A Novel Reaction for Annulation onto #alpha#,#beta#-Unsaturated Ketones: W(CO)_5L Promoted Exo- and Endo-Selective Cyclizations of #omega#-Acetylenic Silyl Enol Ethers Prepared by 1,4-Addition of Propargyl Malonate to Enones

摘要

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)_5L-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.