Electrophilic substitution with rearrangement. Part VI. Bromination of 3-acetoxycholesta-3,5-diene

Abstract

Knowledge of the range of conditions and reagents through which 3-acetoxycholesta-3,5-diene (1) is brominated to give 6β-bromocholest-4-en-3-one has been extended. Intermediate adducts involving the 5,6-double bond have been shown to be components of the reaction mixture from (1) and bromine in acetic acid. Acid-catalysed isomerisation and rearrangements of the kinetically controlled products, and dibromination, can be avoided by careful choice of the conditions of bromination and work-up. Complications associated with the reaction paths have been partly elucidated. Some other sources of electrophilic bromine give smooth bromination to the 6β-bromo-derivative.