Novel cyclization and reductive coupling of bicyclic olefins with alkyl propiolates catalyzed by nickel complexes*

In this article, new metal-mediated cyclization and reductive coupling reactions of bicyclic olefins with alkynes are described. Oxabicyclic alkenes undergo cyclization with alkyl propiolates at 80 °C catalyzed by nickel complexes to give benzocoumarin derivatives in high yields. The reaction of bicyclic alkenes (oxaand azacyclic alkenes) with alkyl propiolates at room temperature in the presence of the same nickel complex gave 1,2-dihydronapthelene derivatives in good-to-excellent yields. This reductive coupling reaction proceeds under very mild conditions in complete regioand stereoselective fashion. A mechanism to account for the coumarin formation and the reductive coupling is proposed.