Microwave induced selective enolization of steroidal ketones and efficient acetylation of sterols in semisolid state

Under microwave irradiation steroidal enones, more specifically, position three carbonyls were efficiently and selectively converted to the corresponding enol acetates in the presence of additional enolizable carbonyl functions at other positions, using acetic anhydride and a catalytic amount of toluene-p-sulfonic acid. Acetylation of hydroxyl groups of the sterols, including those at the hindered positions, was near quantitative. Strictly anhydrous conditions were not a pre-requisite for acetylation and the reaction system easily tolerated up to 10% (v/v) moisture.