[N+]([O-])(O)=O.[CH3:5][C:6]1[NH:11][C:10](=[O:12])[NH:9][CH:8]([C:13]2[CH:18]=[CH:17][C:16]([CH3:19])=[CH:15][CH:14]=2)[C:7]=1[C:20]([O:22][CH2:23][CH3:24])=[O:21].C(=O)([O-])[O-].[K+].[K+]>O>[CH3:5][C:6]1[NH:11][C:10](=[O:12])[N:9]=[C:8]([C:13]2[CH:18]=[CH:17][C:16]([CH3:19])=[CH:15][CH:14]=2)[C:7]=1[C:20]([O:22][CH2:23][CH3:24])=[O:21]To a cold (0° C.) mixture of nitric acid (70%) (34 ml) and water (6 mL) was added ethyl 6-methyl-2-oxo-4-p-tolyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate (6 g; 21,87 mmol) in small portions (within 3 min). The mixture was stirred for 30 min while gradually allowed to reach room temperature. The reaction was poured onto crushed ice and neutralized by adding potassium carbonate until pH 8. The aqueous layer was extracted with chloroform (3 times) and the combined organics were dried over sodium sulphate, filtered and concentrated under reduced pressure. The obtained green oil was dissolved in dichloromethane and concentrated under reduced pressure to afford a green solid, which was crystallized from ethanol and the obtained greenish crystals were triturated with heptane to furnish 3.7 g (60%) of the title compound as a white-to-green solid.
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