Glyoxal with o-phenylenediamines

Quinoxaline has been prepared by the reaction of glyoxal with o-phenylenediamine, and 2-methylquinoxaline by the reaction of pyruvic aldehyde or isonitrosoacetone with < -phenylenedi-amine. 2,3-Pyrazinedicarboxylic acid has been prepared only by the permanganate oxidation of quinoxaline. 2-Methyl-5,6-pyrazinedicarboxylic acid has been prepared from 2-methyl-quinoxaline in the same way. - ... 

The reaction is facile, and it is still the most widely used for the synthesis of both quinoxaline itself and many of its substituted derivatives. The condensation of glyoxal with o-phenylenediamine, followed by sodium carbonate addition, yields quinoxaline in almost quantitative yield.10... 

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