To a suspension of 4 mg (0.1 mmole) of lithium aluminum hydride in 4 ml of dry tetrahydrofuran was added a solution of 3.8 mg (0.00887 mmole) of 20-(5,5-dimethyl- 1,3-dioxan-2-yl)-1α,2α-epoxypregna-5,7-dien-3β-ol in 2 ml of dry tetrahydrofuran at a temperature of 60° C. and the mixture was stirred at 60° C. for 30 minutes. To the reaction mixture was added water to decompose the excess lithium aluminum hydride and the tetrahydrofuran was distilled off under reduced pressure at a temperature not exceeding 60° C. To the residue was added cold 1N-hydrochloric acid and the mixture was extracted with chloroform. The extract was washed with aqueous sodium chloride solution and dried over magnesium sulfate. The solvent was then distilled off under reduced pressure and the residue was purified by silica gel chromatography (eluent: ethyl acetate-hexane=1:5, v/v) to give 3 mg of 20-(5,5-dimethyl-1,3-dioxan-2-yl)pregna-5,7-diene-1α,3β-diol (yield: ca. 80%).
