Visible-Light-Mediated Decarboxylative Coupling of Aromatic Carboxylic Acids with Aryl Methyl Ketones to Unsymmetrical 1,2-Diketones

A transition-metal-free and operationally simple strategy has been developed for the synthesis of unsymmetrical 1,2-diketones via a visible-light-induced decarboxylative arylation–oxidation cascade. Readily available aromatic carboxylic acids serve as convenient aryl precursors, and Eosin Y acts as an inexpensive organic photocatalyst. Under mild blue-light irradiation (450 nm) at room temperature in PEG-400 and in the presence of air as the oxidant, a broad range of unsymmetrical 1,2-diketones is obtained in good to excellent yields with good functional-group tolerance. Control experiments confirmed the essential roles of light, Eosin Y, and molecular oxygen, and TEMPO inhibition was consistent with a radical pathway. The protocol avoids precious-metal catalysts and stoichiometric oxidants, providing an efficient and practical route to valuable 1,2-diketone scaffolds from abundant starting materials.