[3 + 3] Cyclodimerization of Methylenecyclopropanes: Stoichiometric and Catalytic Reactions of Nickel(0) with Electron-Deficient Alkylidenecyclopropanes

Stoichiometric treatment of Ni(cod)2 with ethyl cyclopropylideneacetate (ECPA) in the presence of PCy3 resulted in an unpredicted formation of a Ni(0) complex bearing an (E,E)-1,2-bis(exo-alkylidene)cyclohexane ligand, which stemmed from the [3 + 3] cyclodimerization of ECPA. The reaction could be expanded to a Ni(0)-catalyzed [3 + 3] cyclodimerization reaction of ester-substituted methylenecyclopropanes, giving the corresponding cyclohexane derivatives in excellent yields.