3.7 g. of diphenyldiselenide is dissolved in 200 ml. of absolute ethanol and combined at room temperature with 1.0 g. of sodium borohydride. After the yellow solution has lost its color, 5.0 g. of 16α,17α-epoxy-3-methoxy-18 -methyl-1,3,5(10)-estratriene is added thereto and the mixture is heated under reflux for 30 hours. The solution is then cooled to 0° C. Dropwise, 11ml. of 30% H2O2 is added to the reaction solution and the latter is then gradually heated to 50° C. After 2 hours, the solution is introduced into ice water. The precipitate is vacuum-filtered, washed with water, and taken up in methylene chloride. After chromatography on silica gel with 6-8% acetone/hexane, 1.9 g. of 3-methoxy-18-methyl-1,3,5(10),15-estratetraen-17α-ol is obtained as an oily product. [α]D 20 = -108°.
