2025 Volume 83 Issue 6 Pages 527-538
C-H bond functionalization represents a powerful strategy for the selective introduction of functional groups at specific C-H bonds. This approach prevents the need for prefunctionalization of starting materials, offering superior atom- and step-economy compared to traditional cross-coupling reactions. However, many C-H bond functionalization reactions rely on stoichiometric amounts of additives, such as oxidants, bases, or acids, to effectively cleave an inert C-H bond. This dependency imposes significant challenges to achieving truly atom-economical transformations, such as additive-free C-H bond functionalization. Furthermore, these additives often compromise functional group compatibility, thereby limiting the applicability of these reactions. In this manuscript, I present a novel additive-free C(sp2)-H bond activation methodology employing carboxylic acid anhydrides. The in-situ generation of rhodium carboxylate or carbonate species through the decomposition of carboxylic acid anhydrides plays a pivotal role in facilitating a concerted metalation-deprotonation (CMD) mechanism without the need for external additives. This approach has been successfully applied to various additive-free and related transformations, including alkoxycarbonylation, acylation, alkylation, and arylation. Additionally, we explored 2,4,6-trimethylbenzoic acid-based carbonate anhydride as a novel alkoxycarbonylating reagent, enabling the introduction of alkoxycarbonyl groups with a diverse range of alkyl substituents. During our investigations, we identified the superior catalytic performance of rhodium iodide compared to previously reported rhodium complexes. This paper not only outlines these reactions but also explains their mechanism based on the experimental results.
