Patent ID: 7538230

Claim:
A method for preparing letrozole, the method comprising the steps of: reacting an activated bis-(4-cyanophenyl)-methane of the formula: wherein X is a halogen or a sulfonate ester, with 1,2,4-triazole or a salt thereof in the presence of one or more water-immiscible organic solvents to produce a reaction mixture containing letrozole, and, as an impurity, isoletrozole; optionally adding an organic acid to the reaction mixture; adding water and at least one water-miscible solvent to the reaction mixture to produce a system comprising at least two liquid phases and at least one solid phase, wherein the solid phase comprises letrozole; heating the system and allowing the mixture to cool, to selectively precipitate letrozole; isolating the letrozole; and optionally subjecting the isolated letrozole to one or more crystallizations, wherein the isolated and optionally crystallized letrozole has a purity of at least about 95% by HPLC and contains less than about 1 wt % isoletrozole.