P(Cl)(Cl)([Cl:3])=O.[NH:6]1[C:13](=[O:14])[CH2:12][C:10](=O)[NH:9][C:7]1=[O:8]>O>[Cl:3][N:6]1[C:13](=[O:14])[CH:12]=[CH:10][NH:9][C:7]1=[O:8]Phosphoryl chloride (55 ml) is carefully added to barbituric acid (10 g, 78.1 mmol) at 0° C. Water (1.7 ml) is then added dropwise such that the temperature does not exceed 5° C. The mixture is boiled under reflux for 5 h and, after it has cooled down, poured onto ice. The product is extracted with ethyl acetate (3×100 ml) and dried (Na2 SO4). The mixture is filtered and the solvent is distilled off in vacuo.
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