A Novel Reaction for Annulation onto α,β-Unsaturated Ketones: W(CO)₅·L Promoted Exo- and Endo-Selective Cyclizations of ω-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]