The reaction of an acyltrimethylsilane enolate with 2 eq of an aldehyde gives a 1:2 adduct, while that with the enolate of an α-chloroacyltrimethylsilane affords an α, β-unsaturated aldehyde as a 1:1 adduct accompanied by the carboxylic acid derived from the starting aldehyde. An oxidation-reductionreaction mechanism on the trimethylsilylcarbonyl group has been proposed.