The effect of the p-nitro group on the chemistry of phenylnitrene. A study via intramolecular trapping
The photodecomposition of a pyrazolyl substituted p-nitrophenyl azide has been studied as an intramolecular model for the reactivity of the parent azide, largely used for photochemical labelling. The singlet nitrene is trapped by intramolecular cyclization onto the pyrazole nitrogen as well as by the low yield addition of intermolecular nucleophiles (EtOH, Et2NH). Ring expansion to a didehydroazepine is absent. The triplet nitrene abstracts hydrogen (intermolecularly) only slightly more efficiently than the non-nitrated derivative, while it is rather efficiently reduced via electron transfer in the presence of amines. Hydrogen abstraction is efficient for the excited triplet nitrenes, as revealed by an intramolecular reaction.