Arylnitrenes with nucleophiles

Wolff (1912) was the first to observe the ring expansion of phenyl azide, on thermolysis in aniline, to a compound he called dibenzamil (45). It was many years before this compound was shown to be 2-anilino-3if-azepine. This reaction was also found to take place on photolysis of aryl azides in primary and secondary aliphatic amines. The mechanism that was proposed and which has since been generally accepted involves nucleophilic attack by solvent on a benzazirine, that is believed to be in equilibrium with singlet arylnitrene. Nmr evidence has been advanced for the intermediacy of a 1/f-azepine (46) in related expansions which, as expected, rapidly isomerizes to the more stable tautomer. Spectroscopic evidence is still lacking for the aziridine intermediate 47, but this could simply be due to its short lifetime. On the other hand, the recent work of Chapman and Le Roux discussed in Section 1.4 has brought into question the intermediacy of benzazirine in phenyl... 

It is also known, that ketenimines react with aryl azides, the rate constant of reaction between 51 and 47 is 7.5 x 10 M s. At very low concentration of aryl azides, the lifetimes of 51 and of its 5-iodo derivative was measured to be 4-5rns and 24ms for the 5-methyl derivative (i.e. obs 40-250 s ). The latter values represent the rate of irreversible conversion of ketenimines to triplet arylnitrenes. In the absence of nucleophilic agents, photolysis of aryl azides yields typical products of triplet arylnitrene reactions - azo compounds and anilines in the absence of oxygen and nitro and... 

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