Pyrolysis of Aryl Azides. VI. Identification of Neighbouring Group Effects in Pyrolysis of Azidopyridines and Azidoquinolines

Although there are literature reports of anomalous behaviour on pyrolysis of ortho-nitroazido-pyridines and ortho-nitroazidoquinolines, we find that these compounds cyclize to the expected furazan 1-oxides in near-quantitative yields, and with a high degree of neighbouring group participation by the nitro group. Kinetic studies in decalin solution reveal the following rate enhancements by the ortho-nitro group: 3-azido-2-nitropyridine, 466 at least; 4-azido-3-nitropyridine, 5400; 4-azido-3,5-dinitropyridine, 640; 4-azido-3-nitroquinoline, 82.4; 5-azido-6-nitroquinoline, 27.6; 2-nitro-1-azidonaphthalene, 12.7. The unstable furazan oxide, [1,2,5] oxa-diazolo [3,4-c]pyridine 1-oxide, has now been characterized. [1,2,5] Oxadiazolo [3,4-b]pyridine 1-oxide decomposed in decalin at 145° to give products indicative of a nitrene intermediate.