In 30 ml of dichloromethane are dissolved 3.2 g of 16β-ethyl-17β-hydroxy-4-estren-3-one and 1.2 ml of dimethylaniline and, with stirring at room temperature (15°-25° C.), 1.0 ml of 2-bromo-2-methylpropionyl bromide is added to the above solution. The mixture is stirred at room temperature (15°-25° C.) for 16 hours, followed by addition of 300 ml of ethyl acetate. The mixture is washed with 10% phosphoric acid, water, 5% aqueous sodium hydrogen carbonate and saturated aqueous sodium chloride in that order and dried over anhydrous magnesium sulfate. The solvent is then distilled off under reduced pressure and the residue is subjected to column chromatography. Following passage of 400 ml of diisopropyl ether-n-hexane (1:1), elution is carried out with 800 ml of the same solvent system. The eluate is evaporated under reduced pressure to remove the solvent, giving 2.6 g of the above-identified compound as a light-yellow viscous oil.
