The effect of the p-nitro group on the chemistry of phenylnitrene. A studyvia intramolecular trapping

The photodecomposition of a pyrazolyl substituted p-nitrophenyl azide has b een studied as an intramolecular model for the reactivity of the parent azi de, largely used for photochemical labelling. The singlet nitrene is trappe d by intramolecular cyclization onto the pyrazole nitrogen as well as by th e low yield addition of intermolecular nucleophiles (EtOH, Et2NH). Ring exp ansion to a didehydroazepine is absent. The triplet nitrene abstracts hydro gen (intermolecularly) only slightly more efficiently than the non-nitrated derivative, while it is rather efficiently reduced via electron transfer i n the presence of amines. Hydrogen abstraction is efficient for the excited triplet nitrenes, as revealed by an intramolecular reaction.