Clay Montmorillonite: An Efficient, Heterogeneous Catalyst for Michael Reactions of Silyl Ketene Acetals and Silyl Enol Ethers with α,β-Unsaturated Carbonyl Compounds

Abstract

Abstract The Michael addition of silyl ketene acetals to α,β-unsaturated esters (enoates) is investigated. The reaction is catalyzed by clay montmorillonite (solid acid) most effectively among various, homogeneous and heterogeneous acid promoters. The montmorillonite-catalyzed reaction has several prominent features: (1) Not only α- or β-monosubstituted acrylates but also α,β- or β,β-disubstituted acrylates are applicable. (2) The highly regioselective 1,4-addition to a polyenoate is achievable. (3) The Michael adduct can be obtained in the form of a labile silyl ketene acetal owing to a simple work-up procedure. The Michael reaction of a silyl enol ether and silyl ketene acetals with α,β-unsaturated ketones (enones) is also described.