THE REDUCTIVE NAZAROV CYCLIZATION

Tri- and tetrasubstituted 1,4-dien-3-ones 1 were treated with Lewis ac id in the presence of triethylsilane, furnishing either silyl enol eth ers 4 or cyclopentanones 5 in good yields, depending upon work-up cond itions. This reaction is presumed to occur through oxyallyl intermedia te 3, which undergoes intermolecular hydride transfer and O-silylation to give 4. In most cases, only 2 equiv. of silane was required, and c atalytic amounts of Lewis acid could be used. Trienone substrate 7 was found to undergo clean conversion to tricyclic ether 8, indicating fa st capture of the oxyallyl intermediate by the pendant olefin. (C) 199 8 Elsevier Science Ltd. All rights reserved.