The choline chloride/hydroquinone carboxylic acid-based DES as a novel catalyst for the green synthesis of dihydrochromeno[4,3-d]pyrimidinediones

A novel deep eutectic solvent (ChCl/HCA-DES) was prepared by combining two moles of choline chloride (ChCl) with one mole of hydroquinone carboxylic acid (HCA), based on the results from the eutectic point phase diagram, and characterized by FT-IR, ¹H NMR, TGA/DTA, densitometry, viscometry, and refractive index analyses. Then, it was subsequently employed as an efficient, environmentally friendly and sustainable catalytic system for the synthesis of dihydrochromeno [4,3-d]pyrimidinediones via the three-component condensation reaction of 4-hydroxycoumarin, aromatic aldehydes, and urea at 60 °C under solvent-free conditions. This green protocol offers high yields, short reaction times, and catalyst reusability.