Allylic acetoxylation of Δ5-steroids at C-4

The allylic acetoxylation of Δ5-steroids at C-4 by reaction with bromine and silver acetate has been shown to depend upon the nature of the C-3 substituent. 2H Labelling studies have shown that the reaction, which proceeds via the 5α,6β-dibromide, involves the trans diaxial elimination of a 4β-proton to form a Δ4-6β-bromide which then undergoes an SN2′ displacement by the incoming acetate assisted by the silver ion.