Step 3: Synthesis of 2-bromo-5-methylmercaptopyrazine
To a stirred solution of 2,5-dibromopyrazine (0.45 g, 1.892 mmol) in anhydrous THF (5 mL) was slowly added 21% aqueous sodium methanethiol (0.94 mL, 2.83 mmol) dropwise under nitrogen protection. The reaction system was stirred at 0 °C for 1 h and the progress of the reaction was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was diluted by adding dichloromethane (DCM) and washed with deionized water. The organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give 2-bromo-5-methylmercaptopyrazine (0.3 g, 78% yield) as a brown oil. Mass spectrum (MS): 206.08 [M+H]+.
