Greener Syntheses of Coumarin Derivatives Using Magnetic Nanocatalysts: Recent Advances

Coumarins (2H-1-benzopyran-2-ones) are an important group of biological heterocyclic compounds present in various parts of many plant species, encompassing an array of biological and pharmaceutical activities. In view of the importance of coumarins in heterocyclic chemistry and biological sciences and recent advances in the design of magnetic nanocatalysts, we present herein recent developments pertaining to their synthesis exclusively using magnetic nanoparticles, which can be retrieved easily and thus conform to the tenets of greener synthesis. The preparation of various types of coumarins such as Pechmann-based coumarins, bis coumarins, pyranocoumarins, and coumarin derivatives bearing amine moiety, linked to nicotinonitriles, N-coumarin-2-furanone, and pyrrole-linked chromene derivatives using nanocatalysts with a Fe₃O₄ core are described. This review covers the synthetic developments in the recent years 2012–2021 and focuses entirely on the synthesis of coumarins in the presence of magnetic nanocatalysts using greener approaches such as solvent-free conditions or deploying alternative activation methods, namely microwave or ultrasound irradiation.