A solution of 12.0 g of 21-acetoxy-6α-chloro-16α-methyl-1,4,9(11)-pregnatriene-3,20-dione in 120 ml of dioxane is stirred at room temperature after adding 11.1 g of N-bromosuccinimide and 60 ml of 10% perchloric acid and, after 60 minutes, poured into ice water. The thus-precipitated product is filtered off, washed with water, dried in the air, and dissovled in 215 ml of ethanol. After adding 29 g of potassium acetate, the solution is heated for 8 hours to 60° C. under argon. Then the mixture is concentrated to a volume of 60 ml under vacuum, and stirred into ice water. The precipitated product is isolated and chromatographed on silica gel. With 8-9% acetone-hexane, after recrystallization from acetone-diisopropyl ether, 5.2 g of 21-acetoxy-6α-chloro-9,11β-epoxy-16α-methyl-9β-pregna-1,4-diene-3,20-dione is obtained, m.p. 189° C. [α]D25 =+57° (chloroform).
