Process for the preparation of 21-bromo-4-pregnene-3,20-dione derivatives

A process for the preparation of a 21-bromo-4-pregnene-3,20-dione compound of formula I ##STR6## wherein R.sub.1 is a hydrogen atom, a hydroxy group, or an alkanoyl group of up to 6 carbon atoms;

• R.sub.2 is a hydrogen atom or a methyl group;
• or
• R.sub.1 and R.sub.2 jointly are an isopropylidenedioxy group;
• R.sub.3 is a hydrogen atom, a fluorine atom, or a methyl group;
• V is a methylene group or ethylene group;
• X is a hydrogen atom, a fluorine atom, or a chlorine atom;
• and
• Y is a methylene group, a hydroxymethylene group, or a carbonyl group;
• comprising brominating an enamine of formula II ##STR7## wherein R.sub.1, R.sub.2, R.sub.3, X, Y and V have the meanings given above;
• and
• Z is a carbon-to-carbon bond, a methylene group, or an oxygen atom;
• with elemental bromine in a lower alcohol of maximally 4 carbon atoms, wherein prior to brominating the enamine, adding 1-2 moles of methanesulfonic acid per mole of the enamine and 0.01-1 moles of an ortho ester per mole of the enamine, wherein the ortho ester is of formula III
• R.sub.4 C(OR.sub.5).sub.3 (III)
• wherein
• R.sub.4 is a hydrogen atom or an alkyl residue of 1 to 4 carbon atoms, and
• R.sub.5 is an alkyl group of 1 to 4 carbon atoms.