In 40 ml of acetone is dissolved 0.6 g of cyclopentanecarboxylic acid, and 6.0 ml of 1N-NaOH and 16 ml of water are added, followed by addition of 1.2 g of 16β-ethyl-17β-bromoacetoxy-4-estren-3-one. The mixture is refluxed for 6 hours. The solvent is distilled off under reduced pressure and the residue is extracted with 150 ml of ethyl acetate. The organic layer is separated, washed with water and saturated aqueous sodium chloride solution and dried over anhydrous magnesium sulfate. The solvent is then distilled off under reduced pressure and the residue is subjected to column chromatography. After serial passage of diisopropyl ether-n-hexane mixtures (1:9, 200 ml; 2:8, 200 ml; and 3:7, 200 ml), elution is carried out with 800 ml of a 1:1 mixture of the same solvents. The eluate is evaporated under reduced pressure to remove the solvent, giving 1.38 g of the above-identified compound as a colorless viscous oil.
