Bromination of steroidal 3-keto-4,6-diene

The bromination reaction on 3-keto-4,6-diene steroids, via an epoxide inter mediate, with hydrobromic acid in acetic acid medium gives the correspondin g 6-bromo derivative. On the other hand, bromination with molecular bromine and subsequent dehydrobromination in an aprotic solvent and basic media af forded the unexpected 4-bromo derivative. In this work we suggest an altern ative mechanism for explaining the bromine transposition from C6 to C4.