A chiral silyl ether as auxiliary for the asymmetric nucleophilic addition to α- and β-silyloxy carbonyl compounds
作者:Michael Trzoss、Jie Shao、Stefan Bienz
DOI:10.1016/s0040-4020(02)00553-7
日期:2002.7
Chiral silicon groups, attached as protective group in proximity to a prostereogenic functionality by means of an ether linkage, can act, at least in specific cases, efficiently as stereochemical directors. The addition of Grignard reagents to α- and β-silyloxy carbonyl compounds (silyloxy is the stereogenic (Me3C)(BnOCH2)MeSiO-group) afforded the respective products with stereofacial selectivities
Preparation of a `Si-centered' chiral auxiliary by resolution
作者:Michael Trzoss、Jie Shao、Stefan Bienz
DOI:10.1016/j.tetasy.2004.03.014
日期:2004.5
(R)- and (S)-[(benzyloxy)methyl](tert-butyl)methylsilane [(−)-(R)-1 and (+)-(S)-1], possessing a stereogenic center at the Si-atom, were prepared in highly enantiomerically enriched form by resolution via diastereomeric silyl ethers. Conversion of the hydrosilanes into different functionalized chiralsilanes by direct or stepwise substitution of the (Si)–H-atom was shown to proceed with high stereoselectivity
Chiral Acylsilanes in Organic Synthesis. Part 2. The role of the solvent, the organometallic reagent, and the nature of the substrate for the diastereoselectivity of 1,2-additions to racemic alkoxymethyl-substituted acylsilanes
作者:Alexander Chapeaurouge、Stefan Bienz
DOI:10.1002/hlca.19930760507
日期:1993.8.11
The role of the solvent, the organometallicreagent, and the nature of the substrate for the diastereoselectivity of 1,2-additions to racemicalkoxymethyl-substitutedacylsilanes was investigated with the acylsilanes 1a–d by variation of the reaction parameters. The results obtained in this study support strongly the previously proposed preferred ‘chelate-controlled’ reaction path followed under several
The treatment of alpha-silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion a-silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic-alcohol moiety followed by an acid-supported pinacol-type rearrangement, or by a sequence consisting of a pi-face-selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3). Depending on the reaction conditions, the pi-face selectivity of the oxidation step is controlled by the: stereogenic C-atom or the more remote Si-center of chirality.