General procedure for the synthesis of 5,6-dichloropyridine-2,3-diamine from 2-amino-3-nitro-5-chloropyridine: 5-chloro-3-nitropyridin-2-amine (2000.0 mg, 11.52 mmol) and stannous chloride (8740.0 mg, 46.09 mmol) were added slowly in a reaction vial. Hydrochloric acid (20.0 mL) was then added and the reaction mixture was stirred at 80-100 °C for 0.5 hours. Upon completion of the reaction, the pH was neutralized by adjusting to 7 with saturated 1N aqueous sodium hydroxide solution and then extracted with ethyl acetate (200.0 mL). The organic layer was washed with saturated saline, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (hexane: ethyl acetate = 90:10). The fraction containing the target product was collected and the solvent was evaporated under reduced pressure to give 5,6-dichloropyridine-2,3-diamine as an ivory-colored solid (1000.0 mg, 49% yield).1H-NMR (300 MHz, DMSO-d6) δ: 6.80 (s, 1H), 6.04 (s, 2H), 5.11 (s, 2H).
