(b) Synthesis of 4,6-dichloropyridine-2,3-diamine (A92): iron powder (0.68 g, 12 mmol) and NH4Cl (0.64 g, 12.2 mmol) were sequentially added to stirring 4,6-dichloro-3-nitropyridin-2-amine A91 (0.51 g, 2.5 mmol) in a suspension of water (11 mL) and propan-2-ol ( 22 mL) mixture in suspension. The reaction mixture was then heated to 70 °C and kept for 2 hours. Upon completion of the reaction, the mixture was filtered through diatomaceous earth and washed with EtOAc (150 mL). The combined organic phases were washed sequentially with saturated aqueous NaHCO3 and brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give the title compound as light brown crystals (0.39 g, 89% yield).1H NMR (400 MHz, CDCl3) δ 5.76 (s, 1H), 4.44 (s, 2H), 3.56 (s, 2H).LCMS-A : retention time 5.53 min, m/z (positive ion mode) 178.1 [M + H]+.
