Patent ID: 8153648

Claim:
A process to prepare crystalline Dutasteride Form III, comprising the following steps: a. reacting 4-aza-5α-androst-1-ene-3-one-17β-carboxylic acid with at least one acyl halide selected from the group consisting of methansulfonyl chloride, p-toluensulfonyl chloride and pivaloyl chloride in an aprotic solvent and in the presence of a scavenger of HCl at a temperature below 10° C.; b. reacting the intermediate substances generated in the step a. with 2,5-bis(trifluoromethyl)aniline in the presence of a Lewis acid; c. heating to reflux until reaction complete; d. distilling the solvent to obtain a solid residue or a concentrated solution; e. adding water to the concentrated solution obtained in d. to produce a suspension; f. filtering the suspension to obtain a solid; g. dissolving the solid in organic solvent after that water is added to obtain a suspension; h. filtering the suspension and drying the solid; i. dissolving the solid residue obtained in d. in an organic solvent, then washing the organic phase with an aqueous solution to eliminate inorganic impurities; j. distilling the solvent of organic phase i. to obtain a suspension; and k. filtering the suspension obtained in j. and drying the solid.