General procedure for the synthesis of 2-(trifluoromethyl)-5,6,7,8-tetrahydro-1,6-naphthyridine hydrochloride from 6-benzyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro-1,6-naphthyridine: 21.3 g (0.073 mol) of 6-benzyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro-1,6-naphthyridine was added to a 200 mL reaction flask containing 500 mL solvent in a 200 mL reaction flask containing 500 mL of solvent and stirred at room temperature. 13.6 g (0.095 mol) of 1-chloroethyl chloroformate solution was slowly added to the reaction solution and stirring was continued for 15 minutes after addition. The reaction mixture was then heated to reflux temperature and maintained for 20 hours and then cooled to room temperature. Upon completion of the reaction, 200 mL of solvent was removed by distillation under reduced pressure. Methanol was added and heated to reflux for 3 hours. At the end of the reaction, 200 mL of ethyl acetate was added and the solvent was removed by distillation under reduced pressure to give a white solid precipitate. After stirring for 30 minutes, the white solid was collected by filtration and dried to give a product of 10.8 g with a melting point of 241.1 °C.
