Catalytic indole skeletal editing: atom insertion, atom exchange, and ring-opening reactions

The selective editing of aromatic heterocyclic core skeletons has emerged as a prominent research hotspot and frontier in synthetic organic chemistry over recent years. As one of the most ubiquitous nitrogen-containing heterocyclic motifs embedded in pharmaceutical molecules and natural products, indole also stands among the most widely utilized substrates in the development of novel synthetic methodologies. In the past few years, a large body of studies focusing on the catalytic transformation of the indole skeleton has been successively reported. While several representative review articles have touched upon the topic of indole skeleton editing, the relevant content is usually scattered across different sections of these publications, creating a substantial barrier for readers to systematically and intuitively grasp the full landscape of research progress in this field. Furthermore, these existing reviews generally exclude the ring-opening reactions of indole from their discussion, despite the fact that such transformations constitute a fundamentally important category of skeleton-manipulating reactions. Given the pivotal role of indole in catalytic synthetic chemistry and the continuously growing research attention this field has received, the present article provides a focused overview of catalytic transformations of the indole skeleton. This review covers both classical skeleton-editing strategies and indole ring-opening reactions, with a particular emphasis on summarizing studies that enable the conversion of indole into other heterocyclic compounds, alongside a critical analysis of the inherent advantages and limitations of the corresponding synthetic protocols.