Title: Visible Light-Mediated Single-Electron Activation of Carboxylic Acids
Abstract: Carboxylic acids are widely abundant feedstocks, and their direct oxidation has enabled a variety of transformations. Because photoinduced electron transfer primarily results in rapid decarboxylation of the resulting acyloxy radicals, diverting these intermediates toward other canonical pathways of heteroatom-centered radicals remains a distinct challenge. Herein, the development of a ligand-to-metal charge transfer (LMCT) promoted intramolecular C–H lactonization of benzoic and aliphatic carboxylic acids is reported. While 1,5-hydrogen atom transfer (HAT) is typically precluded by the rapid rate of decarboxylation of free acyloxy radicals, mechanistic investigations suggest that the key intermediate is instead a metal-stabilized acyloxy radical, thereby circumventing this undesired reaction pathway. In tandem, related pathways of carboxylate oxidation were leveraged towards the design of novel reactions for additive manufacturing (AM). Net-oxidative photoredox transformations of carboxylic acids often employ redox-active metal salts as terminal oxidants, thereby generating stoichiometric zero-valent metal as a byproduct. Recognizing that the production of such metal under mild photochemical conditions addresses a long-standing challenge in the field, this mode of reactivity was explored for the additive manufacturing of metal-organic multimaterial objects from a single resin. |
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