Zwitterionic Imidazolium Salt: An Efficient Organocatalyst for the One-Pot Synthesis of 5,6-Unsubstituted 1,4-Dihydropyridine Scaffolds

An efficient, simple and environmentally benign methodology has been developed for the synthesis of 5,6-unsubstituted 1,4-dihydropyridine derivatives by a three-component condensation of beta-keto esters, amines and alpha, beta-unsaturated aldehydes under solvent-free conditions catalyzed by an aprotic imidazole-based zwitterionic salt. The key advantages of this protocol are metal-free reaction conditions, short reaction time, high yields, reusability of the catalyst, and easy work-up. A variety of dihydropyridine derivatives have been synthesized with high yields at room temperature and only water is formed as a green by-product.