W(CO)₅(L)-Catalyzed Formal Cope Rearrangement of Allenyl Silyl Enol Ethers

On treatment of 5-siloxyhexa-1,2,5-trienes with a catalytic amount of W(CO)₆ under photoirradiation, formal Cope rearrangement proceeded to give 2-siloxyhex-1-en-5-ynes in good yield. The electrophilic activation of the allenyl moiety by W(CO)₅ triggers the intramolecular attack of the silyl enol ether in a 6-endo manner to produce a cyclohexenyl tungsten species. Carbon−carbon bond cleavage occurs by electron donation from the anionic W(CO)₅ into the silyloxonium moiety to afford the products with regeneration of the W(CO)₅(L).