Bioinspired Synthesis of Chiral 3,4-Dihydropyranones via S-to-O Acyl-Transfer Reactions

A bioinspired synthesis of chiral 3,4-dihydropyranones via S-to-O acyl-transfer reactions is described. Asymmetric Michael additionlactonization reactions of beta,gamma-unsaturated alpha-keto esters with thioesters are catalyzed by proline-derived urea, providing 3,4-dihydropyranones and spiro-3,4-dihydrocoumarin-fused 3',4'-dihydropyranones in high yield (up to 94%) with excellent stereoselectivities (up to >20:1 dr, 99% ee) under catalyst loadings as low as 1 mol %.