Oxidative Coupling: An Important Tool for Pyrrole Synthesis

In oxidative coupling, two molecules combine with the help of different oxidants and transition metals. It is used to form various natural and synthetic compounds. Oxidative coupling reactions catalyzed by transition metals (Pd or Cu), Iodine, Cobalt, Ti, etc, are used widely for the synthesis of pyrroles. Pyrrole is a 5-membered heterocyclic ring structure that consists of a single nitrogen. Several methods have been adopted and reported for the synthesis of pyrroles and their analogs in the recent past. Synthesis of pyrrole via oxidative coupling takes place in the presence of various catalysts, bases, and solvents and at different temperatures and times. In another method, Oxidative reactions between diols and primary amines utilizing copper/nitroxyl as the catalyst also yield pyrroles. Rhodium has also been used as a catalyst in oxidative coupling reactions between alkynes and carboxylic acid (substituted by heteroarene or arene) to obtain pyrroles. Paal-Knorr reaction is also one of the most common reactions in the synthesis of pyrrole. In the present study, we summarized different oxidative reactions that have been reported for the synthesis of pyrrole. Hopefully, the study will be helpful for the researchers.