General procedure for the synthesis of 5-bromo-6-trifluoromethylpyrimidin-4-one from 6-trifluoromethyl-4-hydroxypyrimidine: To a solution of acetic acid (2 mL) containing 8-(bromomethyl)pyrido[2,3-d]pyridazin-5(6H)-one (0.3 g, 1.8 mmol) was added CH3COOK (0.54 g, 5.5 mmol). Subsequently, a solution of bromine (Br2) in acetic acid (1 mL) was added dropwise to the reaction mixture. The reaction mixture was heated to 80 °C and stirred overnight. Upon completion of the reaction, the mixture was cooled to room temperature, diluted with ethyl acetate (EtOAc), washed sequentially with water and brine, dried over anhydrous sodium sulfate (Na2SO4), and finally the target product, 5-bromo-6-(trifluoromethyl)-4(3H)-pyrimidinedione (0.3 g), was obtained by evaporation of the solvent.
