A practical and selective method for the oxidation of thioethers to sulfoxides under visible light irradiation is reported. The reaction is catalyzed by inexpensive and readily available FeBr₃, using molecular oxygen from air as the sole oxidant under mild and clean conditions. A wide range of thioethers can be efficiently converted to the corresponding sulfoxides with high selectivity under low-power (15 W, light dose = 1.29 × 10⁴ J/cm²) blue light irradiation. Mechanistic studies indicate that superoxide radical anions (•O₂⁻) generated under photoexcitation play a key role in the selective oxidation process. This protocol provides a simple and energy-efficient approach for sulfoxide synthesis using an earth-abundant iron salt photocatalyst.
Wu et al. (Fri,) studied this question.