Cyclotrimerization of Terminal Alkynes Catalyzed by a Phosphine-Free Chloro(1,5-cyclooctadiene)iridium(I) Dimer and Induced by Tin(II) Chloride

The cyclotrimerization of terminal alkynes, such as ethyl propynoate, arylacetylenes, and alkylacetylenes, catalyzed by a phosphine-free chloro(1,5-cyclooctadiene)iridium(I) dimer ([IrCl(cod)](2)) between 40 degrees C and 100 degrees C in 1,4-dioxane is induced by a catalytic amount of tin(II) chloride to afford the corresponding 1,2,4-trisubstituted and/or 1,3,5-trisubstituted benzenes. Terminal alpha,omega-diynes, such as 1,6-heptadiynes, N,N-bis(2-propynyl)-p-toluenesulfonamide, and bis(1-phenyl-2-propynyl)ether, also undergo the cyclotrimerization with monoynes, such as ethyl propynoate, phenylacetylene, 1-decyne, and 1,2-diphenylacetylene, in a similar manner to produce the corresponding bicyclic benzene derivatives.