The reactions of a variety of ester and lactone enolates with methyldiphenylchlorosilane were studied. The Cversus O-silylation, leading to the -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 -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 , -disubstituted esters give only O-silylation, but the a,«-substituted -silyl esters are readily prepared by the alkylation of the appropriate monosubstituted -silylated ester. The reaction of the lithium enolate of ethyl acetate and ierf-butyl acetate with (S)-(-)-l-naphthylphenylmethylchlorosilane showed the reaction to occur with inversion of configuration at silicon. Methylation of fert-butyl (1 -naphthylphenylmethylsilyl)acetate gave a 91:9 mixture of diastereomeric -silyl propionates, which could not be separated. It was found that only the y-lactones gave C-silylation with -valerolactone and e-caprolactone giving O-silylation.The silylation of ester or lactone enolates can occur to produce the silyl ketene acetals or the -silyl esters or lactones, all synthetically useful classes of compounds, as a result of silylation at the Oor C-terminus of the enolate

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a-Cyclohexylidene-7-butyroIactone. This material was prepared in 60% yield and showed the following properties: IR (neat) 1740 and 1655 cm"1;

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