Benzoic Acid → 3alpha-Benzoyloxy-5alpha-pregnan-20-one

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A mixture of 3β-hydroxy-5α-pregnan-20-one (285 mg, 318.5 g/m, 0.89 mmol), triphenylphosphine (258 mg, 262.3 g/m, 0.94 mmol), and benzoic acid (120 mg, 122.2 g/m, 0.98 mmol) was dissolved in 25 mL of tetrahydrofuran (freshly distilled). To this stirred reaction mixture at room temperature was added a solution of diisopropylazidodicarboxylate (DIAD) (0.194 mL, 1.027 g/ml, 202.2 g/m, 0.98 mmol) in 5 mL of tetrahydrofuran dropwise over a period of 5 minutes. The reaction was followed by thin layer chromatography (TLC) as the starting material was consumed. After two hours, the reaction mixture was concentrated under reduced pressure and filtered through a bed of silica gel (10 g) with a mixture of hexane/ethyl acetate (9:1). Fractions corresponding to the title compound were concentrated to give 349 mg of 3α-benzoyloxy-5α-pregnan-20-one (92% yield) as a white solid.

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