 and 32 are also described.

DOI： 10.1021/jo025566f

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The Lewis acid mediated reaction of a-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).

DOI： 10.1021/ja025523g

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The Lewis acid mediated reaction of a-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).

DOI： 10.1021/ja025523g

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Stereocontrolled syntheses of the AB and EFGH ring systems of gambierol (1) are described. The two key intermediates 3 and 55, representing the AB and EFGH ring frameworks, were prepared from 2-deoxy-D-ribose via linear sequences. Brown's asymmetric allylboration and the intramolecular hetero-Michael reaction were successfully applied to the construction of the A ring moiety. Synthesis of the EFGH ring segment 55 was achieved by the SmI2 mediated reductive cyclization, constructing the EF ring bearing two 1,3-diaxial methyl groups, and the palladium catalyzed coupling of enol triflate and zinc bishomoenolate, making the GH ring moiety. Attempted convergent approaches toward the EFGH ring framework- are also described. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4020(02)00039-X

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Stereocontrolled syntheses of the AB and EFGH ring systems of gambierol (1) are described. The two key intermediates 3 and 55, representing the AB and EFGH ring frameworks, were prepared from 2-deoxy-D-ribose via linear sequences. Brown's asymmetric allylboration and the intramolecular hetero-Michael reaction were successfully applied to the construction of the A ring moiety. Synthesis of the EFGH ring segment 55 was achieved by the SmI2 mediated reductive cyclization, constructing the EF ring bearing two 1,3-diaxial methyl groups, and the palladium catalyzed coupling of enol triflate and zinc bishomoenolate, making the GH ring moiety. Attempted convergent approaches toward the EFGH ring framework- are also described. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4020(02)00039-X

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The AB ring segment of gambierol (1) was synthesized from 2-deoxy-D-ribose in 23 steps. The key steps were Brown's asymmetric allylboration of the aldehyde 5 and the intramolecular hetero-Michael reaction of 7. © 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01204-7

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The AB ring segment of gambierol (1) was synthesized from 2-deoxy-D-ribose in 23 steps. The key steps were Brown's asymmetric allylboration of the aldehyde 5 and the intramolecular hetero-Michael reaction of 7. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01204-7

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The EFGH ring segment of gambierol was synthesized from 2-deoxy-D-ribose in 40 steps. The present synthesis includes a SmI2-mediated reductive cyclization and a Pd-catalyzed coupling of enot triflate with a zinc bis-homoenolate as key steps. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01205-9

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The reaction of the internal alkyne 1 with alcohols 2 in the presence of a catalytic amount of Pd(PPh3)(4) and benzoic acid in dioxane at 100 degreesC gave the allylic ethers 3 in good to high yields. The reaction proceeds via the palladium/benzoic acid-catalyzed isomerization of the alkyne 1 to allene 6. followed by the addition of alcohols 2 to the pi -allylpalladium intermediate 7 formed by the hydropalladation of the resulting allene 6. Furthermore. the intramolecular reaction of alkynes having a hydroxy group at the terminus of the carbon chain gave five- and six-membered cyclic ethers in good yields. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01207-2

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The reaction of the internal alkyne 1 with alcohols 2 in the presence of a catalytic amount of Pd(PPh3)(4) and benzoic acid in dioxane at 100 degreesC gave the allylic ethers 3 in good to high yields. The reaction proceeds via the palladium/benzoic acid-catalyzed isomerization of the alkyne 1 to allene 6. followed by the addition of alcohols 2 to the pi -allylpalladium intermediate 7 formed by the hydropalladation of the resulting allene 6. Furthermore. the intramolecular reaction of alkynes having a hydroxy group at the terminus of the carbon chain gave five- and six-membered cyclic ethers in good yields. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01207-2

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The EFGH ring segment of gambierol was synthesized from 2-deoxy-D-ribose in 40 steps. The present synthesis includes a SmI2-mediated reductive cyclization and a Pd-catalyzed coupling of enot triflate with a zinc bis-homoenolate as key steps. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)01205-9

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DOI： 10.1021/ja101911o

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DOI： 10.1021/ja101911o

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Concise syntheses: of the DE and GH ring segments of gambierol (1) were achieved by the palladium-catalyzed coupling of ketene acetal triflates and a zinc homoenolate, followed by the hydroboration of the resulting cyclic enol ethers and subsequent lactonization. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)00824-3

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Concise syntheses: of the DE and GH ring segments of gambierol (1) were achieved by the palladium-catalyzed coupling of ketene acetal triflates and a zinc homoenolate, followed by the hydroboration of the resulting cyclic enol ethers and subsequent lactonization. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)00824-3

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The A ring fragment of gambieric acids was stereoselectively synthesized based on an Evans' asymmetric alkylation, Brown's asymmetric crotyl-, allylboration and an intramolecular SN2 reaction. © 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)00529-9

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The J ring segment 2 of gambieric acid was synthesized stereoselectively by the coupling between the cyclic ether component 3 and the alkenyl iodide 4. The tetrahydropyran 3 was stereoselectively synthesized by the 6-endo-cyclization of a hydroxyepoxide prepared from deoxy-D-ribose. The side chain moiety 4 was prepared by the stereoselective hydrostannation of an internal alkyne. © 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)00530-5

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The J ring segment 2 of gambieric acid was synthesized stereoselectively by the coupling between the cyclic ether component 3 and the alkenyl iodide 4. The tetrahydropyran 3 was stereoselectively synthesized by the 6-endo-cyclization of a hydroxyepoxide prepared from deoxy-D-ribose. The side chain moiety 4 was prepared by the stereoselective hydrostannation of an internal alkyne. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(01)00530-5

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DOI： 10.1016/S0040-4039(01)00529-9

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A new strategy for the convergent assembly of six-membered polycyclic ether ring fragments has been developed based upon the novel reaction between vinylstannanes with triflates in the presence of a strong base. The application of the present method has allowed for a synthetic study of the EFGH ring of gambierol to be achieved. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(00)00952-7

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A new strategy for the convergent assembly of six-membered polycyclic ether ring fragments has been developed based upon the novel reaction between vinylstannanes with triflates in the presence of a strong base. The application of the present method has allowed for a synthetic study of the EFGH ring of gambierol to be achieved. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(00)00952-7

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The intramolecular Lewis acid mediated cyclization of gamma-alkoxyallylstannanes 1, 2, and 14, bearing a hydrazone group at the terminus of the carbon chain, afforded exclusively the corresponding trans beta-amino cyclic ethers 3a, 4a, and 15, respectively. The Lewis acid mediated cyclization of gamma-alkoxyallylstannane 5, having (R)-(+)-1-phenylethylamine as a chiral auxiliary, afforded exclusively traits beta-amino cyclic ether 6a with very high diastereomeric excess (de) in very high chemical yields. The asymmetric cyclization of gamma-alkoxyallylstannane with imine 7 in the presence of chiral titanium-BINOL complex 9, afforded predominantly cis beta-amino cyclic ether 8b with high enantiomeric excess tee). The chiral Lewis acid mediated cyclization of racemic compound 38 containing phenyl as a substituent afforded cis isomer 39 with very high enantiomeric excess (ee).

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The intramolecular Lewis acid mediated cyclization of gamma-alkoxyallylstannanes 1, 2, and 14, bearing a hydrazone group at the terminus of the carbon chain, afforded exclusively the corresponding trans beta-amino cyclic ethers 3a, 4a, and 15, respectively. The Lewis acid mediated cyclization of gamma-alkoxyallylstannane 5, having (R)-(+)-1-phenylethylamine as a chiral auxiliary, afforded exclusively traits beta-amino cyclic ether 6a with very high diastereomeric excess (de) in very high chemical yields. The asymmetric cyclization of gamma-alkoxyallylstannane with imine 7 in the presence of chiral titanium-BINOL complex 9, afforded predominantly cis beta-amino cyclic ether 8b with high enantiomeric excess tee). The chiral Lewis acid mediated cyclization of racemic compound 38 containing phenyl as a substituent afforded cis isomer 39 with very high enantiomeric excess (ee).

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The stereocontrolled total synthesis of hemibrevetoxin B (1) has been achieved in 56 steps and 0.75% overall yield from D-mannose. The intramolecular reaction of gamma-alkoxyallylstannane with. aldehyde is a key step for the present total synthesis. Thus, the BF3. OEt2-mediated reaction of 24 gave 6 as a sole product. We encountered difficulty in the synthesis of gamma-alkoxyallylstannane 30 from the corresponding allyl ether 29 in which the gamma-alkoxy substituent became sterically quite bulky. This problem was solved by developing the acetal cleavage method for the synthesis of gamma-alkoxyallylstannanes. The cyclization of 38 proceeded smoothly to give the key intermediate 5 in a highly stereoselective manner. Construction of the alpha-vinyl aldehyde and (Z)-diene moieties were performed using Nicolaou's protocol.

DOI： 10.1021/jo9807619

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The stereocontrolled total synthesis of hemibrevetoxin B (1) has been achieved in 56 steps and 0.75% overall yield from D-mannose. The intramolecular reaction of gamma-alkoxyallylstannane with. aldehyde is a key step for the present total synthesis. Thus, the BF3. OEt2-mediated reaction of 24 gave 6 as a sole product. We encountered difficulty in the synthesis of gamma-alkoxyallylstannane 30 from the corresponding allyl ether 29 in which the gamma-alkoxy substituent became sterically quite bulky. This problem was solved by developing the acetal cleavage method for the synthesis of gamma-alkoxyallylstannanes. The cyclization of 38 proceeded smoothly to give the key intermediate 5 in a highly stereoselective manner. Construction of the alpha-vinyl aldehyde and (Z)-diene moieties were performed using Nicolaou's protocol.

DOI： 10.1021/jo9807619

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The synthesis of the E ring of gambierol was achieved from D-ribose via the intramolecular reaction of allylstannane with an aldehyde as a key step. The undesired stereoisomer formed in this reaction was converted to the desired product by using DBU isomerization. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01311-2

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Stereoselective synthesis of the H ring of gambierol was achieved from 2-deoxy-D-ribose by using the intramolecular reaction of allylstannane with aldehyde as a key step. Mollified Stille coupling was successfully applied for the construction of the triene side chain. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01312-4

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Stereoselective synthesis of the H ring of gambierol was achieved from 2-deoxy-D-ribose by using the intramolecular reaction of allylstannane with aldehyde as a key step. Mollified Stille coupling was successfully applied for the construction of the triene side chain. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01312-4

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The synthesis of the E ring of gambierol was achieved from D-ribose via the intramolecular reaction of allylstannane with an aldehyde as a key step. The undesired stereoisomer formed in this reaction was converted to the desired product by using DBU isomerization. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01311-2

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Synthesis of the AB ring system of gambierol (1) was achieved from 2-deoxy-D-ribose. The key steps were the stereoselective allylation of the aldehyde 6, corresponding to the B ring, and the intramolecular hetero-Michael reaction of 9. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01310-0

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Synthesis of the AB ring system of gambierol (1) was achieved from 2-deoxy-D-ribose. The key steps were the stereoselective allylation of the aldehyde 6, corresponding to the B ring, and the intramolecular hetero-Michael reaction of 9. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(98)01310-0

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The Lewis acid mediated cyclization of gamma-oxygen substituted allylic stannane 1, having a chiral imine group at the terminus of the carbon chain, afforded trans beta-amino cyclic ether 2 with very high to good diastereoselectivities in high chemical yields. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0040-4039(97)10866-8

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The Lewis acid mediated cyclization of gamma-oxygen substituted allylic stannane 1, having a chiral imine group at the terminus of the carbon chain, afforded trans beta-amino cyclic ether 2 with very high to good diastereoselectivities in high chemical yields. (C) 1998 Elsevier Science Ltd. All rights reserved.

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The thermal cyclization of gamma-aminoallylstannane (8) having an aldehyde group gave beta-hydroxypyrrolidine derivative (9a) as a sole product. This methodology was applied successfully to the total synthesis of (+)-preussin.

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Asymmetric total syntheses of (+)-desoxoprosopinine and (-)-desoxoprosophylline were accomplished using L-glutamic acid as the chiral source, in which the intramolecular reaction of a gamma-aminoallylstannane with an aldehyde was used as a key step. (C) 1997 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0957-4166(97)00563-6

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Asymmetric total syntheses of (+)-desoxoprosopinine and (-)-desoxoprosophylline were accomplished using L-glutamic acid as the chiral source, in which the intramolecular reaction of a gamma-aminoallylstannane with an aldehyde was used as a key step. (C) 1997 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0957-4166(97)00563-6

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A stereoselective total synthesis of (+)-desoxoprosopinine starting from L-glutamic acid as a chiral source was accomplished in which the intramolecular reaction of γ-aminoallylstannane with aldehyde was used as a key step.

DOI： 10.1016/S0040-4039(97)01759-0

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The intramolecular cyclization of simple acyclic (gamma-alkoxyallyl)stannane aldehydes 1, 2, and 12-15 was investigated to elucidate the relationship between the geometry of the double bond of the allylstannanes, the ring size of cyclic ethers produced by the cyclization, and the procedures for promoting the cyclization. The Lewis acid-mediated cyclization of 1-2, 12-13, and 14-15 gave the trans cyclic ethers 3, 39, and 41, respectively, either predominantly or exclusively irrespective of the geometry of the double bond and of the ring size of the cyclic ethers. The relationship in the thermal cyclization of 1 and 2, which gave the 6-membered cyclic ethers 4 and 3, was straightforward; the Z isomer 1 gave the cis product 4, and the E isomer 2 afforded the trans product 3. However, the relationship in the thermal cyclization of 12 and 13 which afforded the 5-membered cyclic ethers 39 and 40 was different from that expected from the cyclization via the well-accepted cyclic transition state, as observed in the case of 1 and 2. Both the Z (12) and E (13) isomers gave the cis cyclic ether 40 either predominantly or exclusively. The protic acid-mediated (or-catalyzed) cyclization of 12-13 and 14-15 gave the trans cyclic ethers 39 and 41, respectively, regardless of the geometry of the double bonds. On the other hand, the protic acid-promoted cyclization of 1 and 2 was very strange; the Z isomer 1 gave the cis isomer 4, and the E isomer 2 afforded the trans isomer 3. The mechanisms for these cyclization reactions are proposed.

DOI： 10.1021/jo971309c

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The intramolecular cyclization of simple acyclic (gamma-alkoxyallyl)stannane aldehydes 1, 2, and 12-15 was investigated to elucidate the relationship between the geometry of the double bond of the allylstannanes, the ring size of cyclic ethers produced by the cyclization, and the procedures for promoting the cyclization. The Lewis acid-mediated cyclization of 1-2, 12-13, and 14-15 gave the trans cyclic ethers 3, 39, and 41, respectively, either predominantly or exclusively irrespective of the geometry of the double bond and of the ring size of the cyclic ethers. The relationship in the thermal cyclization of 1 and 2, which gave the 6-membered cyclic ethers 4 and 3, was straightforward; the Z isomer 1 gave the cis product 4, and the E isomer 2 afforded the trans product 3. However, the relationship in the thermal cyclization of 12 and 13 which afforded the 5-membered cyclic ethers 39 and 40 was different from that expected from the cyclization via the well-accepted cyclic transition state, as observed in the case of 1 and 2. Both the Z (12) and E (13) isomers gave the cis cyclic ether 40 either predominantly or exclusively. The protic acid-mediated (or-catalyzed) cyclization of 12-13 and 14-15 gave the trans cyclic ethers 39 and 41, respectively, regardless of the geometry of the double bonds. On the other hand, the protic acid-promoted cyclization of 1 and 2 was very strange; the Z isomer 1 gave the cis isomer 4, and the E isomer 2 afforded the trans isomer 3. The mechanisms for these cyclization reactions are proposed.

DOI： 10.1021/jo971309c

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A stereoselective total synthesis of (+)-desoxoprosopinine starting from L-glutamic acid as a chiral source was accomplished in which the intramolecular reaction of gamma-aminoallylstannane with aldehyde was used as a key step. (C) 1997 Elsevier Science Ltd.

DOI： 10.1016/S0040-4039(97)01759-0

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The synthetic reaction using functionalized allylstannanes is widely appreciated as one of the most useful methods for the stereocontrolled C-C bond formation. We now report the stereoselective synthesis of functionalized heterocycles via the intramolecular reaction of allylstannane with aldehydes and imines. The stereocontrolled total synthesis of hemibrevetoxin B was achieved by using the intramolecular reaction of gamma-alkoxyallylstannane with aldehydes. The extension of this methodology led to a new strategy for the stereoselective synthesis of alkaloids such as (+)-desoxoprosopinine and (+)-preussin.

DOI： 10.5059/yukigoseikyokaishi.55.619

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Palladium catalyzed addition of certain carbon pronucleophiles 2 to conjugated enynes 1 afforded the corresponding allenes 3 in good to excellent yields. The most reactive methynes such as methylmalononitrile 2c enabled to undergo double addition leading to alkenes 4. Catalyst optimization supported Pd-2(dba)(3) . CHC3 - dppf combination as the best system among all catalysts tested. The plausible mechanisms for these catalytic reactions were proposed. (C) 1997 Elsevier Science Ltd.

DOI： 10.1016/S0040-4020(97)00602-9

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Palladium catalyzed addition of certain carbon pronucleophiles 2 to conjugated enynes 1 afforded the corresponding allenes 3 in good to excellent yields. The most reactive methynes such as methylmalononitrile 2c enabled to undergo double addition leading to alkenes 4. Catalyst optimization supported Pd-2(dba)(3) . CHC3 - dppf combination as the best system among all catalysts tested. The plausible mechanisms for these catalytic reactions were proposed. (C) 1997 Elsevier Science Ltd.

DOI： 10.1016/S0040-4020(97)00602-9

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DOI： 10.1021/ja970339u

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DOI： 10.1021/ja970339u

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The Lewis acid mediated reactions of allenylstannanes 1 and 13 gave trans cyclic ethers 3a and 14, respectively, with high stereoselectivities. The cyclization to 7 gave trans cyclic ether 9a. The treatment of propargylstannanes 2 and 8 with Lewis acids such as SnCl4, BuSnCl3, and ZnCl2·OEt2 induced isomerization to allenylmetal species, which underwent cyclization to the corresponding 6- and 5-membered cyclic ethers 3 and 9, respectively. The stereoselectivities dependend upon the ring size and Lewis acid utilized.

DOI： 10.1016/0040-4039(96)00469-8

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The reaction of various alcohols and gamma-methoxyallylstannane 3 in the presence of a catalytic amount of CSA afforded mixed acetals in high yields. The treatment of the acetals with TMSI and HMDS produced gamma-alkoxyallylstannanes in high yields via elimination of methanol. Copyright (C) 1996 Elsevier Science Ltd

DOI： 10.1016/0040-4039(96)00493-5

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The Lewis acid mediated cyclization of gamma-oxygen substituted allylic stannanes 1, 2 and 9, bearing a hydrazone group at the terminus of the carbon chain, afforded the corresponding trans-beta-amino cyclic ethers 3a, 4a and 10, respectively, with very high diastereoselectivities in high chemical yields.

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The Lewis acid mediated reactions of allenylstannanes 1 and 13 gave trans cyclic ethers 3a and 14, respectively, with high stereoselectivities. The cyclization fo 7 gave trans cyclic ether 9a. The treatment of propargylstannanes 2 and 8 with Lewis acids such as SnCl4, BuSnCl(3), and ZnCl2 . OEt(2) induced isomerization to allenylmetal species, which underwent cyclization to the corresponding 6- and 5-membered cyclic ethers 3 and 9, respectively. The stereoselectivities depended upon the ring size and Lewis acid utilized. (C) 1996 Elsevier Science Ltd.

DOI： 10.1016/0040-4039(96)00469-8

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The Lewis acid mediated cyclization of gamma-oxygen substituted allylic stannanes 1, 2 and 9, bearing a hydrazone group at the terminus of the carbon chain, afforded the corresponding trans-beta-amino cyclic ethers 3a, 4a and 10, respectively, with very high diastereoselectivities in high chemical yields.

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The reaction of various alcohols and gamma-methoxyallylstannane 3 in the presence of a catalytic amount of CSA afforded mixed acetals in high yields. The treatment of the acetals with TMSI and HMDS produced gamma-alkoxyallylstannanes in high yields via elimination of methanol. Copyright (C) 1996 Elsevier Science Ltd

DOI： 10.1016/0040-4039(96)00493-5

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The Lewis acid mediated intramolecular reaction of gamma-aminoallylstannane 6 gave trans-beta-hydroxypiperidine derivative 7a as a major product. On the other hand, the thermal cyclization of 6 and 8 afforded cis-beta hydroxypiperidine 7b and pyrrolidine derivative 9b, respectively, with very high stereoselectivity.

DOI： 10.1016/0040-4039(96)00205-5

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The Lewis acid mediated intramolecular reaction of gamma-aminoallylstannane 6 gave trans-beta-hydroxypiperidine derivative 7a as a major product. On the other hand, the thermal cyclization of 6 and 8 afforded cis-beta hydroxypiperidine 7b and pyrrolidine derivative 9b, respectively, with very high stereoselectivity.

DOI： 10.1016/0040-4039(96)00205-5

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The total synthesis of Hemibrevetoxin B is described. A new cyclization approach, based on the Lewis acid mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin having an aldehyde group, produced the 6-6-7-7 polycyclic ether skeleton of the natural product with high stereoselectivity. The H-1 and C-13-NMR spectra of synthetic hemibrevetoxin B was identical with those of natural product.

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The total synthesis of Hemibrevetoxin B is described. A new cyclization approach, based on the Lewis acid mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin having an aldehyde group, produced the 6-6-7-7 polycyclic ether skeleton of the natural product with high stereoselectivity. The H-1 and C-13-NMR spectra of synthetic hemibrevetoxin B was identical with those of natural product.

DOI： 10.1016/0040-4039(95)01097-2

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The total synthesis of Hemibrevetoxin B is described. A new cyclization approach, based on the Lewis acid mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin having an aldehyde group, produced the 6-6-7-7 polycyclic ether skeleton of the natural product with high stereoselectivity. The H-1 and C-13-NMR spectra of synthetic hemibrevetoxin B was identical with those of natural product.

DOI： 10.1016/0040-4039(95)01097-2

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Treatment of activated imines 1 with carbonyl compounds 2 in the presence of catalytic amounts of NiCl2(PPh(3))(2) or NiBr2(PPh(3))(2) at room temperature affords imine aldol products 3 in high to good yields.

DOI： 10.1016/0040-4039(95)00912-V

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Treatment of activated imines 1 with carbonyl compounds 2 in the presence of catalytic amounts of NiCl2(PPh(3))(2) or NiBr2(PPh(3))(2) at room temperature affords imine aldol products 3 in high to good yields.

DOI： 10.1016/0040-4039(95)00912-V

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Diels-Alder reaction of (3R,5S)-5-benzoyloxy-2,2,6,6-tetramethyl-3-heptyl acrylate (TMHD-acrylate) 1 with cyclopentadiene in the presence of TiCl4-(ArnHg)(m) complexed Lewis acids gives (1R,4R,6R)-2-norbomene-6-carboxylate derivative 4 predominantly, whereas the reaction in the presence of TiCl4 alone affords its enantiomer 2 preferentially.

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(2R,3S)-3-Allyloxy-3,4,5,6-tetrahydro-2H-pyran-2-methanol was prepared in high yield from tri-O-acetyl-D-glucal, an easily available and cheap chiral source. The hydroxyl group was protected as the t-butyldiphenylsilyl ether, and the allyl group was converted to the corresponding allyl stannane via formation of allyl carbanion and subsequent trapping with tributylstannyl chloride. The gamma-alkoxy allyl stannane 1 bearing the (2R,3S)-2-[(t-butyldiphenylsilyloxy)methyl]-3,4,5,6-tetrahydro-2H-pyran-3-yloxy auxiliary at the allyl terminus was prepared by this procedure. The reaction of 1 with aldehydes in the presence of AlCl3 . OEt(2) or AlCl3 gave the corresponding syn adducts 2 with high diastereoselectivities; the ratio of syn/anti &gt; 97:3. The diastereomeric excess of the syn adducts 2, that is, the ratio 2/(2 + the (S,S) isomer of 2), varied from 85 to 94%. Removal of the protecting group of 2 gave the (R,R) diols 3. The high diastereo- and enantioselectivity in the formation of the (R,R) isomer is accounted for by an anti S'(E) transition state 18.

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(2R,3S)-3-Allyloxy-3,4,5,6-tetrahydro-2H-pyran-2-methanol was prepared in high yield from tri-O-acetyl-D-glucal, an easily available and cheap chiral source. The hydroxyl group was protected as the t-butyldiphenylsilyl ether, and the allyl group was converted to the corresponding allyl stannane via formation of allyl carbanion and subsequent trapping with tributylstannyl chloride. The gamma-alkoxy allyl stannane 1 bearing the (2R,3S)-2-[(t-butyldiphenylsilyloxy)methyl]-3,4,5,6-tetrahydro-2H-pyran-3-yloxy auxiliary at the allyl terminus was prepared by this procedure. The reaction of 1 with aldehydes in the presence of AlCl3 . OEt(2) or AlCl3 gave the corresponding syn adducts 2 with high diastereoselectivities; the ratio of syn/anti &gt; 97:3. The diastereomeric excess of the syn adducts 2, that is, the ratio 2/(2 + the (S,S) isomer of 2), varied from 85 to 94%. Removal of the protecting group of 2 gave the (R,R) diols 3. The high diastereo- and enantioselectivity in the formation of the (R,R) isomer is accounted for by an anti S'(E) transition state 18.

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Stereocontrolled synthesis of hemibrevetoxin B framework, 7,7,6,6-tetracyclic ether skeleton, has been accomplished via the intramolecular allylic tin-aldehyde (and ketone) condensation.

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Treatment of an allylic tin-bearing chiral acetal 1a with TiCl4-PPh(3) gives the (2S, 3R) isomer 2 with high diastereoselectivity (2:3 = 93:7), whereas the reaction of an allylic silane derivative 1f affords predominantly the (2R,3S) isomer 3 (2:3 = 37:63).

DOI： 10.1039/c39940001953

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Treatment of an allylic tin-bearing chiral acetal 1a with TiCl4-PPh(3) gives the (2S, 3R) isomer 2 with high diastereoselectivity (2:3 = 93:7), whereas the reaction of an allylic silane derivative 1f affords predominantly the (2R,3S) isomer 3 (2:3 = 37:63).

DOI： 10.1039/c39940001953

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Stereocontrolled synthesis of the 7,7,6,6-tetracyclic ether skeleton of the hemibrevetoxin skeleton has been accomplished via the intramolecular allylic tin-aldehyde (and ketone) condensation.

DOI： 10.1039/c39930001638

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Stereocontrolled synthesis of the 7,7,6,6-tetracyclic ether skeleton of the hemibrevetoxin skeleton has been accomplished via the intramolecular allylic tin-aldehyde (and ketone) condensation.

DOI： 10.1039/c39930001638

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Brφnsted acid catalyzed or Bu4NF-TiCl4 mediated cyclization of (Z)-ω-stannyl ether aldehyde 1a gives 2a, whereas (E)-isomer 1b affords 2b. To explain this stereochemical outcome, a push mechanism is proposed. © 1993.

DOI： 10.1016/S0040-4039(00)91783-0

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Bronsted acid catalyzed or Bu4NF-TiCl4 mediated cyclization of (Z)-omega-stannyl ether aldehyde 1a gives 2a, whereas (E)-isomer 1b affords 2b. To explain this stereochemical outcome, a push-pull mechanism is proposed.

DOI： 10.1016/S0040-4039(00)91783-0

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

Asymmetric synthesis of syn 1,2-diols 3 has been accomplished via the reaction of the chiral gamma-alkoxy-substituted allylstannane 1 with aldehydes in the presence of AlCl3 or AlCl3.OEt2, followed by a five-step operation to remove the chiral auxiliary.

DOI： 10.1021/jo00052a002

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

Asymmetric synthesis of syn 1,2-diols 3 has been accomplished via the reaction of the chiral gamma-alkoxy-substituted allylstannane 1 with aldehydes in the presence of AlCl3 or AlCl3.OEt2, followed by a five-step operation to remove the chiral auxiliary.

DOI： 10.1021/jo00052a002

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Diisopropyl Tartrate Modified (E)-gamma-[(Cyclohexyloxy)dimethylsilyl]- and (E)-gamma-(Dimethylphenylsilyl)allylboronates: Chiral Reagents for the Enantio- and Diastereoselective Synthesis of anti-1,2-Diols and 2-Butene-1,4-diols via the Formal alpha- and gamma-Hydroxyallylation of Aldehydes

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Diisopropyl Tartrate Modified (E)-gamma-[(Cyclohexyloxy)dimethylsilyl]- and (E)-gamma-(Dimethylphenylsilyl)allylboronates: Chiral Reagents for the Enantio- and Diastereoselective Synthesis of anti-1,2-Diols and 2-Butene-1,4-diols via the Formal alpha- and gamma-Hydroxyallylation of Aldehydes

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The BF3.OEt2 mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin (1) having an aldehyde group at the terminus of the carbon chain proceeded in a stereocontrolled manner to give the 7-membered beta-hydroxy cyclic ether (2a) with high diastereoselectivity. This method was applied for the synthesis of the 6.7.7.6 ring system (3a).

DOI： 10.1016/0040-4039(91)85042-4

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The BF3.OEt2 mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin (1) having an aldehyde group at the terminus of the carbon chain proceeded in a stereocontrolled manner to give the 7-membered beta-hydroxy cyclic ether (2a) with high diastereoselectivity. This method was applied for the synthesis of the 6.7.7.6 ring system (3a).

DOI： 10.1016/0040-4039(91)85042-4

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：GEORG THIEME VERLAG  

The titanium(IV) chloride-triphenylphosphine mediated intramolecular cyclization of gamma-oxo-substituted allylic silane 1 (4-[3-(trimethylsilyl)-1-propenyloxy]butanal propylene acetal) having an acetal group at the terminus of the carbon chain produced the 6-membered trans isomer 2a [trans-3-(3-hydroxypropoxy)-2-vinyltetrahydropyran] with very high diastereoselectivity in high yield. Highly stereoselective synthesis of seven-and eight-membered rings was also accomplished by the use of titanium(IV) chloride-triphenylphosphine.

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00312a003

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00312a003

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00301a038

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00301a038

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Language：English   Publisher：GEORG THIEME VERLAG  

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Language：English   Publisher：GEORG THIEME VERLAG  

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S0040-4039(00)97688-3

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S0040-4039(00)97688-3

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00282a037

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jo00282a037

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S0040-4039(00)99305-5

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DOI： 10.1016/S0040-4039(00)72737-7

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DOI： 10.1016/S0040-4039(00)99305-5

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S0040-4039(00)72737-7

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Language：English   Publisher：CHEMICAL SOC JAPAN  

DOI： 10.1246/cl.1988.927

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Language：English   Publisher：CHEMICAL SOC JAPAN  

DOI： 10.1246/cl.1988.927

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