The reaction of NH-indazoles with 1-fluoro-2,4-dinitrobenzene: the unusual formation of benzotriazole-N-oxides

When N-unsubstituted indazoles, like indazole itself, reacted with 1-fluoro-2,4-dinitrobenzene or 1-chloro-2,4,6-trinitrobenzene, three products were obtained whose structures were determined by X-ray diffraction. Besides the two N-substituted nitroaryl derivatives, a third compound was obtained with the same molecular formula (C13H8N4O4) to which was assigned the structure of a derivative of benzotriazole N-oxide. With the combined use of crystallography, NMR and DFT calculations this reaction was studied with special stress on the mechanism of formation of the benzotriazole-N-oxide.