A novel reaction for annulation onto alpha,beta-unsaturated ketones: W(CO)(5).L promoted exo- and endo-selective cyclizations of omega-acetylenic silyl enol ethers prepared by 1,4-addition of propargyl malonate to enones.

A highly useful method for five- and six-membered ring annulation onto alpha,beta-unsaturated ketones is described. 1,4-Addition of propargylmalonate to alpha,beta-unsaturated ketones in the presence of silyl triflate gives 7-siloxy-6-en-1-yne derivatives in good yield. W(CO)(5).L-catalyzed cyclization of these substrates can be induced to give preferentially either exo- or endo-cyclized products in good yield simply by changing the reaction solvent. [reaction: see text]