In view of the contradictory results published in the literature concerning the structure of the indoloquinoxalines obtained by condensation of isatin with an unsymmetrical benzene-1,2-diamine, regioselective syntheses of the 1-, 2-, 3-, and 4-aminoindolo[2,3-b]quinoxalines have been developed. With the four derivatives in hand, isomers obtained by direct cyclocondensations starting from amino or nitro substituted benzene-1,2-diamines could be unambiguously identified. The results of these studies show, on the one hand, that some previous findings need revision and, on the other hand, that the 1-amino isomer could be prepared in one step and in 58% yield.The most classical pathway for the synthesis of indolo [2,3-b]quinoxalines consists in the cyclocondensation of an indole-2,3-dione (1) (isatin) with a benzene-1,2-diamine. When unsymmetrical diamines are used (3-or 4-substituted diamines 5 or 2), the condensation may obviously lead to the HETEROCYCLES, Vol. 75, No. 11, 2008 2745 production of structural isomers i.e. a mixture of the 1-and 4-substituted indoloquinoxalines 6-7 in the first case and of the 2-and 3-isomers in the later one 3-4 (cf. Table 1). Some authors claimed that the results can be rationalized according to the mechanism of the cyclocondensation: the more nucleophilic amino group of the phenylenediamine reacts with the more electrophilic 3-carbonyl group of isatin and a subsequent dehydratation between the second amino group and the lactamic carbonyl affords the tetracycle. 2-4 However, several contradictory examples have been published in the literature.Syntheses starting from benzene-1,2-diamines 2 substituted in the 4-position by various substituents, have been claimed to give only the 2-substituted indoloquinoxalines (3, R = NO 2 4 , Cl 5 , F 6 , CF 3 6 , CH 3 7 ), only the 3-substituted isomer (4, R = Cl 8 , COOH 8 ), one isomer whose structure was not specified (R = COOH 9 , NO 2 2 , F 10 , CF 3 11 ) or a mixture of both derivatives (R = OCH 3 12 , CN 13 , OEt 9 ). Drushlyak et al. claimed to have obtained only the 3-nitroindoloquinoxaline (4a) in a three step pathway: condensation of the 4-nitrobenzene-1,2-diamine (2a) with the N-acetylisatin to give the 3-(2-acetylaminophenyl)-7nitroquinoxalin-2-one, deacetylation and subsequent cyclization in boiling acetic acid. 4Under the same manner, from the corresponding 3-substituted benzene-1,2-diamines 5, the preparation of indoloquinoxalines bearing a substituent in the 1-position 6 and in the 4-position 7 has been published (R = halogen 12 , OCH 3 14 , COOH 15 , COOCH 3 13 ).Structural assignments, usually only based on elemental analyses and, in two cases, on melting points 4,9are not convincing. Furthermore, on most cases, when a mixture of isomers was known to be obtained, they were not separable. As an exception, the 1-and 4-methyl esters have been isolated after flash column chromatography on silica gel but have not been unambiguously identified. 13 Regardless, it was not possible to assign structures from 1 H or 13 C NMR spectra to the ...