Mechanochemical synthesis of pyrrolo[1,2-a]indoles via consecutive C–C and C–N bond formation in the presence of an ionic liquid: antimicrobial and photophysical studies

Abstract

Brønsted acidic ionic liquid (BAIL), 1-butane sulfonic acid-3-methylimidazolium tosylate ([BSMIM]OTs), is an efficient and useful organocatalyst for the two-component reaction of 3-substituted indoles with propargyl alcohols to synthesize biologically active pyrrolo[1,2-a]indole derivatives by the ball-milling technique. This mechanochemical technique has taken the reactions beyond the conventional grinding method to provide good to excellent yields of the corresponding products in a very short time. The catalyst enables the efficient formation of both C–C and C–N bonds under environmentally friendly conditions, conducted neat, without any additional base or ligand. Key advantages of this methodology include its simplicity, the use of easily accessible reagents, a broad substrate scope, and its metal-free, solvent-free, and environmentally friendly reaction conditions. Furthermore, the catalyst can be easily reused, contributing to the overall sustainability of the process. In addition, the present method is also applicable for gram-scale synthesis. This procedure is associated with high EcoScale metrics and a low E-factor. The synthesized compounds exhibited promising biological activities. Antimicrobial activity against various Gram-positive and Gram-negative bacteria was evaluated for some randomly selected synthesized compounds. In addition, we also studied the photophysical behavior of these unique and novel 3H-pyrrolo[1,2-a]indole derivatives.