Iodide Anion Modulates Halide Equilibrium in Cobalt-Catalyzed Cross-Electrophile Coupling to C-(Hetero)aryl Glycosides.

C-(Hetero)aryl glycosides are privileged in pharmaceutical chemistry, yet their stereoselective synthesis remains challenging. We report an iodide-anion-enabled cobalt-catalyzed reductive cross-electrophile coupling of glycosyl chlorides with (hetero)aryl bromides, affording C-(hetero)aryl glycosides with high efficiency and stereoselectivity. Mechanistic studies reveal that iodide modulates halide coordination at cobalt, preventing Co-Cl deactivation and enabling the formation of the active L9-CoI2(II) species. This work establishes iodide as a multifunctional promoter in cobalt-catalyzed C-glycosylation.