Pd-Catalyzed Alkyne Insertion/C–H Activation/[4 + 2] Carboannulation of Alkenes to the Synthesis of Polycyclics

An unprecedented Pd-catalyzed alkyne insertion/C–H activation/intramolecular [4 + 2] carboannulation of alkenes has been reported. In this transformation, the C–H activation was triggered by an in situ generated alkenylpalladium species via the Pd-catalyzed cross-coupling reaction of aryl iodides and alkynes. Subsequently, the resulting five-membered C, C–palladacycle intermediates were added across the alkenes, providing a unique approach to access diversified polycyclics in good efficiency. Two new rings and three C–C bonds were formed in one pot.