Methyldiphenylsilylation of Ester and Lactone Enolates

Article abstract of DOI:10.1021/jo00238a029

The reactions of a variety of ester and lactone enolates with methyldiphenylchlorosilane were studied.The C-versus O-silylation, leading to the α-silyl ester or lactone and silyl ketene acetal, respectively, was studied as a function of the structure of the ester or lactone and the reaction conditions.It was found that all simple acetates are C-silylated irrespective of the steric demands of the alcohol portion of the ester.Esters that are monosubstituted in the α-position are cleanly C-silylated with the notable exceptions of ethyl phenylacetate and ethyl phenoxyacetate, both of which give mixtures of C- and O-silylation.The α,α-disubstituted esters give only O-silylation, but the α,α-substituted α-silyl esters are readily prepared by the alkylation of the appropriate monosubstituted α-silylated ester.The reaction of the lithium enolate of ethyl acetate and tert-butyl acetate with (S)-(-)-1-naphthylphenylmethylchlorosilane showed the reaction to occur with inversion of configuration at silicon.Methylation of tert-butyl (1-naphthylphenylmethylsilyl)acetate gave a 91:9 mixture of diastereomeric α-silyl propionates, which could not be separated.It was found that only the γ-lactones gave C-silylation with δ-valerolactone and ε-caprolactone giving O-silylation.