420 mg of (22E)-stigmasta-4,22-dien-3-one are dissolved in 100 mL of tert-butanol and the same volume of water is added. To this mixture 0.93 g of the chiral auxiliary DHQD2-Phal, 450 mg (2 mmol) methanesulphonamide, 4.5 g of potassium ferricianide, 2 g of potassium carbonate and 30 mg de potassium osmate are added. The mixture is vigorously stirred, at ambient temperature, during 9 days. The reaction, controlled by thin layer chromatography is not completed. Little portions of solid sodium bisulphate are added, until bubbling stops. The mixture is extracted with ethyl acetate, washed with 0.25M aqueous sulphuric acid, then with 10% NaOH 10%, and finally with water. The organic phase is dried and evaporated. The crude product is purified by column chromatography (eluting solvent: hexane/ethyl acetate 1:1). 180 mg of (22S,23S)-22,23-dihydroxystigmast-4-en-3-one are obtained, subsequently 165 mg of (22R,23R)-22,23-dihydroxystigmast-4-en-3-one are eluted.
