The chemistry of 5β,6β-epoxy-4,4-dimethylcholest-1-en-3-one. Approaches to the synthesis of 1α,5α-cyclosteroids. Part II

Abstract

Epoxidation of 4,4-dimethylcholesta-1,5-dien-3-one (9) with MCPBA gives a mixture of the corresponding epimeric 5α,6α and 5β,6β epoxides. The major product is the 5β,6β epimer 6, in contradiction to what has been reported by others. The unambiguous assignment of the structures of these epoxides is based upon NMR NOED experiments. The chemistry of the 5β,6β epoxide is described in the context of unsuccessful attempts at synthesizing the corresponding 1α,5α cyclosteroids. Reductive methods using lithium – liquid ammonia, lithium–ethylamine, or tri-n-butyl- or tri-phenyltin–AIBN gave products in which the α,β-unsaturated carbonyl system and the epoxide were reduced. When 6 was treated with BF3•etherate a B-nor derivative 27 was formed, presumably via a pinacol-type rearrangement.