Silicon-directed nazarov cyclizations VII. Linearly-fused tricyclics

A new modification of the silicon-directed Nazarov cyclization is described which involves the cyclization of divinyl ketones incorporating an allylsilane as the control unit. The cyclizations are extremely facile with FeCl₃ or BF₃·OEt₂ as the Lewis acid. Four permutations of five- and six-membered ring substrates have been examined. In all cases the reactions are regio- and stereoslective. In the 6-5-6 (6ba) and 5-5-6 (6ba) systems the major product has the trans-anti configuration. The ability to incorporate a methyl substituent on the double bond and in the ring has been addressed.