Photocatalytic oxidative cyclization of aromatic thioamides catalyzed by Cu2O rhombic dodecahedra

Cu2O rhombic dodecahedra were used to photocatalyze thiobenzamide cyclization in tetrahydrofuran (THF) forming 3,5-diphenyl-1,2,4-thiadiazole under 390 nm light illumination. The rhombic dodecahedra outperform cubic and octahedral Cu2O crystals. They can also photocatalyze thiobenzamides bearing a wide range of substituent groups with generally high product yields in 18 h at room temperature. Electron, hole and various radical scavenging experiments were performed to support the proposed reaction mechanism. This work demonstrates again that the use of surface-controlled metal oxide crystals offers huge cost advantages over the covalent organic framework (COF) photocatalysts for some organic transformations.