Ruthenium-Catalyzed [2 + 2 + 2] Cycloaddition of 1,6-Enynes and Unactivated Alkynes: Access to Ring-fused Cyclohexadienes

The [2+2+2] intermolecular carbocyclization reactions between 1,6-enynes and alkynes catalyzed by [RuCl-(cod)(Cp*)] (cod = 1,5-cyclooctadiene, Cp* = pentamethylcy-clopentadienyl) are reported to provide bicyclohexa-1,3-dienes. The presented reaction conditions are compatible with internal and terminal alkynes and the chemo-and re-gioselectivity issues are controlled by the presence of sub-stituents at the propargyl carbon center of the alkyne(s) partner(s).