[NH2:1][C:2]1[N:7]([CH2:8][C:9]2[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=2)[C:6](=[O:15])[NH:5][C:4](=[O:16])[CH:3]=1.[N:17]([O-])=[O:18].[Na+].Cl>CN(C)C=O.O>[NH2:1][C:2]1[N:7]([CH2:8][C:9]2[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=2)[C:6](=[O:15])[NH:5][C:4](=[O:16])[C:3]=1[N:17]=[O:18]To a solution of 6-amino-1-benzyl-1,3-dihydropyrimidine-2,4-dione (2.0 g, 9.2 mmol) in a mixture of 15 ml of N,N-dimethylformamide and 5 ml of water at 90° C. was added sodium nitrite (1.27 g, 69 mmol). To this reaction mixture was added concentrated hydrochloric acid until there was no deepening of color, and the mixture was heated at 70° C. for 1 hour. The solvent was removed under reduced pressure, the residue dissolved in water, and concentrated hydrochloric acid added to produce a pH of 4.0. The precipitate was filtered off, washed with water, and dried under reduced pressure, to provide 6-amino-5-nitroso-1-benzyl-1,3-dihydropyrimidine-2,4-dione, a compound of formula (23).
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