Ionic liquids in C–H activation: synthesis and functionalization of heterocycles and carbocycles

Abstract

This review illustrates various roles played by ionic liquids in organic transformations, such as solvents, additives, promoters, electrolytes and catalysts for the synthesis and functionalization of heterocycles and carbocycles through C–H activation reactions. Ionic liquids offer several advantages such as high stability, intrinsic conductivity, non-volatility, and recyclability, making them appealing alternatives to traditional organic solvents in sustainable organic synthesis. Their unique properties enhance reaction performance, as seen with recyclable [EMIM]BF₄ in quinazolinone synthesis and [TMG][CF₃COO] in amide production, direct diarylation of 6,7-benzindoles, regioselective reactions with aryl iodides, catalytic cyclopropanation with tetrabutylammonium acetate (TBAA), and propargylamine synthesis via A³ coupling reactions. The use of functionalized ionic liquids like [Bmim]PF₆ with phosphine-ligated Pd(II) enhances product isolation, facilitates reactions under mild conditions, and promotes reusability, contributing to environmentally friendly pathways. Thus, this review highlights various ionic liquids used in different reactions, emphasizing their benefits in improving yields, solubility, and product separation in catalytic processes.