An Efficient Method for Cyclopentene Annulation onto α,β-Unsaturated Ketones:  W(CO)₅(L)-Catalyzed 5-Endo-Dig Cyclization of 6-Siloxy-5-en-1-ynes

[reaction: see text] A highly efficient method for the cyclopentene annulation onto alpha,beta-unsaturated ketones is described. Indium-mediated 1,4-propargylation onto alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives the 6-siloxy-5-en-1-yne derivatives, which undergo W(CO)(5)(L)-catalyzed 5-endo-dig cyclization to give the corresponding cyclopentene derivatives in good yield.