Step 2: Synthesis of 2-(methylthio)pyrimidine-5-boronic acid
Under nitrogen protection, 5-bromo-2-(methylthio)pyrimidine (0.05 g, 0.241 mmol) was dissolved in tetrahydrofuran (THF, 10 mL), stirred and cooled to -78 °C. Slowly n-butyllithium (0.15 mL, 0.36 mmol, 2.5 M hexane solution) was added, maintaining the temperature at -78 °C, and stirring was continued for 1 hour. Subsequently, triisopropyl borate (0.068 g, 0.361 mmol) was added dropwise and the reaction was stirred at the same temperature for 4 hours. The progress of the reaction was monitored by thin layer chromatography (TLC). After completion of the reaction, the reaction was quenched with ice water and then separated by extraction with saturated ammonium chloride (NH4Cl) solution and ethyl acetate (EtOAc). The organic layer was washed with brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product 2-(methylthio)pyrimidine-5-boronic acid (0.03 g, 73% yield) as an off-white solid. Mass spectrometry (MS) data: 171.1 [M+H]+.
