The arginine/gallic acid-based deep eutectic solvent as a capable catalyst for the green synthesis of pyrano[2,3-d]pyrimidines

A novel arginine/gallic acid-based deep eutectic solvent (ARG/GAL-DES) was prepared by mixing one mole of arginine (ARG) and two moles of gallic acid (GAL) according to the result of the eutectic point phase diagram and heated until a homogeneous, clear liquid was obtained (~ 30 min, ~ 87 °C). The resulting DES was characterized using Fourier-Transform Infrared spectroscopy (FT-IR), 1H NMR, thermogravimetric analysis–differential thermal analysis (TGA-DTA), densitometry, and eutectic point measurements. Then, ARG/GAL-DES was employed as a green and efficient catalyst for the one-pot, four-component synthesis of pyrano[2,3-d]pyrimidines 2(a–n) from barbituric acid, 4-hydroxy-coumarin, morpholine, and various aldehydes under solvent-free conditions at 80 °C. The reactions proceeded with excellent yields, short reaction times, and facile purification.