Oxidation of Ring-A Aromatic Steroids

by Carlisle, Valerie F.

This thesis is concerned with a study of the oxidation of ring-A aromatic steroids using either chromium trioxide-aqueous sulphuric acid-acetone or chromium trioxide-aqueous acetic acid mixtures. It was found that chromic acid oxidation of ring-A aromatic steroids substituted with a strong electron-donating group, gives rise to products with the site of oxidation being predominantly that para to the activating group. Thus C-3 methoxy ring-A aromatic steroids give the corresponding 9b-hydroxy-11-oxo and 9-oxo-9,11-seco-11-oic acid derivatives as the major products and the 6-oxo derivative as a minor oxidation product. However, a ketol was not formed if a C-3 methoxy ring-A aromatic steroid also contained a substituent at C-1. The C-1-methoxy-4-methyl ring-A aromatic steroids give the 4-carboxy derivative as the major product and again the 6-oxo compound as a minor neutral product. The acetoxy and methyl substituted ring-A aromatic steroids, however, all give rise to the 6-oxo derivatives as the major products. The usual oxidation product of a ring-A aromatic steroid is therefore the 6-oxo product unless it is substituted with a methoxy group in a position which will stabilise an electron deficiency at a site other than C-6. Oxidation will then occur predominantly at the stabilised site unless it is sterically blocked.