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温度

0 °C

The method of Cheeseman, supra. was adapted. 5,7-Dibromo-1,4-dihydroquinoxaline-2,3-dione (74 mg, 0.23 mMol) was dissolved in concentrated H2SO4 (1 mL) at 0° C. for 30 mins., and then KNO3 (28 mg, 0.27 mMol, Baker) was added to this solution. The mixture was stirred at 0° C. for 3 h and then at room temperature for 30h. It was poured into ice water (8 g) and the precipitate was collected by filtration, was dissolved into 1N KOH (5 mL), and the red precipitate was removed by filtration. The solution then was acidified to pH=2 with 4N HCl to obtain a cream precipitate, which was collected by filtration, then was dried in the air at 50° C. for 4 h, affording the pure 6-nitro-5,7-dibromo-1,4-dihydro-2,3-quinoxalinedione (71 mg, 84.5%), as a yellow powder; mp: 318°-20° C. (dec.). IR (KBr, cm-1): 3468, 3131, 3062, 2931, 1712, 1593, 1537. NMR (1H, DMSO-d6): δ 7.392 (s, 1H), 11.566 (s, 1H), 12.274 (s, 1H). HRMS: calcd. for C8H3N3O4Br2 m/z: 362.8489, found: 362.8478.

1. waitat room temperature for 30h
2. filtrationthe precipitate was collected by filtration
3. dissolutionwas dissolved into 1N KOH (5 mL)
4. customthe red precipitate was removed by filtration
5. customto obtain a cream precipitate, which
6. filtrationwas collected by filtration
7. customwas dried in the air at 50° C. for 4 h