Phosphine-Catalyzed Domino Reaction of α,β-Unsaturated Ketone and Allenoate: Stereoselective Synthesis of Polysubstituted Dihydro-2H-Pyran

A phosphine-catalyzed domino reaction of allenoate and two molecular alpha,beta-unsaturated ketone is reported. In particular, this unexpected strategy incorporates [2+4] annulation and subsequent Michael addition into one reaction, thus providing a new access to polysubstituted dihydropyran derivatives in an efficient manner. The reaction optimization outcome reveals that not only the catalyst, but also the experiment parameters including the solvent and temperature play significant roles for the synthesis of the products. This protocol represents a new reaction mode of two basic chemicals involving C-C and C-O bond-forming process. The present strategy also features the excellent stereoselectivity, broad substrate scope and atom economy.