A solution of 1.2 g (2.97 mmole) of 11β-acetyloxy-17-(ethylthio)-9-fluoroandrosta-1,4,16-trien-3-one, 18 ml of dry dichloromethane and 0.8 ml of thiophenol is cooled to -20° C. under nitrogen. Boron trifluoride etherate (0.6 ml) is then added. The solution is stirred at -10° to -20° C. for 2 hours under nitrogen. The resulting solution is diluted with dichloromethane, washed with saturated sodium bicarbonate and water, dried over anhydrous Na2SO4 and evaporated in vacuo to give a gum. This is dissolved in chloroform-hexane (1:1) and chromatographed on a 20 g-silica gel column, eluting successively with chloroform-hexane (1:1), chloroform, chloroform-ethyl acetate (95:5) and chloroform-methanol (9:1) to give 1.0 g of impure title compound. This is dissolved in the minimum amount of ethyl acetate and stood at room temperature for 2 days. The solid that precipitates is filtered to give 480 mg of title compound, melting point 152°-158° C., with consistent spectral data.
