13301-04-7

Step 2: Methyl 3-amino-6-bromopyrazine-2-carboxylate (28.5 g, 120 mmol) was suspended in a mixed aqueous solution of 48% hydrobromic acid (120 mL) and acetic acid (30 mL) and cooled to 0 °C. The solution was then slowly added dropwise over a period of 45 minutes. Subsequently, a solution of bromine (18 mL, 336 mmol) in acetic acid (18 mL) was added slowly and dropwise over 45 minutes. While maintaining the reaction temperature at 0 °C, a solution of sodium nitrite (8.28 g, 420 mmol) in water (15 mL) was added and stirring was continued for 30 min. The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, excess bromine was quenched by dropwise addition of 30% aqueous sodium bisulfite solution (180 mL). The resulting precipitate was collected by filtration and purified by silica gel column chromatography using a hexane solution of 10% ethyl acetate as eluent to afford methyl 3,6-dibromopyrazine-2-carboxylate as a white crystalline solid (18 g, 49% yield). Mass spectrum (electrospray ionization) m/z: 294 ([M+H]+).

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