5.6 g of crude 7α-(5-acetoxypentyl)-estra-1,3,5(10)-triene-3,17β-diol is dissolved in 35 ml of anhydrous tetrahydrofuran and mixed with 3.5 ml of dihydropyran and 0.18 g of p-toluenesulfonic acid. The mixture is stirred at room temperature overnight, then diluted with ethyl acetate, and the mixture is shaken out in succession with saturated sodium bicarbonate solution and saturated common salt solution. The organic phase is dried with sodium sulfate and concentrated by evaporation in a vacuum, yield 8.31 g.
