P(Cl)(Cl)([Cl:3])=O.[Cl:6][C:7]1[C:12]([Cl:13])=[C:11]([C:14]2[N:19]=[C:18](S)[N:17]([CH3:21])[C:16](=[O:22])[CH:15]=2)[CH:10]=[CH:9][N:8]=1>CN(C)C=O>[Cl:3][C:18]1[N:17]([CH3:21])[C:16](=[O:22])[CH:15]=[C:14]([C:11]2[CH:10]=[CH:9][N:8]=[C:7]([Cl:6])[C:12]=2[Cl:13])[N:19]=1After one hour stirring of a solution of phosphorus oxychloride (2.9 g, 18.9 mmol) in dimethylformamide (30 ml) at room temperature, 6-(2,3-dichloropyridin-4-yl)-2-mercapto-3-methyl-3H-pyrimidin-4-one (3.58 g, 12.4 mmol) was added and heated at 60° C. for 2 hours. The resulting suspension was partitioned between ethyl acetate and saturated aqueous sodium bicarbonate and the aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with brine, dried over magnesium sulfate, and concentrated in vacuo. The residue was washed by hexane to furnish 2-chloro-6-(2,3-dichloropyridin-4-yl)-3-methyl-3H-pyrimidin-4-one (2.6 g, 8.95 mmol, 72%) as white crystals.
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