Visible Light-Promoted Ir(III)-Catalyzed Stereoselective Synthesis of Azauracil-C-Nucleosides from 1-Bromosugar

A visible light-promoted, mild, and efficient Ir(III)-catalyzed synthesis of <i>C</i>-nucleosides is reported, utilizing 1-bromosugar as the glycosyl radical precursor and 6-azauracil as the nucleobase. The method exhibits high α-selectivity and excellent functional group tolerance. Spectroscopic evidence shows that the coupling reaction happens via initial reductive quenching of the Ir(III) catalyst under visible light. Density functional theory calculation reveals the reason for complete α-selectivity. Finally, biologically active 6-aza pseudouridine analogues were synthesized, making the process a valuable platform for <i>C</i>-nucleosides.