Catalytic Application of Ionic Liquids for the Green Synthesis of Aromatic Five-Membered Nitrogen Heterocycles

Five-membered nitrogen heterocycles exhibit a diverse range of applications across various fields, including medicine, agrochemicals, and materials science. Worldwide industries have exploited hazardous organic solvents and catalysts to afford key bioactive heterocycles, which in turn have a devastating impact on the aqueous environment. The tremendous rise in environmental contamination has shifted the focus of the scientific community towards sustainable alternatives. In line with this, ionic liquids have received the attention of investigators and are widely preferred in organic transformations as catalysts, solvents, ligands, and co-catalysts. Ionic liquids exhibit superior physicochemical properties, such as non-volatility, excellent conductivity, low vapour pressure, non-flammability, and electrochemical and thermal stability, thereby emerging as a clean and efficient alternative to the hazardous volatile organic solvents. The ionic-liquid-assisted synthetic approach has become a popular, greener method owing to high efficiency and product yield with notable purity. Thus, the present article aimed at highlighting catalytic applications of ionic liquids in the synthesis of aromatic five-membered nitrogen heterocycles such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, and tetrazole. This article will provide an insight into ionic liquids for their further exploration in organic transformations and related applications.