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

[GRAPHICS] A highly useful method for five- and six-membered ring annulation onto alph a (1)ss -unsaturated ketones is described. 1,4-Addition of propargylmalonat e to alpha ss -unsaturated ketones in the presence of silyl triflate gives 7-siloxy-6-en-1-yne derivatives in good yield. W(CO)(5).L-catalyzed cycliza tion of these substrates can be induced to give preferentially either exo- or endo-cyclized products in good yield simply by changing the reaction sol vent.