Enantioselective Synthesis of 3,4-Dihydropyran-2-ones by Chiral Quaternary Ammonium Phenoxide-catalyzed Tandem Michael Addition and Lactonization

Chiral quaternary ammonium phenoxides derived from cinchona alkaloids were easily synthesized and were effectively employed in the tandem Michael addition and lactonization between α,β-unsaturated ketones and a silyl enolate derived from phenyl isobutyrate, and optically active 3,4-dihydropyran-2-ones were afforded in high yields with high enantiomeric excesses.