Catalytic Enantioselective Construction of All-Carbon Quaternary Stereocenters:  Synthetic and Mechanistic Studies of the C-Acylation of Silyl Ketene Acetals

With the aid of an appropriate chiral catalyst, acyclic silyl ketene acetals react with anhydrides to furnish 1,3-dicarbonyl compounds that bear all-carbon quaternary stereocenters in good ee and yield. Mechanistic studies provide strong support for a catalytic cycle that involves activation of both the electrophile (anhydride --> acylpyridinium) and the nucleophile (silyl ketene acetal --> enolate).