Facile synthesis of biologically important indole based quinoxalines

Abstract

Condensation of 1,2-phenylenediamine with a variety of indole based aldehydes, prepared from the corresponding acid chloride in presence of HSnBu3, furnishes (1H-indol-3-yl)quinoxalines. In addition, 1,2-phenylenediamines substituted with a strong electron-withdrawing group at the para position, provides 6-substituted (1H-indol-3-yl)quinoxalines. Several biologically important quinoxalines were prepared in the same way. The yields are good to excellent in all cases. However, 1,2-phenylenediamine substituted with the weakly electron-donating methyl group, gives an inseparable mixture of 6-methyl and 7-methyl isomers of (1H-indol-3-yl)quinoxaline. All the compounds were characterized by 1 H NMR, 13 C NMR and IR spectroscopy.