DMAP‐Catalyzed [3+3] Annulation of Cyclopropenones with α‐Bromoketones for Synthesis of 2‐Pyrones

Abstract DMAP‐catalyzed [3+3] annulation of cyclopropenones with α‐bromoketones is described, which provides a simple and convenient synthesis of 2‐pyrones in good yields with a broad scope. The reaction features advantages of transition metal‐free conditions, readily available starting materials, and excellent regioselectivity. Experimental investigation and DFT calculations suggest a mechanism encompassing pyridium ylide‐initiated ring opening of cyclopropenones, elimination of DMAP catalyst, and final 6π‐electrocyclization.