Photo‐ and Cerium‐Mediated C─C Bond Cleavage for the Deconstructive Diversification of Cyclic Acids

Abstract The selective cleavage of inert carbon‐carbon bonds in unstrained rings continues to pose a formidable challenge in chemical synthesis. Current methods for C(sp 3 ) ─C(sp 3 ) bond cleavage are highly limited, typically relying on transition‐metal catalysis to facilitate ring‐opening via small‐ring strain or inducing β‐fragmentation after generating radicals from oxygen or nitrogen atoms pre‐installed in the substrate. Herein, we introduce an effective strategy for the decarboxylative ring‐opening functionalization of α‐trisubstituted carboxylic acids, mediated by both light and cerium. This method enables the ring‐opening of carboxylic acids with ring sizes ranging from 3 to 12 members, allowing the construction of C─CN, C‐halide, C─C, C─Se, and C─oxime bonds. Notably, this reaction does not require the pre‐installation of an oxygen atom in the substrate, as the carbonyl group is derived from atmospheric oxygen. Furthermore, late‐stage modification establishes distally functionalized carbonyl compounds, which serve as versatile synthons for accessing valuable building blocks.