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 sigma-alkylnickel intermediates have beta-hydrogen atoms, the reaction terminates by beta-hydrogen elimination to provide cyclopentane derivatives. On the other hand, a sigma-alkylnickel intermediate that does not have beta-hydrogen atoms undergoes the insertion of a second alkene unit to cause a domino effect via a three-fold C-C bond formation process with and without the cleavage of one C-C bond.

Ring closure reactions O 0130Ni-Catalyzed, ZnCl 2 -Assisted Domino Coupling of Enones, Alkynes, and Alkenes.-A Ni(0)/ZnCl2 system effectively promotes the coupling of enones and alkene-tethered alkynes affording the corresponding coupling products with high regio-and stereoselectivity. The geometry of the products is governed by the structure of the starting enynes and also by the reaction medium, with or without Et3N and/or PPh3. Alkynes with a gem-disubstituted alkene part undergo the insertion of a second alkene unit to cause a domino effect via a three-fold C-C bond formation process with and without the cleavage of one C-C bond. Thus, the cyclopentene (XIX) bearing an alkynyl and an alkenyl moiety reacts with (V) to give a triquinane-type product (XX) in a highly stereoselective mode. -(IKEDA*, S.-I.; SANUKI, R.; MIYACHI, H.; MIYASHITA, H.; TANIGUCHI, M.; ODASHIMA, K.; J.