1.2- Diaminobenzenes, reaction with 1,2-dicarbonyl compounds

The diaminobenzenes (phenylenediamines) are prepared by reduction of 1,3-dinitrobenzene and 2- and 4-nitroanilines. o-Phenylenediamine is of value in the synthesis of a range of nitrogen heterocycles. Thus reaction with organic acids produces benzimidazoles (8). With 1,2-dicarbonyl compounds, quinoxalines (9) are produced. Treatment with nitrous acid results in diazotization of one amino group followed by immediate cyclization to give benzotriazole (10). 

Quinoxalines are products of the spontaneous condensation of 1,2-diaminobenzene (1,2-DAB) with 1,2-dicarbonyl compounds (Scheme 1.1). The reaction was independendy discovered many years ago by Bhnsberg (1884) and Korner (1884). 

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