A method for preparing 6alpha,9alpha-difluoro-17alpha-[(2-furanylcarbonyl)oxy]-11ss-hydroxy-16alpha-methyl-3-oxoandrosta-1,4-diene-17ss-carbothioicacid S-fluoromethyl ester from a thiocarboxylic acid by reacting the thiocarboxylic acid with a solution containing chlorofluoromethane and a mild base medium at a temperature in the range of -60° C to 90° C.
