[F:1][C:2]([F:28])=[C:3]1[CH2:8][CH2:7][C@H:6]2[C@H:9]3[C@H:18]([CH2:19][CH2:20][C@:4]12[CH3:5])[C:17]1[CH:16]=[CH:15][C:14]([O:21]C2CCCCO2)=[CH:13][C:12]=1[CH:11]=[CH:10]3.C(O)(=O)C(O)=O>CO.O>[F:1][C:2]([F:28])=[C:3]1[CH2:8][CH2:7][C@H:6]2[C@H:9]3[C@H:18]([CH2:19][CH2:20][C@:4]12[CH3:5])[C:17]1[CH:16]=[CH:15][C:14]([OH:21])=[CH:13][C:12]=1[CH:11]=[CH:10]3A suspension of 1.1 g of 17-difluoromethylene-3-tetrahydropyranyloxy-estra-1,3,5(10),6-tetraene in 25 ml of methanol and 2.5 ml of water is refluxed at a bath temperature of 100° C. with 1.1 mg of oxalic acid for 1.5 hours. Then, it is added to water, extracted with dichloromethane, washed with water, sodium bicarbonate solution as well as with saturated sodium chloride solution, dried on sodium sulfate, concentrated by evaporation in a vacuum and chromatographed on silica gel with hexane/ethyl acetate. 0.6 g of 17-difluoromethylene-estra -1,3,5(10),6-tetraen-3-ol is obtained as colorless crystals with a melting point of 132-134° C., [α]D22 =-167.9° (c=0.505% in. pyridine).
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