The C₆H₅N energy surface. V. Isomerization of pyridylcarbenes to phenylnitrene–a ¹³C-labelling study

Abstract

5-(2-, 3- and 4-Pyridyl)tetrazoles have been synthesized with a ¹³C- label at the 5-position and pyrolysed at 500-600° under reduced pressure to generate the corresponding pyridylcarbenes. Analysis of the aniline which results from their isomerization to phenylnitrene has been carried out by pulsed Fourier transform ¹³C N.M.R. The results show that, although both the cycloperambulatory (CP) and insertion-extrusion (IEP) mechanisms are operative, the latter predominates to a very great extent. As in the case of tolylcarbenes, this result is ascribed to a kinetic effect, i.e. the (largely irreversible) nitrogen extrusion step which generates phenylnitrene. The preferred modes of isomerization in the pyridylcarbenes are discussed.