Recent Developments in the Transition-metal-free Approaches for C- and N-Arylation/Heteroarylation of Indoles

Indole is a privileged heterocyclic scaffold widely prevalent in bioactive compounds, agrochemicals, and advanced materials. Introduction of aryl and heteroaryl groups offers enhanced structural and functional diversity, intriguing a significant interest in the synthesis of aryl-and heteroaryl substituted indoles. However, the emerging cost- and environment-related challenges associated with the popular transition-metal mediated arylations have propelled a surge in the development of sustainable metal-free approaches. This review discusses the recent progress in the transition-metal-free C- and N- arylations of indoles. Various arylation methods using diazonium salts, diaryliodonium salts, aryl halides and other arylating reagents are discussed. The review assesses the capabilities of current metal-free arylation strategies to inspire the discovery of environmentally benign and sustainable C- and N- functionalization strategies.