- Asymmetric reduction of aliphatic ketones and acyl silanes using chiral anti-pentane-2,4-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid
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Aliphatic ketones were reduced to the corresponding secondary alcohols by using anti-1,3-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid (DNBSA) in benzene at reflux. Addition of 1-octanethiol in that media improved the efficiency of the reduction. Asymmetric reduction of aliphatic ketones was performed by using chiral anti-pentane-2,4-diol, and highly asymmetric induction (up to >99% ee) was observed in the reduction of tert-alkyl ketones. Asymmetric reduction of acyl silanes using chiral anti-pentane-2,4-diol and DNBSA proceeded efficiently in the absence of octanethiol and the corresponding α-silyl alcohols were obtained in high yields with high ees.
- Matsuo, Jun-Ichi,Hattori, Yu,Hashizume, Mio,Ishibashi, Hiroyuki
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experimental part
p. 6062 - 6069
(2010/10/02)
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- Reactions of silyl-stabilised sulfur ylides with organoboranes: Enantioselectivity, mechanism, and understanding
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The reaction of trimethylsilyl-substituted sulfonium ylides with organoboranes (Ph3B, Et3B) has been studied and although homologated products were obtained in good yield (after oxidation to the corresponding alcohols), the enantiomeric excesses were low with our camphor-based chiral sulfide (up to 40% ee, cf. corresponding phenyl-substituted sulfonium ylides gave >95% ee). Cross-over experiments were conducted to ascertain the nature of this difference in selectivity. Thus, aryl- and silyl-substituted sulfonium ylides (1 equiv.) were (separately) reacted with Et3B (1.5 equiv.) followed by Ph3B (1.5 equiv.) The experiments were repeated changing the order of addition of the two boranes. It was found that the aryl-substituted sulfonium ylide only trapped the first borane that was added indicating that ate complex formation was non-reversible and so was the selectivity determining step. In contrast the silyl-substituted sulfonium ylide only trapped Ph3B (it is more reactive than Et 3B) indicating that ate complex formation was reversible and so 1,2-migration was now the selectivity determining step. The reactions have been studied computationally and the experimental observations have been reproduced. They have further revealed that the cause of reversibility in the case of the silyl-substituted sulfonium ylides results from ate complex formation being less exothermic and a higher barrier to 1,2-migration. This journal is The Royal Society of Chemistry.
- Howells, Dean,Robiette, Raphael,Fang, Guang Y.,Knowles, Luke S.,Woodrow, Michael D.,Harvey, Jeremy N.,Aggarwal, Varinder K.
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supporting information; experimental part
p. 1185 - 1189
(2008/10/09)
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- Optically pure α-(trimethylsilyl)benzyl alcohol: A practical chiral auxiliary for oxocarbenium ion reactions
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(matrix presented) Enantiopure (S)-α-(trimethylsilyl)benzyl alcohol (98% ee) was prepared by Noyori's transfer hydrogenation of benzoyltrimethylsilane. The corresponding trimethylsilyl ether was subjected to Marko's silyl modified Sakurai conditions with
- Cossrow, Jennifer,Rychnovsky, Scott D.
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p. 147 - 150
(2007/10/03)
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- Enantioselective synthesis of a-hydroxysilanes by bioreduction of aroyltrimcthylsilanes
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Aromatic acylsilanes [Ar-CO-SiMe3; Ar = C6H5,4-ClC6H4, 2-, 3- and 4-OMeC6H4, 3,4-(OMe)2C6H3 and 3,4-OCH2OC6H3] were reduced by baker's yeast to optically active a-silyl alcohols in 20-70% yield and 43-88% ee. Comments are made on the influence of silicon in this bioreduction reaction. The Royal Society of Chemistry 1999.
- Patrocinio, Amauri F.,Correa Jr., Ivan R.,Moran, Paulo J. S.
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p. 3133 - 3137
(2007/10/03)
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- Enantioselective reduction of α,β-unsaturated acylsilanes by chiral lithium amides
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(equation presented) Reaction of β-substituted acryloylsilanes I with lithium amides II affords α-silyl allylic alcohols III in high enantiomeric excess (>99percent) via formal hydride transfer from the chiral lithium amide.
- Takeda, Kei,Ohnishi, Yuji,Koizumi, Toru
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p. 237 - 239
(2008/02/12)
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