Construction of Methylenecycloheptane Frameworks through 7-Exo-Dig Cyclization of Acetylenic Silyl Enol Ethers Catalyzed by Triethynylphosphine-Gold Complex

A cationic gold(I) complex bearing a semihollow-shaped triethynylphosphine ligand efficiently catalyzed the 7-exo-dig cyclization of silyl enol ethers with an omega-alkynic substituent. The reaction gave various methylenecycloheptane derivatives with an exo- or endocyclic carbonyl group. The protocol was applicable not only to cyclic substrates that form bicyclic frameworks but also to acyclic ones with or without substituents in a carbon chain tether.