Mechanochemical Synthesis and Antimicrobial Studies of 4‑Hydroxy-3-thiomethylcoumarins Using Imidazolium Zwitterionic Molten Salt as an Organocatalyst

Imidazolium zwitterionic molten salt (4-(3-methylimidazolium)­butane sulfonate) has been an efficient and useful organocatalyst for a one-pot three-component reaction of 4-hydroxycoumarin, aldehydes, and thiols to synthesize 4-hydroxy-3-thiomethylcoumarin derivatives by the ball-milling technique. This mechanochemical way has taken the reactions over the conventional grinding method to provide good to excellent yields of the corresponding products in a very short time. All the reactions were carried out under neat conditions, and the coumarin derivatives were obtained without performing any column chromatography. The protocol is beneficial because of mild conditions, a wide substrate scope, product scalability, and the easy product isolation technique. In addition, the present method is also applicable for gram-scale synthesis and shows lower E-factors. The biological activities of the synthesized products are very promising, and the antimicrobial activities have been studied for some randomly taken synthesized compounds.