W(CO)5(L)-catalyzed 6-endo-selective cyclization and formal Cope rearrangement of allenyl silyl enol ethers

On treatment of 5-siloxy-1,2,5-trienes with a catalytic amount of W(CO)6 under photoirradiation, two types of synthetically useful compounds, that is, 6-endo-cyclized products or formal Cope rearrangement products, are obtained selectively via the same intermediates simply by changing reaction conditions. In these reactions, electrophilic activation of the allene moiety is effectively achieved by coordination of W(CO)5, allowing intramolecular attack by neutral carbon nucleophiles in a 6-endo manner.