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. The ring‐opening alkynylation of cyclopropenones with terminal alkynes is catalyzed by palladium–N‐heterocyclic carbene (NHC) complexes to provide alkenyl alkynyl ketones. In contrast, [3+2] annulation to give cyclopentenones occurs if secondary propargylic esters bearing an aryl or alkenyl substituent are used.