1-Butane sulfonic acid-3-methylimidazolium tosylate, [BSMIM]OTs, is a remarkable catalyst for the cascade synthesis of coumarin-functionalized indole derivatives via a tandem cyclization reaction of aniline and phenylglyoxal monohydrate. This reaction possibly proceeds through imine formation/nucleophilic addition/cyclization. In addition, this method shows lower E-factors. A clean reaction, easily accessible reactants, metal-free and environmentally friendly reaction conditions, and reusability of the catalyst are the notable advantages of this procedure. In addition, molecular docking studies show the theoretical possibility of binding these types of synthesized compounds to key proteins in tumorigenesis.