Use of a Semihollow-Shaped Triethynylphosphane Ligand for Efficient Formation of Six- and Seven-Membered Ring Ethers through Gold(I)-Catalyzed Cyclization of Hydroxy-Tethered Propargylic Esters

The formation of six- and seven-membered ring ethers from hydroxy-tethered propargylic esters was efficiently catalyzed by a cationic gold(I) complex with a semihollow-shaped triethynylphosphane ligand. This gold catalysis showed a tolerance toward the reactions of primary, secondary, and tertiary alcohol substrates with various substitution patterns. A sterically congested 2,2,6,6-tetraalkyl-substituted tetrahydropyran derivative as well as 6,6- and 7,6-fused bicyclic diethers were obtained in useful yields. In addition, the gold catalysis was applicable to the reaction of a sulfonamide-tethered propargylic ester to give a piperidine derivative.