Chiral Macrocycle‐Enabled In‐Situ Trapping of Catalytically Active Peroxometalate Anions for Directing Asymmetric Sulfoxidation

ABSTRACT Herein, we report a strategy employing chiral macrocycles for the in situ trapping of catalytically active anions, enabling highly efficient and enantioselective catalysis. By exploiting the strong anion‐binding ability of tailored bis‐thiourea macrocycles, active peroxotungstate species generated from a Na 2 WO 4 /Na 3 PO 4 /H 2 O 2 system are selectively captured within a confined chiral cavity. Using only 1 mol% macrocycle, sulfide oxidation proceeds efficiently to afford sulfoxides in up to 95% yield and 91% ee. Mechanistic studies identify a macrocycle‐bound phosphato‐bis(oxoperoxotungstate) complex as the key catalytic species. The pronounced macrocyclic effect and the fine stereochemical modulation in response to subtle structural variations underscore the precise control conferred by the confined environment. This work demonstrates that macrocyclic anion trapping can steer the reactivity and stereoselectivity of otherwise elusive polyanionic catalysts—offering a distinct approach that operates beyond conventional cationic ion‐pairing systems. The strategy is expected to be applicable to a wide range of catalytic transformations involving active anionic species.