19-Nor and aromatic steroids. Part 1. The cleavage of 3-oxygenated-2β,19-ethers in the cholestane series

Abstract

Acetolysis of 2β,19-epoxy-5α-cholestan-3-one, catalysed by boron trifluoride, gave mainly 2α, 19-diacetoxy-5α-cholestan-3-one which was partially hydrolysed with methanolic sodium hydroxide at 20° for 10 min. to 19-acetoxy-2α-hydroxy-5α-cholestan-3-one which resisted dehydration. Acetolysis of 2β,19-epoxycholest-4-en-3-one with acetic anhydride and boron trifluoride was complicated by enolacetylation of the 3-carbonyl group and subsequent addition of acetic anhydride to the Δ-5 double bond: however, 4α-bromo-2β,19-epoxy-5α-cholestan-3-one was slowly cleaved with acetic anhydride and boron trifluoride to give only 2α,19-diacetoxy-4α-bromo-5α-cholestan-3-one which was readily converted by treatment with calcium carbonate in dimethylacetamide into 2α,19-diacetoxycholest-4-en-3-one; the latter compound was hydrolysed with methanolic hydrochloric acid to give 3-hydroxy-19-norcholesta-1,3,5(10)-triene.

3α-Acetoxy-2β,19-epoxy-5α-cholestane was cleaved with boron trifluoride in acetic anhydride, probably involving an intermediate 2α,3α-acetoxonium ion, to give mainly 3α,19-diacetoxy-5α-cholestan-2α-ol which was readily dehydrated to 3α,19-diacetoxy-5α-cholest-1-ene; this was then hydrolysed, oxidised, and decarboxylated to give 19-nor-5α-cholest-1(10)-en-3-one.