The general procedure for the synthesis of 4,6-dichloro-2-methylthiopyrimidine-5-carbaldehyde from 4,6-dihydroxy-2-methylthiopyrimidine was as follows: the reaction system was cooled down to 0-10 °C and then slowly warmed up to room temperature. Subsequently, 6-hydroxy-2-(methylthio)-4(1H)-pyrimidinone (25 g, 0.16 mol) was added in batches. The reaction mixture was heated and reacted at 80 °C overnight. After completion of the reaction, the reaction mixture was concentrated under vacuum. The concentrated slurry residue was poured into ice and stirred continuously for about 2 hours, after which filtration was performed to obtain the crude product. The crude product was further purified by recrystallization with hexane to afford finally 4,6-dichloro-2-(methylthio)-5-pyrimidinecarboxaldehyde (21.3 g, 61% yield). The structure of the product was confirmed by 1H-NMR (CDCl3): δ 2.66 (s, 3H), 10.4 (s, 1H).
