Steroidal α,β-epoxyketones. IV. Synthesis of the isomeric 6β-Bromo-4,5-epoxycholestan-3-ones

Abstract

6β-Bromocholest-4-en-3-one (I) was converted to 6β-bromo-4α,5-epoxy-5α-cholestan-3-one (II) with alkaline hydrogen peroxide. 5,6β-Dibromo-5α-cholestane- 3β,4β-diol (X) with alkali gave 6β-bromo-4β,5-epoxy-5β-cholestan-3β-ol (IXa), which was oxidized to non-crystalline 6β-bromo-4β,5-epoxy-5β-cholestan-3-one (XIII), characterized as the crystalline 3,3-dimethyl ketal (XIIa). Cleavage of (II) with hydrogen bromide in acetic acid gave 4,6β-dibromocholest-4-en-3-one (V) via the isomeric bromohydrins (IVa) and (IVb). Compound (XIII) yielded (V) directly. Sodium borohydride reduction of (I) gave cholesterol in high yield, while reduction with lithium tri-t-butoxyaluminium hydride afforded cholest-4-en-3-one (52%), cholesterol (30%), and cholest-4-en-6β-ol-3-one (7%).