Using Supercritical Diethyl Ether as the Reaction Medium for the Synthesis of 3-Acetyl and 4-Methyl Substituted Coumarins

Due to very good biological activity and use as fluorescent probes, coumarin synthesis and developing new synthesis methods are still an attractive area for many research groups. In this work, for the first time, a novel, mild, and green method has been developed for coumarin synthesis by using supercritical diethyl ether as a reaction medium. The optimum conditions for the synthesis of 3-acetylcoumarins and 4-methylcoumarins have been explored. These newly established techniques could be a favourable approach against two traditional synthetic routes in terms of green chemistry criteria for the synthesis of important intermediates, 3-acetyl coumarins and 4-methyl coumarins. 4-Methyl coumarins have been obtained in good-to-excellent yields (63-87%); for example, bmethylumbelliferone, a naturally bioactive coumarin compound, was synthesised in 30 min at 200oC, resulting in 87% yield, while several 3-acetyl coumarins were synthesized in very good yields (28- 96%).