General procedure for the synthesis of 2-amino-5-bromo-6-chloropyrazine from 2-amino-6-chloropyrazine: 6-chloropyrazin-2-amine (10.4 g, 80 mmol) was dissolved in methanol (300 mL), and N-bromosuccinimide (15.6 g, 88 mmol) was added slowly with stirring at room temperature. The reaction mixture was continued to stir for 60 min and then concentrated under reduced pressure to remove the solvent. Water was added to the concentrate and extracted with ethyl acetate (3 x 100 mL). The organic phases were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography with the eluent being a solvent mixture of hashane and ethyl acetate (3:1, v/v) to afford the target compound 2-amino-5-bromo-6-chloropyrazine (12.0 g, 72% yield).1H NMR (500 MHz, CDCl3) δ 7.69 (s, 1H), 4.73 (s, 2H).
