Palladium-Catalyzed Ring-Opening Alkynylation of Cyclopropenones

N-Heterocyclic carbene-palladium catalysts are used to promote addition/ring opening of cyclopropenones with terminal alkynes. The ring-opening alkynylation affords alkenyl alkynyl ketones in good yields. For reactions with propargylic esters having an aryl or alkenyl substituent at the propargylic position, [3+2] annulation occurs exclusively to give 4-methylenecyclopentenones.