Reactions of 5-Hydroxy steroids. XIII. The acid-catalysed reactions of Cholestane-4,5-diol 4-acetates and Cholestane-4,5-diol diacetates

Abstract

The reaction of 5α-cholestane-4α,5-diol 4-acetate (lb) with sulphuric acid-acetic anhydride-acetic acid occurs almost exclusively by loss of the 6α-proton to give cholest-5-en-4a-yl acetate (3) while dehydration with thionyl chloride-pyridine occurs predominantly (c. 80%) by loss of the 6β-proton. On reaction with D2SO₄-DOAc-Ac₂O, 5α-cholestane-4β,5-diol 4-acetate (7) undergoes backbone rearrangement to give olefins (9),(10) and (11) without incorporation of deuterium and thus excludes the intermediacy of olefins and cyclopropanes in the rearrangement process. The effect of substituents on these reactions has been rationalized by consideration of the initial conformation of the C5 carbonium ion.