Reaction Mechanism via a 1,2-Oxasiletanide

Reaction Mechanism of the Addition Step of an a-Silyl Carbanion to a Carbonyl Compound 

Peterson reactions of a-sUyl carbanions and carbonyl compounds leading directly to the alkenes are generally not stereoselective since the j8-hydroxyalkylsilane or yff-silylalkoxide intermediates are usually formed as a mixture of syn and anti isomers, whereas Peterson elimination from a j8-hydroxyalkylsilane proceeds in an exclusively stereospecific manner. Furthermore, the addition of an a-silyl carbanion to a carbonyl compound proceeds in an irreversible manner [29, 30]. Therefore, when the 8-hydroxyalkylsilane intermediate can neither be isolated nor separated, the diastereomeric ratio of the alkene products of the Peterson reaction is determined in the addition step of the a-silyl carbanion and the carbonyl compound. Stereospecific preparation of the y8-hydroxyalkylsilane is required for the utilization of the Peterson reaction in organic synthesis. 

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