704911-47-7

3641-14-3

704911-47-7

Step 1: Synthesis of methyl 5-bromo-1H-1,2,4-triazole-3-carboxylate (306a) Methyl 5-bromo-1H-1,2,4-triazole-3-carboxylate (6.5 g, 45 mmol) was suspended in a mixed solution of sulfuric acid (6 mL) and water (100 mL). An aqueous solution of sodium nitrite (6.4 g, 67 mmol) was slowly added to the suspension at -3 °C. After 30 min of reaction, an aqueous solution of freshly prepared copper bromide (4.2 g, 21 mmol) and potassium bromide (13.0 g, 91 mmol) was added dropwise at the same temperature. The reaction mixture was stirred at 25 °C for 3 hours. After completion of the reaction, the mixture was extracted with ethyl acetate. The crude product was purified by column chromatography (dichloromethane/methanol=20/1) to give compound 306a (5.5 g, 58% yield) as a white solid.