Nickel/Zinc Chloride-Promoted Domino Reaction of polyenynes

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A Ni(0)/ZnCl_2 system effectively promotes the coupling of enones and alkene-tethered alkynes. In the reaction with 1,6-enynes, the oxidative cyclization of Ni(0) species on enones across the alkyne part followed by ZnCl_2-promoted cleavage generates alkenylnickel intermediates. Subsequent migratory insertion of the tethered alkene occurs with 5-exo-cyclization. When the resulting alkylnickel intermediates have β-hydrogen atoms, the reaction terminates by β-hydrogen elimination to provide cyclopentane derivatives. On the other hand, an alkylnickel intermediate that does not have β-hydrogen atoms undergoes the insertion of a second alkene unit to cause a domino effect via a three-fold C-C bond formation process.