Pyrolysis of aryl azides. V. Characterization of phenylazo, benzoyl and formyl as neighbouring groups

Abstract

The enhancements of thermolysis rate of azidobenzene produced by ortho phenylazo, benzoyl and substituents are 21180, 70.0 and 22.8 at 393.2 K (decalin solutions). The same ortho substituents produce much smaller enhancements (169, 8.56 and 10.7 respectively) in the pyrolysis rate of 1-azido-2,4-dibromobenzene. These results are interpreted as steric effects on an electro-cyclic thermolysis mechanism, and are not consistent with the alternative pathway of intramolecular 1,3-dipolar addition which continues to be advocated by Hall and Dolan.