A solution of 9.4 g of diethyl-(difluoromethyl)-phosphonate in 150 ml of tetrahydrofuran is slowly mixed with 25 ml of 2 M lithium diisopropylamide solution at a bath temperature of -50° C., and it is stirred for 1 hour. Then, a solution of 6 g of 3-methoxy-18-methyl-estra-1,3,5(10)-trien-17-one in 173 ml of tetrahydrofuran is slowly added, stirred for 15 minutes, slowly heated at a bath temperature of from -50° C. to 100° C. and refluxed for 6 hours. For working-up, it is diluted with ethyl acetate, washed with water 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. 5.4 g of 17-difluoromethylene-3-methoxy-18-methyl-estra -1,3,5(10)-triene is obtained as colorless crystals with a melting point of 145-146° C., [α]D22 =+40.2° (c=0.515% in pyridine).
