Bile acids. LXVIII. Allylic and benzylic photo-chemical oxidation of steroids

To provide 7-oxocholesterol derivatives in yields superior to those obtained by chemical oxidation, the preparation of steroidal allylic or benzylic ketones was studied. Air-induced oxidation was investigated with a highly selective low energy UV lamp in the presence of mercuric bromide. With this procedure cholesteryl acetate, 5-cholestene-3β, 27-diol diacetate, 24(R)-24-methyl-5-cholesten-3β-yl acetate, 24(R)-24-ethyl -5-cholesten-3β-yl acetate and 24(R)-24-ethyl-(22E)-cholesta-5, 22-dien -3β-yl acetate were oxidized to the allylic keto-derivative in good yields; estradiol-17β diacetate was similarly converted to the 6-oxo-product in improved yield. This method can be very useful in the synthesis of 7-oxocholesteryl acetate and its analogs and 6-oxoestratrienes.