The general procedure for the synthesis of 2-chloro-5,6,7,8-tetrahydro-1,6-naphthyridine hydrochloride from 6-benzyl-2-chloro-5,6,7,8-tetrahydro-1,6-naphthyridine was as follows: 6-benzyl-2-chloro-7,8-dihydro-5H-1,6-diazanaphthalene (2.70 g, 10.43 mmol, 1.00 eq.) was dissolved in ethylene chloride (50.00 mL) in dichloroethane (50.00 mL) and 1-chloroethyl carbonyl chloride (2.24 g, 15.65 mmol, 1.50 eq.) was added. The reaction was carried out at 15 °C under nitrogen protection. The reaction mixture was warmed up to 85 °C and the reaction was stirred for 12 hours. After completion of the reaction, the solvent was removed by concentration under reduced pressure. Methanol (50.00 mL) was added to the residue, heated to 80 °C and stirred for 2 hours. The reaction mixture was cooled and filtered, the filter cake was collected and dried to afford 2-chloro-5,6,7,8-tetrahydro-1,6-diazanaphthalene hydrochloride (2.00 g, 9.75 mmol, 93.50% yield) as a white solid. The resulting product was used directly in the next reaction without further purification.
