[C:1]([CH2:4][N:5]1[C:14]2[C:9](=[CH:10][CH:11]=[CH:12][CH:13]=2)[NH:8][C:7](=[O:15])[CH2:6]1)([OH:3])=[O:2].[O-:16][Mn](=O)(=O)=O.[K+]>O.[OH-].[Na+]>[C:1]([CH2:4][N:5]1[C:14]2[C:9](=[CH:10][CH:11]=[CH:12][CH:13]=2)[NH:8][C:7](=[O:15])[C:6]1=[O:16])([OH:3])=[O:2]The procedure of Borthakur, N. et at., Ind. J. Chem. 20B:822 (1981) was adapted. To a stirred solution of 1-carboxymethyl-1,2,3,4-tetrahydroquinoxaline-3-one (15.400 g, 0.075 mol) and sodium hydroxide (5.20 g, 0.13 mol) in water (250 mL), was added gradually, a solution of KMnO4 (20.800 g 0.132 mol) in aq. NaOH (4% w/v, 120 mL) and the dark purple colored solution was refluxed for 4 h, cooled and filtered. The clear filtrate was acidified (pH~2) with concentrated HCl. Filtration under vacuum (water aspirator) afforded 9.200 g (56%, pure by 1H NMR) of 1-carboxymethyl-1,4-dihydro-2,3-quinoxalinedione as a cream colored powder, m.p.>300° C. (decomposes) (lit. m.p.>300° C., Borthakur et al., supra). It was sufficiently pure for use in the next reaction; 1H NMR: δ4.84 (s, 2H), 7.13-7.27 (m, 4H), 12.16 (s, 1H); IR (KBr, cm-1): 3431, 1743, 1687, 1481, 1406, 1393, 1250.
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