General procedure for the synthesis of 4-bromo-2-(methylthio)pyrimidine from 2-methylthio-4-bromopyrimidine: ammonium molybdate tetrahydrate (1.09 g, 0.88 mmol, 0.03 eq.) was added in batches to a stirred solution of 30% H2O2 (6 g, 29.4 mmol, 1 eq.) at 0 °C for 20 min. Subsequently, a solution of 4-bromo-2-(methylthio)pyrimidine (6 g, 29.41 mmol, 1 eq.) was slowly added, keeping the reaction temperature at 0 °C. After addition, the reaction mixture was brought to room temperature and stirred for 3 hours. The reaction progress was monitored by TLC. Upon completion of the reaction, the reaction mixture was concentrated to a crude residue, diluted with cold water and then extracted with dichloromethane (DCM, 3 x 100 mL). The organic layers were combined, washed sequentially with 5% H2SO4 solution and water, dried over anhydrous Na2SO4 and concentrated to give the crude product. The crude product was purified by silica gel column chromatography (100-200 mesh) with the eluent being a petroleum ether solution of 0-40% ethyl acetate, resulting in 4-bromo-2-(methylsulfonyl)pyrimidine (6 g, 86% yield) as an off-white solid.LCMS: [M + H]+ 238.84.
