Prepare a fresh solution of acetic anhydride (4.8 ml.) and 70% aqueous perchloric acid (0.01 ml.) in ethyl acetate (50 ml.) then add dl-13-methyl-17α-ethynyl-3-methoxygona-2,5(10)-dien- 17-Ol (0.5 g.) as a solid, swirl for 1.5 minutes then quench the reaction by adding saturated aqueous sodium bicarbonate solution. Wash the ethyl acetate layer with saturated bicarbonate, brine and dry over anhydrous sodium sulfate. Filter, evaporate in vacuo then add methanol with a trace of pyridine and let stand for 2 hours. Evaporate in vacuo, pump dry then treat the residue in ether with decolorizing charcoal. Filter, evaporate and crystallize the residue from methanol to obtain dl-13-methyl-17α-ethynyl-17-hydroxygon-4-en-3-one, acetate.
