Patent ID: 7365208

Claim:
A method for preparing a compound of formula II in substantially pure form comprising reacting a mixture of a compound of formula IVa and a compound of formula IVb, and optionally a compound of formula IVc, with a compound of formula V, or a pharmaceutically acceptable salt thereof, in the presence of a base and a reducing agent, and optionally in the presence of a phase transfer catalyst to form the compound of formula II, and carrying out the following steps to prepare the compound of formula II in substantially pure form: (a) crystallizing the compound of formula II with at least one solvent selected from methyl tert-butyl ether and iso-propanol to give a compound of formula II in crystal form; (b) washing the compound of formula II in crystal form from step (a) with at least one solvent selected from methyl tert-butyl ether and iso-propanol to give the compound of formula II in substantially pure form; and (c) recycling the washed solvent collected from step (b) to crystallize a crude compound of formula II in the next batch as recited in step (a).