Patent ID: 7638542

Claim:
A process for preparing 2-amino-6-alkyl-amino-4,5,6,7-tetrahydrobenzothiazoles of formula (I) wherein the asterisk (*) indicates the presence of an asymmetric carbon and R 1 is a linear or branched C 1 -C 6 alkyl group; their enantiomers or mixtures thereof, hydrates of pramipexole or pharmaceutically acceptable salts, comprising the following steps: (a) reacting a compound of formula (II) wherein the asterisk (*) and R 1 have the previously mentioned meanings, with a secondary amine of formula NHR 2 R 3 wherein R 2 and R 3 are, independently of one another, C 1 -C 3 alkyl groups, or R 2 and R 3 together form a divalent C 4 -C 5 radical, or a —CH 2 CH 2 OCH 2 CH 2 — radical, forming a cycle with the nitrogen atom to which it is attached; optionally in the presence of an acid and a solvent 1, to form an enamine of formula (III) wherein the asterisk (*), R 1 , R 2 and R 3 have the previously mentioned meanings; (b) optionally removing said acid and said solvent 1, and then reacting the compound of formula (III) with sulfur in the presence of a solvent 2 to obtain the compound of formula (IV) wherein the asterisk (*) and R 1 have the previously mentioned meanings, and finally (c) reacting the compound of formula (IV) with cyanamide to obtain the compound of formula (I).