Flavoenzyme‐inspired Reductive Dehalogenation of α‐Br and α‐Cl Carbonyl Compounds with Riboflavin Tetraacetate as Photocatalyst

Reductive dehalogenation represented a straightforward way to the breakage of carbon‐halogen bonds, exerting great significance in organic synthesis and potential in environmental decontamination. Riboflavin, a small molecular, photosensitive, and redox‐responsible coenzyme in both oxidases and reductase, has inspired various biological and biomimetic photocatalytic oxidations but a few biocatalytic reductions. Herein, we described a visible‐light‐induced reduction of C‐Br and C‐Cl bonds to form C‐H bonds using riboflavin tetraacetate (RFT) as a flavoenzyme‐inspired photocatalyst. The halogen atoms of α‐bromo‐ and α‐chloro carbonyl compounds could be smoothly removed at room temperature with triethanolamine as a suitable terminal reductant and a sustainable solvent system consisting of ethanol and water. A series of deuterium isotope labeling experiments indicated that the hydrogen atom sources of the dehalogenated products should be water, reductant, and the hydroxyl group rather than the α‐hydrogen atom of the alcoholic solvent. Other control experiment and UV‐Vis studies suggested the single electron transfer process between the excited photocatalyst and the reductant, the reduced photocatalyst and the C‐X bond, respectively. This work further tapped the versatile capacities of riboflavin‐based photocatalysts in chemical reductions more than conventional oxidative reactions.