Synthesis of 3,4-Dihydropyran-2-ones Catalyzed by Quaternary Ammonium Phenoxide

Significance

An enantioselective one-pot synthesis of 3,4-dihydropyran-2-ones 3 by tandem Michael addition and lactonization between α,β-unsaturated ketones 1 and the silyl enolate 2 derived from phenyl isobutyrate in the presence of a Lewis base catalyst (5 mol%) such as chiral quaternary ammonium phenoxide A is described. The organocatalyst A is easily prepared from cinchona alkaloids and affords 3,4-dihydropyran-2-ones 3 in high yields and enantioselectivities within only one hour. In this reaction, the phenoxy group on the silyl enolate 2 behaves as an effective leaving group to facilitate intramolecular cyclization of the in situ generated Michael adduct, and the liberated phenoxide ion acts also as a Lewis base catalyst to activate silyl enolate 2.