W(CO)₅(L)-catalyzed endo-selective cyclization of allenyl silyl enol ethers: An efficient method for the cyclopentene annulation onto α,β-unsaturated ketones

(Matrix presented) Indium-mediated allenylation of α,β -unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives 6-siloxy-1,2,5-trienes, which undergo W(CO) ₅(L)-catalyzed 5-endo cyclization to give the corresponding cyclopentene derivatives in good yield. Furthermore, this novel W(CO) ₅(L)-catalyzed cyclization of allenyl silyl enol ethers proceeds in a 6-endo manner when 5-siloxy-1,2,5-trienes are employed as a substrate. In these reactions, effective electrophilic activation of allenyl compounds for attack by silyl enol ethers is achieved using a catalytic amount of W(CO) ₆.