[N+:1]([O-:4])(O)=[O:2].S(=O)(=O)(O)O.FC(F)(F)C(OC(=O)C(F)(F)F)=O.[CH3:23][O:24][C:25]1[C:34]([O:35][CH3:36])=[N:33][C:32]2[C:31]([CH:37]=[O:38])=[CH:30][CH:29]=[CH:28][C:27]=2[N:26]=1.[OH-].[Na+]>FC(F)(F)C(O)=O>[CH3:23][O:24][C:25]1[C:34]([O:35][CH3:36])=[N:33][C:32]2[C:31]([CH:37]=[O:38])=[CH:30][C:29]([N+:1]([O-:4])=[O:2])=[CH:28][C:27]=2[N:26]=144 ml of 100% nitric acid, 44 ml of 97% sulfuric acid and 44 ml of trifluoroacetic anhydride are added in succession to a solution, cooled to 0° C., of 22 g (100.8 mmol) of 2,3-dimethoxy-quinoxaline-5-carbaldehyde in 88 ml of trifluoroacetic acid. The mixture is maintained at 0° C. for 2 hours and is then carefully poured onto a mixture of 4N NaOH and ice. The temperature should not exceed 20° C. The mixture is extracted with ethyl acetate. The organic phase is washed with an aqueous 1 N NaOH solution, water and brine and dried over sodium sulfate. Crystallization of the crude product yields the title compound in the form of light-yellow crystals. M.p.: 147-149° C.; TLC (EtOAc/hexane 1:3): Rf =0.25.
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