A solution of 715 mg of difluoromethyldiphenylphosphine oxide in 36 ml of tetrahydrofuran is slowly mixed with 1.42 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 1 g of 3-tetrahydropyranyloxy-estra-1,3,5(10),6-tetraen-17-one in 10 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 2.5 hours. For working-up, it is added to water, extracted with ethyl acetate, washed with water as well as with saturated sodium chloride solution, dried on sodium sulfate and concentrated by evaporation in a vacuum. 1.1 g of 17-difluoromethylene-3-tetrahydropyranyloxy-estra-1,3,5(10),6-tetraene is obtained as colorless crystals.
