A Comprehensive Review of Developments in the Synthesis of Isoindoloindolones and Indenoindolones: Mechanisms and Synthetic Strategies

Abstract The isoindoloindolone and indenoindolone scaffolds are structurally distinct and synthetically versatile polycyclic indole derivatives that have gained significant attention in medicinal and synthetic organic chemistry. These fused‐ring systems combine the pharmacophoric indole core with extended conjugation, imparting diverse biological activities and improved physicochemical properties relevant to drug design and functional materials. Over the past two decades, numerous synthetic approaches have been developed to access these motifs, yet the methods remain scattered across the literature. This review categorizes all reported protocols since 2002 into four major groups: (i) transition‐metal‐catalyzed strategies, mainly Pd‐, Rh‐, and Cu‐catalyzed annulations, carbonylations, and C–H activations; (ii) Lewis‐acid‐catalyzed condensations of indoles with aldehydes, ketones, or alkynes under metal‐free conditions; (iii) base‐mediated, metal‐free approaches employing SNAr, benzyne, or enolate chemistry; and (iv) one‐pot domino sequences, including ionic, oxidative, or reductive cascades and hypervalent‐iodine‐promoted annulations, emphasizing atom economy and operational efficiency. Each section summarizes representative substrates, reaction conditions, and mechanistic insights, enabling direct comparison of catalyst performance and synthetic scope. This comprehensive review unifies two decades of dispersed studies, providing a concise reference for chemists developing fused‐indole architectures.