A mixed solution of 1α,3β-bis(tert-butyldimethylsilyloxy)-20(R)-hydroxypregna-5,7,16-triene (51 mg, 0.0911 mmol), sodium hydride (50 mg, 2.08 mmol) and 4-bromo-2,3-epoxy-2-methylbutane (75 mg, 0.455 mmol) in tetrahydrofuran (2 ml) was heated under reflux for 1.5 hours and combined with 1M lithium tri-s-butylborohydride solution in tetrahydrofuran (0.9 ml, 0.900 mmol), and the mixed solution was heated under reflux for 20 minutes. The reaction solution was stirred with 3N aqueous sodium hydroxide solution and 30% aqueous hydrogen peroxide at room temperature for 30 minutes, then diluted with ethyl acetate, washed with brine and dried over magnesium sulfate. The solvent was distilled off under reduced pressure and the resulting residue was purified by preparative thin layer chromatography (0.5 mm×1, hexane:ethyl acetate=10:1, developed twice) to give the title compound as a colorless oil (48.6 mg, 83%).
