Coumarin derivatives (coumarins) are a class of compounds with a wide range of biological activities, which have found their application in medicine, pharmacology, cosmetics and food industry. Coumarin is found in a number of plants such as tonka beans and vanilla grass, among others. The biological activity and potential application of coumarins is highly dependent on their structure. Therefore, many researchers have been performing the synthesis of coumarin derivatives on a daily basis. High demands for their synthesis often result in an increased generation of different waste chemicals. In order to minimize the utilization and generation of toxic organic substances, green synthetic methods are applied in this manner. These methods are receiving more attention in the last few decades.
Green chemistry methods include the use of ultrasound and microwaves, ionic liquids and deep eutectic solvents, solvent-free synthesis, mechanosynthesis and multicomponent reactions. All typical condensation reactions for coumarin synthesis such as Knoevenagel, Perkin, Kostanecki-Robinson, Pechmann and Reformansky reactions, have been successfully performed using these green synthetic methods, which as the term suggests, are also environment friendly. This review presented by researchers from the Josip Juraj Strossmayer University of Osijek, Croatia, is a compilation of the green synthetic methods used in the synthesis of coumarin derivatives. "These methods reduce the utilization and generation of toxic chemicals, and they can also enhance the reaction performance in terms of product yields, purity, energy consumption and post-synthetic procedures when compared to the conventional methods.," says co-author Prof. Maja Molnar. This review provides a first full literature overview on the application of green synthetic methods in the coumarin synthesis, which according to the authors was prompted due to the significance of coumarins as biologically active systems and the recent demands of reducing toxic solvents, catalysts and energy consumption.
The review gives an overview of academic research between the years 1995-2019. "There are some reviews on the coumarin synthesis, but most of them cover only specific reactions on coumarin synthesis and none of them the whole range of green chemistry methods," adds Molnar. "The importance of this work is its comprehensive literature survey on a specific class of heterocyclic compounds, and those researchers working on the coumarin synthesis can find very useful information on the green synthetic approaches."
Keywords: Coumarin derivatives, green methods, deep eutectis solvents, ionic liquids, solvent-free, mechanosynthesis.
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Current Organic Chemistry