Visible-Light-Mediated Photoredox-Catalyzed N-Arylation of NH-Sulfoximines with Electron-Rich Arenes

The direct C-H/N-H dehydrogenative cross-coupling of NH-sulfoximines with electron-rich arenes was realized by oxidative visible-light photoredox catalysis, applying 9-mesityl-10-methylacridinium perchlorate as an organic photocatalyst. Sulfoximines display diverse desirable properties for medicinal chemistry and the pharmaceutical industry. However, their preparation is still challenging. Our reaction proceeds without sacrificial oxidant, at room temperature and is highly selective for the C-N bond forming reaction. The scope of the reaction includes mono- and multi-alkylated and halogenated arenes, which are reacted with aromatic and aliphatic electron-rich and electron-poor NH-sulfoximines, giving moderate to excellent yields of the N-arylated sulfoximines. In addition, we successfully conducted the developed reaction on a gram scale (1.5 g). Mechanistic investigations show that both arene and NH-sulfoximine interact with the excited-state of the photocatalyst. We propose a radical-based mechanism, where both the arene and the NH-sulfoximine are photo-oxidized to their respective radical intermediates. Radical-radical cross-coupling subsequently leads to the N-arylated sulfoximine. Two electrons and two protons are released during the reaction and are subsequently converted into H-2 by a proton-reducing cobalt-catalyst.