New Application of Solid Acid to Carbon–Carbon Bond Formation Reactions: Clay Montmorillonite-Catalyzed Aldol Reactions of Silyl Enol Ethers with Aldehydes and Acetals

Abstract

A new attempt of utilizing solid acid to the cross aldol reaction of silyl enol ethers with aldehydes or acetals has been investigated. Among solid acids employed, the reaction is promoted most effectively by a catalytic amount of aluminium ion-exchanged montmorillonite (Al-Mont). Simple diastereoselection is significantly sensitive to the nature of the reaction solvent used in the Al-Mont-catalyzed reaction. When the aluminium ions in Al-Mont were replaced by protons or titanium ions in order to investigate the cation effect, almost the same results were observed on simple diastereoselectivity and diastereofacial selectivity. This fact suggests that the metal cations in montmorillonite do not work as Lewis acid in the present aldol reaction. The acid catalysis of montmorillonite in the present aldol reaction is discussed in comparison with the catalytic behavior of some homogeneous acids.