Preparation of compound 36a: 3,5-dibromopyrazin-2-ol
To a stirred solution of 3,5-dibromopyrazin-2-amine (30 g, 0.12 mol) in acetic acid (300 mL) was added sulfuric acid (50 mL) dropwise at 15-25 °C. Subsequently, a solution of sodium nitrite (16.6 g, 0.24 mol) in water (100 mL) was added dropwise to the resulting solution over a period of 1.5 hours at 10-15°C. After the dropwise addition was completed, the reaction mixture was continued to be stirred at 10-15 °C for 1 hour. The reaction mixture was poured into water (3L) and extracted with ethyl acetate (1L x 3). The organic layers were combined, washed sequentially with saturated sodium bicarbonate solution (1L×3) and brine (1L), dried with anhydrous sodium sulfate, and concentrated under reduced pressure to afford 3,5-dibromo-2-hydroxypyrazine (36a) as a yellow solid (24 g, 79.4% yield).
1H NMR (400 MHz, CDCl3): δ 7.44 (s, 1H).
