The rearrangement of heteroaryl nitrenes formed by pyrolysis of fused oxadiazolones at 600°C

Heteroaryl nitrenes were formed by pyrolysis of the corresponding ring-fused oxadiazolones at 600°/0.1-0.5 mm with short contact times. 2-Pyridyl and 3-iso-quinolyl nitrenes rearranged predominantly by ring contraction to give cyano-pyrroles and 1-cyanoisoindole, respectively. 2-Quinolyl and 1-isoquinolyl nitrenes underwent ring fission followed by rearrangements which led to O -cyanophenyl-acetonitrile and 4-cyanoindole. 2-Benzo[f]quinolyl nitrene rearranged predominantly by ring fission, but some ring contraction also occurred. The rearrangement of 2-quinolyl nitrene has been investigated by using 14C and 15N labelling. The dominance of ring contraction or ring fission reactions is rationalized in terms of the effect on the whole p-system of the localization of p-electrons in an electrocyclic transition state for ring contraction.