Iron(III) Ligand‐to‐Metal Charge Transfer Photocatalysis Platform for CH Alkylation of Heterocycles with Feedstock Carboxylic Acids

The direct CH alkylation of heterocycles is a valuable strategy for modifying pharmaceutically relevant molecules, yet sustainable and broadly applicable methods remain limited. We report a visible‐light‐driven Fe(III)‐ligand‐to‐metal charge transfer (LMCT) photocatalytic protocol that enables efficient decarboxylative CH alkylation of diverse heterocycles using readily available alkyl carboxylic acids as feedstock alkyl sources. The reaction proceeds under mild conditions, utilizing catalytic amounts of earth‐abundant FeCl 3 and a base, with molecular oxygen serving as the terminal oxidant, to achieve C(sp 2 )C(sp 3 ) bond formation. Leveraging the inner‐sphere reactivity of photoexcited Fe(III)–carboxylate complexes, the method accommodates a wide range of alkyl carboxylic acids, including acetic acid, amino acids, natural products, and drug molecules, to provide pharmaceutically relevant alkylated heterocycles. Notably, the catalytic system also enables direct methylation of structurally diverse heterocycles, offering a sustainable and practical platform for targeted molecular diversification in medicinal chemistry.