Japp‐Klingemann Reaction

Abstract

The reaction between aryldiazonium salt and compounds with methylene protons activitated by electron‐withdrawing groups in which at least one of such activating groups is an acyl, carboxyl, or ester group to form an unstable azo intermediate that rearranges into a stable hydrazone derivative by expelling of the above acyl, carboxyl or ester group is known as the Japp–Klingemann reaction. The study finds that this reaction occurs at very mild and almost neutral conditions, with an optimal pH of 6.2. Particularly, under the alkaline conditions or when an excess of diazonium salt is used, the second diazonium ion can couple to the generated hydrazone. The modification of reaction has been tried through the treatment of acidic diazonium salt with sodium acetate before the addition of compounds with active methylene groups. Additionally, this reaction has been carried out in the presence of an ammonium salt to promote the coupling rate. This reaction has been applied to synthesize a variety of amino acids, nitrogenous heterocycles and tetrahydrocarbazole derivatives.