Dicobalt octacarbonyl-catalyzed tandem cycloaddition reaction between diyne and diene under CO

Treatment of 1,7-diphenyl-1,6-heptadiyne and a symmetric butadiene such as 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene with Co(2)(CO)(8) (5 mol%) in CH(2)Cl(2) at 110 degrees C under 30 atm CO for 18 h afforded a 5.5.6 tricyclic enone in high yields. For unsymmetrical dienes such as 2-methyl-1,3-butadiene, 2-methyl-1, 3-pentadiene, and 3-methyl-1,3-pentadiene, two separable regioisomers were obtained. The catalytic reactions described are experimentally quite simple and provide a very useful synthetic procedure for the syntheses of [5.5.6] tricyclic enones.