Highly Regio- and Stereoselective Cocyclotrimerization and Linear Cotrimerization of alpha,beta-Unsaturated Carbonyl Compounds with Alkynes Catalyzed by Nickel Complexes.

Cyclic enones 2-cyclohexen-1-one (1a), 4,4-dimethyl-2-cyclohexen-1-one (1b), 2-cyclopenten-1-one (1c), and 2-cyclohepten-1-one (1d) react with octa-1,7-diyne (2) in THF in the presence of Ni(PPh3)2I2, ZnI2, and Zn powder at 62 °C to give [2 + 2 + 2] cycloaddition−dehydrogenation products 3a−d in 32−80% yields. α,β-Unsaturated lactone 5a (5,6-dihydro-2H-pyran-2-one) undergoes [2 + 2 + 2] cycloaddition with 2 to give both the corresponding cyclohexadiene product 6 (29%) and dehydrogenation product 7 (39%). Under similar reaction conditions, 3-buten-2-one reacts with 2 and various substituted hepta-1,6-diynes 9a−c to give [2 + 2 + 2] cycloaddition−dehydrogenation products 11a−d in 68−80% yields. Diphenylacetylene also reacts with 1a−d, 5a, and 2(5H)-furanone (5b) to afford the corresponding [2 + 2 + 2] cocyclotrimerization products 13a−d and 14a−b. No dehydrogenation of products 13 and 14 was observed under the reaction and workup conditions. The reactions of acrylates with alkynes catalyzed by nickel comple...