Phosphine-Catalyzed [3+3] Annulation of Electron-Deficient Enyne-Type Propargylic Carbonates with α-Cyano Ketones

A novel phosphine-catalyzed [3+3] annulation of electron-deficient enyne-type propargylic carbonates with α-cyano ketones has been developed, giving tetrasubstituted γ-pyran derivatives in high yields. In this reaction, 1,2,3-butatriene phosphonium intermediates formed in situ acted as dielectrophilic reagents. This represents the first example of electron-deficient enyne-type propargylic carbonates being used as phosphine acceptors in phosphine catalysis.