Oxidative Synthesis of Kröhnke Pyridines

Oxidative Synthesis of Kröhnke Pyridines

Author: Asian Journal of Organic Chemistry

2,4,6-Triarylpyridines and their derivatives (also called “Kröhnke pyridines”, pictured right) have applications in medicinal chemistry and advanced materials. However, syntheses for this type of compound that are simple, cost-effective, and environmentally benign are still rare.

Kovuru Gopalaiah, University of Delhi, India, and colleagues have developed an efficient iron-catalyzed aerobic oxidative tandem reaction for the synthesis of 2,4,6-trisubstituted pyridines. The approach uses commercially available starting materials such as benzylamines and arylalkylketones, a cheap FeBr2 catalyst, molecular oxygen as a green oxidant, and no solvent.

The reaction has a broad substrate scope and no hazardous byproducts. The proposed mechanism involves an oxidative self-condensation of benzylamine that releases ammonia, a coupling of the resulting imine to the enol form of the ketone reactant, a condensation with ammonia to form the pyridine ring, and a re-aromatization to obtain the desired product.


 

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