Iridium‐Photocatalyzed Deoxygenation of Sulfoxides: Competing Oxidative and Reductive Pathways for Thioether Synthesis

ABSTRACT

The deoxygenation of sulfoxides to thioethers is a synthetically valuable transformation, given the ubiquity of thioether motifs in pharmaceuticals, materials, and natural products. However, traditional methods often rely on harsh conditions, stoichiometric reagents, or oxophilic additives, limiting their sustainability and functional group compatibility. Modern methods, relying on photoredox catalysis have since been developed but still require strong oxophilic reagents or high catalyst loadings to circumvent the intrinsic difficulty in the reduction of sulfoxides. Here, we demonstrate that simple iridium‐based photocatalysts can convert both diaryl and aryl‐alkyl sulfoxides into their corresponding sulfides in 17%–95% yields, without the need for oxophilic sacrificial reagents, by finely tuning the reaction conditions. The reaction proceeds under visible‐light irradiation, employing simple amines as sacrificial electron donors and water as a key additive, while tolerating other reducible functional groups such as nitriles and free carboxylic acids. Multidisciplinary mechanistic investigations, combining nanosecond transient absorption spectroscopy, cyclic voltammetry, and density functional theory (DFT) calculations demonstrate that the efficiency of the reaction implies both competing oxidative and reductive quenching pathways of the excited‐state iridium photocatalyst.