Abstract: A process for the preparation of a compound of the formula ##STR1## wherein R.sub.1 is selected from the group consisting of hydrogen, alkyl of 1 to 4 carbon atoms optionally substituted by halogen or a nitrogen or oxygen function and alkenyl and alkynyl of 2 to 4 carbon atoms, R.sub.2 is alkyl of 1 to 4 carbon atoms and the A, B, C and D rings are optionally substituted by at least one member of the group consisting of optionally protected --OH or .dbd.0, halogen, alkyl and alkoxy of 1 to 4 carbon atoms and alkenyl and alkynyl of 2 to 4 carbon atoms comprising reacting a compound of the formula ##STR2## wherein R.sub.1 and R.sub.2 and the A, B, C and D rings are defined as above with an oxidizing agent in the presence of water and an at least partially water-miscible solvent to obtain a compound of the formula ##STR3## wherein R.sub.1 and R.sub.