Alkyne Oxidation by a Vitamin B2-Based Photocatalytic System with Both H₂O and O₂ as the Oxygen Source

The employment of readily available photocatalysts and green oxygen atom sources is recognized as a promising strategy to develop sustainable catalysis for oxidation reactions. We herein reported a sacrificial reagent-free system consisting of riboflavin tetraacetate (RFT), an ester of natural vitamin B2 as the photocatalyst, and Sc(OTf)₃ and NaCl as the cocatalysts for alkyne oxidation under blue light or even sunlight irradiation to produce 1,2-diketone in which the oxygen atoms were from both water and molecular oxygen, respectively. A major Cl^-/Cl• cycle was proposed to be involved and achieved by the excited [RFT-2Sc³⁺]* complex via single electron transfer for the first time, distinguished from the OCl^- active species by a two-electron process in previous flavin-halide photo-oxidation systems.