General procedure for the synthesis of 5-bromo-3-chloropyrazin-2-amine from 2-amino-3-chloropyrazine: a suspension of N-bromosuccinimide (NBS, 31.0 g, 173 mmol) and 2-amino-3-chloropyrazine (20.0 g, 154 mmol) in chloroform (140 mL) was heated and refluxed for 16 hours. Upon completion of the reaction, the solution was cooled to room temperature and washed with deionized water (350 mL). The organic layer was filtered through diatomaceous earth and subsequently concentrated under reduced pressure to give 5-bromo-3-chloropyrazin-2-amine (22.0 g, 69% yield) as a brown solid. The melting point of the product was 230-232 °C; the IR spectrum (thin film method, cm^-1 ) showed 3412 (NH2 stretching vibration), 3019 (aromatic C-H stretching vibration); the NMR hydrogen spectrum (500 MHz, CDCl3) δ 5.02 (2H, broad single peak, NH2), 8.05 (1H, single peak, 6-H); the NMR carbon spectrum (125 MHz , CDCl3) δ 123.5, 132.0, 142.9, 150.6; gas chromatography-mass spectrometry (GC-MS) showed m/z 211, 209, 207 (M+); gas chromatography retention time (tR) was 2.82 min; purity was >99%; high-resolution mass spectrometry (HRMS) measured value: m/z 207.9280 for MH+; calculated value: 207.9272.
