The Experts below are selected from a list of 30 Experts worldwide ranked by ideXlab platform
Robin Polt - One of the best experts on this subject based on the ideXlab platform.
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asymmetric syntheses of 8 epi swainsonine triacetate and 1 2 di epi swainsonine carbonyl addition thwarted by an unprecedented aza pinacol rearrangement
Journal of Organic Chemistry, 2000Co-Authors: Hossein Razavi, Robin PoltAbstract:Indolizidines (-)-8-epi-swainsonine triacetate and (+)-1, 2-di-epi-swainsonine were synthesized from the O'Donnell Schiff base ester 1 derived from D-serine. Reductive-alkenylation of 1 with (i)()Bu(5)Al(2)H/H(2)C=CHMgBr followed by substrate-directed dihydroxylation of the pendant Allylic Group with OsO(4), reduction of imine, and cyclization with Ph(3)P/CCl(4) gave the polyhydroxylated pyrrolidines 8a and 8b as advanced intermediates. Efficient protecting Group manipulations converted pyrrolidines 8a and 8b to their corresponding partially protected analogues 10a and 10b, which upon Swern oxidation and diastereoselective Keck-type allylation with BF(3).Et(2)O afforded the required three-carbon homologues (10a, >20:1 de; 10b, 3.5:1 de). Use of the chelating Lewis acid MgBr(2) instead of BF(3).Et(2)O with 10a led to a novel aza-pinacol rearrangement and allylation at the alpha-carbon to yield amino alcohol 17, which is similar to a hydride migration in the biosynthetic pathway of indolizidine alkaloids. Subsequent hydroboration, cyclization, and deprotection furnished (-)-8-epi-swainsonine triacetate 15a and (+)-1,2-di-epi-swainsonine 16b in good overall yields (6.3% for 1 --> 15a, 13 steps, and 4.0% for 1 --> 16b, 14 steps).
Koichiro Oshima - One of the best experts on this subject based on the ideXlab platform.
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palladium catalyzed allylation of aryl halides with homoallyl alcohols bearing a trisubstituted double bond application to chirality transfer from hydroxylated carbon to benzylic one
ChemInform, 2010Co-Authors: Ryota Wakabayashi, Hideki Yorimitsu, Daishi Fujino, Sayuri Hayashi, Koichiro OshimaAbstract:The method allows regio- and stereoselective access to allylarenes having two substituents at the 1 and 2 position of the Allylic Group.
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transformation of zirconocene olefin complexes into zirconocene allyl hydride and their use as dual nucleophilic reagents reactions with acid chloride and 1 4 diketone
Journal of the American Chemical Society, 2004Co-Authors: Kazuya Fujita, Hideki Yorimitsu, Hiroshi Shinokubo, Koichiro OshimaAbstract:Zirconocene−olefin complexes Cp2Zr(H2CCHR), prepared in benzene−THF at 0 °C, react with acid chlorides to provide homoAllylic alcohols. The key is an equilibrium between the zirconocene−olefin complexes and the corresponding zirconocene allyl hydride complexes via Allylic C−H bond cleavage of the coordinating alkenes. Furthermore, the zirconocene−olefin complexes are also available for the reaction with 1,4-diketone to afford anti-1,4-diols with excellent diastereoselectivity. Thus, Cp2Zr(H2CCHR) serves as a donor of both hydride and an Allylic Group. These reactions also proceed efficiently by using zirconocene−olefin complexes, derived from Cp2ZrCl2, Mg metal, and 1-alkenes.
Hossein Razavi - One of the best experts on this subject based on the ideXlab platform.
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asymmetric syntheses of 8 epi swainsonine triacetate and 1 2 di epi swainsonine carbonyl addition thwarted by an unprecedented aza pinacol rearrangement
Journal of Organic Chemistry, 2000Co-Authors: Hossein Razavi, Robin PoltAbstract:Indolizidines (-)-8-epi-swainsonine triacetate and (+)-1, 2-di-epi-swainsonine were synthesized from the O'Donnell Schiff base ester 1 derived from D-serine. Reductive-alkenylation of 1 with (i)()Bu(5)Al(2)H/H(2)C=CHMgBr followed by substrate-directed dihydroxylation of the pendant Allylic Group with OsO(4), reduction of imine, and cyclization with Ph(3)P/CCl(4) gave the polyhydroxylated pyrrolidines 8a and 8b as advanced intermediates. Efficient protecting Group manipulations converted pyrrolidines 8a and 8b to their corresponding partially protected analogues 10a and 10b, which upon Swern oxidation and diastereoselective Keck-type allylation with BF(3).Et(2)O afforded the required three-carbon homologues (10a, >20:1 de; 10b, 3.5:1 de). Use of the chelating Lewis acid MgBr(2) instead of BF(3).Et(2)O with 10a led to a novel aza-pinacol rearrangement and allylation at the alpha-carbon to yield amino alcohol 17, which is similar to a hydride migration in the biosynthetic pathway of indolizidine alkaloids. Subsequent hydroboration, cyclization, and deprotection furnished (-)-8-epi-swainsonine triacetate 15a and (+)-1,2-di-epi-swainsonine 16b in good overall yields (6.3% for 1 --> 15a, 13 steps, and 4.0% for 1 --> 16b, 14 steps).
Gareth J Pritchard - One of the best experts on this subject based on the ideXlab platform.
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a comparison of the benzylic and the Allylic Group as a donor in the formal 4 2 cycloaddition to tetrahydropyrans using donor acceptor cyclobutanes
Tetrahedron Letters, 2017Co-Authors: Awais Ahmed, Steven D R Christie, Gareth J PritchardAbstract:The allyl Group was shown to be preferred over the benzyl Group as a donor in the formal [4+2]-cycloaddition reaction between a donor-acceptor cyclobutane and various aldehydes to give tetrahydropyrans.
Martin Wills - One of the best experts on this subject based on the ideXlab platform.
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Palladium-catalyzed Tandem Reactions to Form 1-vinyl-1h-isochromene Derivatives
Journal of Organic Chemistry, 2001Co-Authors: Roger Mutter, Ian B. Campbell, Eva M. Martin De La Nava, And Andy T. Merritt, Martin WillsAbstract:The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the Allylic system. The use of a lithium diamide base appears to be essential for success. The tert-butyldimethylsilyl protecting Group is also an essential choice as it furnishes the appropriate reactivity to promote Allylic substitution after the aryl coupling process. The use of more effective leaving Groups, such as acetate, results in reaction of the Allylic Group, and no aryl coupling is observed. Through the appropriate selection of phosphine ligand and solvent, either the cyclized isochromene product or the noncyclized intermediate may be formed selectively. A short combinatorial study of the scope and limitations of the reaction, involving 24 ketones, is described.