A highly efficient method for the cyclopentene annulation onto α, β-unsaturated ketones is described. Indium-mediated 1, 4-propargylation onto α, β-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.
