Graebe‐Ullmann Synthesis

Abstract

The preparation of carbazoles involving the pyrolysis of 1‐phenyl‐1,2,3‐benzotriazole prepared from ortho ‐amino‐diphenylamine and nitrous acid is known as the Graebe–Ullmann reaction. It is known that this reaction involves the cyclization of a diradical or iminocarbene intermediate to 4aH‐carbzole, which isomerizes to carbazole via a [1,3] hydrogen shift. This reaction has been modified using microwave irradiation. The importance of this reaction has been evidenced in the preparation of carbazole derivatives.