2-((10S,13S)-10,13-dimethyl-3-oxo-6,7,8,10,12,13,14,15-octahydro-3H-cyclopenta[a]phenanthren-17-yl)-2-oxoethyl acetate (1 kg, 2.73 mol), acetone (50 L) and purified water (2.6 L) were added to the reaction vessel, and dissolved by stirring at room temperature; Formic acid (0.4 L, 10.60 mol) and potassium permanganate (1.2 kg, 7.59 mol) were added in that order, and the reaction was stirred at room temperature for 1 h. The reaction was quenched by the addition of saturated sodium hydrogen sulfite solution (10 L) and manganese dioxide, and some solid impurities were removed by suction filtration, and the filtrate was evaporated under reduced pressure to give a large white solid. The filter cake was washed with water to give 16alpha,17,21-trihydroxypregna-1,4,9(11)-triene-3,20-dione 21-acetate (1.01 kg, 92.2%).
