Energy-Transfer Excitation of Dibenzothiophene <i>S</i>-Oxide Induces Oxomethylation of Styrenes

The photoexcitation of sulfoxides has traditionally required intense UV light irradiation, thereby limiting their applicability in organic synthesis. Here we report that photosensitization under <i>fac</i>-Ir(ppy)₃ catalysis and blue-light irradiation effectively excites dibenzothiophene <i>S</i>-oxide under much milder conditions. The excited sulfoxide reacts with DMSO solvent to promote the oxomethylation of styrenes. Mechanistic investigations disclosed that the excited dibenzothiophene <i>S</i>-oxide undergoes rapid fragmentation in DMSO to generate a methyl radical, a methylsulfonyl radical, and dibenzothiophene. This process provides a new photocatalytic method to generate a methyl radical without recourse to peroxides or metal oxidants.