General procedure for the synthesis of 3,5-dichloropyrazin-2-amine from 2-amino-3-chloropyrazine: 2-amino-3-chloropyrazine (10.0 g, 77.2 mmol) was added to a stirred suspension of N-chlorosuccinimide (NCS, 11.6 g, 86.9 mmol) in chloroform (73 mL). The reaction mixture was heated to reflux for 4 hours. Upon completion of the reaction, the solution was cooled to room temperature and partitioned between chloroform (180 mL) and water (2 x 50 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography using chloroform as eluent to afford 3,5-dichloropyrazin-2-amine (9.66 g, 76% yield) as a light yellow solid. The product characterization data were as follows: melting point 200-202°C; thin layer chromatography Rf value (CHCl3) 0.32; infrared spectra (thin film method, cm^-1) 3411 (NH2 telescoping vibration), 3019 (aromatic CH telescoping vibration); elemental analyses (measured values: C, 28.89; H, 1.71; N, 24.99; C4H3N3Cl2-0.125); H2O theoretical values: C, 28.89; H, 1.71; N, 24.99; C4H3N3Cl2-0.125). H2O theoretical values: C, 28.90; H, 1.97; N, 25.28%); 1H NMR (500 MHz, CDCl3) δ 4.96 (2H, broad single peak, NH2), 7.90 (1H, single peak, 6-H); 13C NMR (125 MHz, CDCl3) δ 131.4, 134.6, 140.0, 150.3; Gas chromatography-mass spectrometry (GC-MS) m/z 167, 165, 163 (M+), retention time 2.51 min; purity 98%; high-resolution mass spectrometry (HRMS) measured value: MH+ m/z 163.9782, calculated value 163.9777.
