Intramolecular and Intermolecular Lewis Acid Catalyzed Ene Reactions Using Ketones as Enophiles

Abstract

Alkylaluminum halide catalyzed intramolecular ene reactions of β-keto esters proceed in high yield to give cyclohexanols, via either a type I or type II process. Treatment of β-keto ester 3 with Me2AlCl gives cis-fused ene adduct 5 in 67 % yield. Similarly, 10 gives a 90% yield of 11 while treatment of 14 with Me3Al gives a 63% yield of 15. Treatment of 21 with Me2AlCl gives a 52% yield of a mixture of isomeric ene adducts 22 and 23. Treatment of 24 with Me1, 33AlCl1, 67 does not give the ene adduct but rather the hydrocarbon 26 which results from an unusual metathesis reaction-stepwise cycloaddition to give 25 followed by cycloreversion with loss of acetone. Intermolecular EtAlCl2-catalyzed ene reactions of ketones with reactive ene components proceed in low to moderate yield. © 1984, American Chemical Society. All rights reserved.