Visible-Light-Mediated Aryl Ketone Coupling with Vinyl Thianthrenium Salts Enables Formal Paternò-Büchi Reactions

Oxetanes are valuable motifs in drug discovery, yet their synthesis from native functional groups remains challenging. The Paternò-Büchi reaction offers a direct approach by oxetane construction from alkenes and carbonyls. However, under visible- light condi-tions this platform remains limited by the high triplet energies of common carbonyls. We report a ketone-alkene coupling strategy that achieves formal Paternò-Büchi reactivity relying on the design principle of alkene radical anion formation from vinyl thi-anthrenium salts. Selective olefin reduction decouples reactivity from carbonyl redox properties, enabling the construction of 2-aryl, 2’-alkyl oxetanes that would otherwise be inaccessible by visible-light-mediated [2+2]-cycloadditions. Initial formation of β-hydroxy thianthrenium intermediates is followed by a subsequent cyclization to give 2,2’-disubstituted oxetanes under mild, visible light-enabled conditions. This approach enables a general blueprint for visible-light-mediated oxetane synthesis beyond the limitations of traditional Paternò-Büchi photochemistry.