Ionic Liquid-promoted the Synthesis of Structurally Diverse Pyrans, Pyranannulated Heterocycles, and Spiropyrans

: During the last two decades, non-conventional solvents, especially various ionic liquids, have been utilized as efficient reaction media as they can play a dual role as solvents and promoters. The use of ionic liquids as a medium increases the efficiency of the reactions due to their inherent features like high thermal stability, ability to act as a catalyst, non-volatility, high polarity, reusability, ability to dissolve a large number of organic and inorganic compounds, etc. Under this direction, various structurally diverse ionic liquids have been employed as efficient reaction media for various organic transformations. On the other hand, among many other important synthetic scaffolds, during the last two decades, the synthesis of pyrans, pyran-annulated heterocyclic scaffolds, and spiropyrans have gained huge attention as they possess a wide range of significant biological efficacies, which include antibacterial, anticancer, antimycobacterial, antioxidant, xanthine oxidase inhibitory, etc. activities. Almost every day, many new methods are being added to the literature related to synthesizing pyrans, pyran-annulated heterocyclic scaffolds, and spiropyrans. Among many other alternatives, various ionic liquids have also played an efficient role as promoters for synthesizing structurally diverse pyrans, pyranannulated heterocyclic scaffolds, and spiropyrans. In this review, we have summarized a large number of literature reported during the last two decades related to the ionic liquid-promoted synthesis of pyrans, pyranannulated heterocyclic scaffolds, and spiropyran derivatives.