Energy-Transfer Excitation of Dibenzothiophene S-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 fac-Ir(ppy)3 catalysis and blue-light irradiation effectively excites dibenzothiophene S-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 S-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.