[NH2:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[N:8]([CH3:12])[C:7](=[O:13])[C:6](=[O:14])[NH:5]2.[C:15](OC(=O)C)(=[O:17])[CH3:16]>O.[OH-].[Na+]>[C:15]([NH:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[N:8]([CH3:12])[C:7](=[O:13])[C:6](=[O:14])[NH:5]2)(=[O:17])[CH3:16]To a solution of 0.3 g (1.3 mmol) 6-amino-1-methylquinoxaline-2,3(1H,4H)-dione in a mixture of 15 ml water and 0.6 ml 4N sodium hydroxide was added 5 ml acetic acid anhydride. Stirring was continued at 25° C. for 2 h. The precipitate was filtered off and washed with water to give 0.21 g (68%) of 6-acetamido-1-methylquinoxaline-2,3(1H,4H)-dione. M.p. 390° C. NMR (DMSO-d6): 10.1 (1H, broad s), 9.7 (1H, broad s), 7.5-7.0 (3H), 3.43 (3H, s), 2.0 (3H, s).
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