Direct electrochemical acetoxylation of cholesterol at the allylic position

It has been found that cholesterol undergoes direct electrochemical oxidation on platinum electrode in glacial acetic acid containing sodium perchlorate and sodium acetate as supporting electrolytes. Voltammetric measurements show that the process is controlled by the rate of electron transfer and the height of the oxidation peak is linear vs. concentration of cholesterol. Preparative electrolysis afforded two major products: 7 alpha-acetoxycholesterol and 7 beta-acetoxycholesterol in the ratio 10:3, as established by integration of the C-6 proton signals in the H-1 NMR spectrum. The same products were obtained when sodium acetate was replaced by sodium trifluoro acetate but stereo selectivity was lost (product ratio 1:1) at that time. Easy thermal elimination of acetic acid from the products may be potentially used for the synthesis of 7-dehydrocholesterol (provitamin D-3). (c) 2005 Elsevier B.V. All rights reserved.