Mechanistic Insight into the Nickel-Catalyzed Intermolecular [3+2+2] Cocyclization of Ethyl Cyclopropylideneacetate with Alkynes: DFT Calculations

DFT investigations were employed to explore the complete reaction mechanism of the nickel-catalyzed [3+2+2] cocyclization of ethyl cyclopropylideneacetate and alkynes. The lowest-energy pathway involves the formation of a p complex between the methylenecyclopropane moiety and the nickel atom and occurs through a sequence of ring-opening and ring-closing reactions with CC bond formation as the rate-determining step. The crucial conversion of nickelacycloheptadiene to an eight-membered nickelacycle was suggested to happen in a stepwise mechanism instead of the previously proposed cyclopropenylbutenyl rearrangement.