Lewis Acid Mediated Reactions of Cyclopropyl Aryl Ketones with α-Ketoesters:  Facile Preparation of 5,6-Dihydropyran-2-ones

A new general method for the synthesis of 5,6-dihydropyran-2-ones from cyclopropyl aryl ketones (monoactivated cyclopropanes) and α-ketoesters in good to excellent yields has been developed. The process involves a cascade of reactions, including a nucleophilic ring-opening reaction of monoactivated cyclopropane by H₂O, Lewis acid mediated transesterification, and an aldol type reaction.