Cp*Rh-Catalyzed NH-Indole-Directed C-H Activation/Annulation toward Indole-Fused Polycyclic Compounds

Indole-fused polycyclic compounds, prevalent in bioactive natural products and pharmaceuticals with antiviral, anti-tumor, and antibacterial activities, represent privileged scaffolds in medicinal chemistry. Consequently, the development of efficient strategies remains ongoing. As a powerful complement to traditional multistep approaches, NH-indole-directed C-H activation/annulation, leveraging the inherent directing ability of the indole N-H group, has emerged as a particularly efficient and step-economical approach. This review comprehensively summarizes recent key progress in the synthesis of diverse indole-fused polycycles encompassing [1,2]-, [2,3]-, and [1,7]-fused derivatives through Cp*Rh(III)-catalyzed NH-indole-directed C-H functionalization. The transformations discussed utilize readily available arylindoles and versatile coupling partners such as alkenes, alkynes, diazo compounds, and carbon monoxide, enabling rapid access to structurally complex indole polycycles under generally mild conditions. While significant strides have been made, future challenges including mechanistic elucidation, cost-effective catalyst alternatives, and the synthesis of elusive medium-sized indole-fused rings are also highlighted.