Ni-Catalyzed\nZnCl<sub>2</sub>–Assisted Domino\nCoupling of Enones and Alkyne-Tethered Vinylcyclopropanes via C–C\nBond Cleavage of Cyclopropane

A Ni-catalyzed,\nZnCl<sub>2</sub>-assisted domino coupling of enones\nand alkyne-tethered vinylcyclopropanes (VCPs) was developed. The reaction\nproceeds through the following steps: (1) oxidative cyclization of\na Ni(0) complex with an enone and the alkyne component of the alkyne-tethered\nVCP in the presence of ZnCl<sub>2</sub>, (2) carbonickelation of the\nVCP moiety, (3) β-C elimination leading to C–C bond cleavage\nof the cyclopropane moiety, and (4) β-H elimination to stereoselectively\nobtain (<i>E</i>)-1,3-diene as the coupling product. The\noptimal reaction conditions and scope of enones and alkyne-tethered\nVCPs were systematically explored. The reaction mechanism was investigated\nby performing deuterium-labeling experiments and density functional\ntheory (DFT) calculations on the model compounds. The results clarify\nthat the β-C elimination process occurs readily, and the Ni(0)\nprecatalyst is regenerated via the 1,4-addition of H–Ni(II)\nspecies, generated by β-H elimination, to an excess of enone,\nfollowed by Zn reduction of the formed 1,4-adduct.