The effect of various phenolics in p-tsoh-catalyzed solvent-free microwave-assisted synthesis of 4-methyl coumarin derivatives

Coumarin derivatives from natural and synthetic sources are an important class of heterocyclic compounds that displayed a broad spectrum of pharmacological properties. Among all coumarin derivatives, 4-methyl coumarin has been essentially used as a building block to afford various chemical structures. In this study, the effect of various phenolics and catalytic activity of p-TsOH for synthesizing 4-methyl coumarin derivatives has been investigated under conventional heating and microwave conditions. The highest yield of 4-methyl coumarin derivatives synthesis was achieved using resorcinol (60.10 + 2.9% yield) in the optimum reaction condition of starting materials molar ratio (1:1, resorcinol/ethyl acetoacetate, mol/mol) and 10 mol% of p-TsOH using 800W microwave irradiation at 80^o C for 180s under solvent-free condition. Microwave-assisted condition revealed a useful and simple method to synthesize coumarin derivatives through Pechmann condensation under neat and mild conditions with moderate to high yield, short reaction time, and easier product work-up using organic Brønsted acid catalyst.