The general procedure for the synthesis of (R)-N6-propyl-4,5,6,7-tetrahydrobenzothiazole-2,6-diamine dihydrochloride using (R)-N-(2-amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-propanamide as starting material was as follows: under nitrogen protection, (R)-N-(2-amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-propanamide (10 g, 33.43 mmol) with dichloromethane (100 mL) was added to a round bottom flask, stirred for 10-15 min and then cooled to 0-5 °C. Subsequently, trimethylsilyl chloride (5.1 mL, 40.12 mmol) was slowly added over 10-15 minutes and stirring was continued at the same temperature for 10-15 minutes. A tetrahydrofuran solution of lithium aluminum hydride (19.5 mL, 46.81 mmol) was added dropwise at -10°C to 0°C. After dropwise addition, the reaction mixture was kept at 0-10 °C and stirring was continued for 1-2 hours. Upon completion of the reaction (monitored by thin layer chromatography), 2M sodium hydroxide solution (30 mL) was slowly added dropwise to quench the reaction and stirred for 10-15 minutes. After separating the aqueous and organic layers, the target compound was extracted from the aqueous layer with dichloromethane (50.0 mL). The organic layers were combined and washed with 20% NaCl solution. Finally, the dichloromethane layer was concentrated to give a crude product which was dissolved in isopropanol (50.0 mL).
