General procedure for the synthesis of 2,4-dibromo-5-methylpyrimidine from 5-methyluracil: Thymine (3.7 g, 29 mmol) and phosphorus pentoxide (25.0 g, 87.2 mmol) were dissolved in acetonitrile (150 mL) at 0 °C, followed by batchwise addition of potassium carbonate (12.1 g, 87.2 mmol). The reaction mixture was gradually warmed to room temperature, then heated to 80 °C and maintained for 3 days. Upon completion of the reaction, the mixture was poured into ice water and the pH was adjusted with solid potassium carbonate to 7. The aqueous layer was extracted with dichloromethane and the organic layer was sequentially washed with brine, dried over anhydrous magnesium sulfate, filtered and concentrated. Purification by silica gel column chromatography (eluent: 0-30% ethyl acetate/hexane) afforded the target product 2,4-dibromo-5-methylpyrimidine (7.1 g, 96% yield) as a white solid. lC-MS (ES) m/z = 251, 253 and 255 [M + H]+ .
