光学活性β‐シリルスルホキシドを用いた不斉反応とその応用

Abstract

Reactions of p-tolyl α-lithio-β-silylethyl sulfoxides with various electrophiles proceed with high stereoselectivity. Reactions of α-sulfinyl carbanions of the β-trimethylsilylethyl sulfoxides with aldehydes, ketones, or trimethylphosphate, give the products with high stereoselectivity. The high stereoselectivity of these reactions can be ascribed to the trialkylsilyl group at the β-position. New interaction between the silicon and the carbonyl oxygen in the transition state is demonstrated by the MO calculation. Reaction of the α-sulfinyl carbanion of the β-trimethylsilylethyl sulfoxide with α, β-unsaturated carbonyl compounds gives the conjugate addition products with extremely high stereoselectivity. The intermediate enolates are also stereoselectively trapped with various alkyl halides or aldehydes to give the corresponding products having 4 or 5 consecutive chiral centers. Intramolecular cyclization of the enolates gives chiral cycloalkanecarboxylates and this reaction opens a route to convenient synthesis of the optically pure chrysanthemate. The stereo- and regioselective elimination of the sulfinyl group is achieved by the action of the β-silyl group. It is demonstrated that acceleration of the sulfenic acid-elimination from the β-silylethenyl sulfoxide is mainly ascribed to the β-effect of the silyl group by the MO calculation. These reaction features show that p-tolyl α-lithio-β-silylethyl and p-tolyl α-lithio-β-silylethenyl sulfoxides are useful chiral vinyl and ethynyl anion synthetic equivalents, respectively.