Abstract
1,2-Dienes (1a-e) and alkenylzirconium reagents (3a-d) underwent three-component assembly with a variety of aromatic iodides or vinyl iodide (2a-h) in the presence of NiCl2(PPh3)2, and Zn powder in dry THF at 50 □C for 24 h to furnish the corresponding 1,4-diene derivatives (4a-q) in moderate to good yields with very high regio- and stereoselectivity. In all of these three-component assembly reactions, the E isomers were formed predominantly with E/Z ratios between 94/6 to 99/1. Treatment of 7-oxa- and 7-azabenzonorbornadienes (5a-e) with various alkenylzirconium reagents (3a-h) in the presence of NiCl2(PPh3)2, and Zn powder in dry THF at 50 □C for 12 h (or a combination of ZnCl2 and NEt3) afforded the corresponding cis-2-alkenyl-1,2-dihydro naphthalene derivatives (6a-l, 7a-c) in moderate to excellent yields with high regio- and stereoselectivity. Treatment of 7-oxabenzonorbornadienes (5a-c) with various alkylzirconium reagents (15a-j) in the presence of NiBr2(dppe), and Zn powder in dry THF at 50 □C for 12 h afforded the corresponding cis-2-alkyl-1,2-dihydronaphthalene derivatives (16a-m) in good yields with high regio- and stereoselectivity. The CoI2(PPh3)2/Zn system effectively catalyzed the [2+2+2] ene-diyne cycloaddition of 1,6-heptadiynes (24a-g) with allenes (25a-e) in a highly regio- and chemoselective fashion to yield substituted benzene derivatives (27a-m, 28a-d) in good to excellent yields. Treatment of diynes (31a-g) with norbornenes (32a,b) in the presence of CoI2(PPh3)2 and Zn powder in 1,2-dichloroethane at 80 □C for 12 h afforded [2+2+2] cocyclotrimerization adduct (33a-k) exclusively in good yields. These cobalt-catalyzed results are in contrast to the ruthenium-catalyzed reaction of diyne with norbornene reported previously.