Highly Selective Cascade C–C Bond Formation via Palladium- Catalyzed Oxidative Carbonylation–Carbocyclization–Carbonylation–Alkynylation of Enallenes

A highly efficient palladium-catalyzed oxidative cascade reaction of enallenes undergoing overall four C-C bond formations has been developed. The insertion cascade proceeds via carbonylation-carbocyclization-carbonylation-alkynylation involving sequential insertion of carbon monoxide, olefin, and carbon monoxide. Furthermore, different types of terminal alkynes and functionalized enallenes have been investigated and found to undergo the cascade reaction under mild reaction conditions.