An anomalous course of the reduction of 2-(3-oxo-3,4-dihydroquinoxalin-2-yl)benzene diazonium salt: a reinvestigation

The 1H,13C and 15N NMR spectra of the reduction product of 2-(3-oxo-3,4-dihydroquinoxalin-2-yl)benzene diazonium salt with sodium sulfite were measured and analysed. It is shown that the reaction product corresponds to 1-(indazol-3-yl)-1,2-dihydro-benzimidazol-2-on and not 6H-quinoxalino1,2-c] 1,2,3]benzotriazin-12(13H)-one as published previously. The correctness of the structure was confirmed by an independent synthesis. The observed 15N chemical shifts were compared with the predicted ones using the ACD/NNMR 9.01 program.