Ni-Catalyzed ZnCl2–Assisted Domino Coupling of Enones and Alkyne-Tethered Vinylcyclopropanes via C–C Bond Cleavage of Cyclopropane

A Ni-catalyzed, ZnCl2-assisted domino coupling of enones and alkyne-tethered vinylcyclopropanes (VCPs) was developed. The reaction proceeds through the following steps: (1) oxidative cyclization of a Ni(0) complex with an enone and the alkyne component of the alkyne-tethered VCP in the presence of ZnCl2, (2) carbonickelation of the VCP moiety, (3) β-C elimination leading to C–C bond cleavage of the cyclopropane moiety, and (4) β-H elimination to stereoselectively obtain (E)-1,3-diene as the coupling product. The optimal reaction conditions and scope of enones and alkyne-tethered VCPs were systematically explored. The reaction mechanism was investigated by performing deuterium-labeling experiments and density functional theory (DFT) calculations on the model compounds. The results clarify that the β-C elimination process occurs readily, and the Ni(0) precatalyst is regenerated via the 1,4-addition of H–Ni(II) species, generated by β-H elimination, to an excess of enone, followed by Zn reduction of the formed 1,4-adduct.