Visible‐Light Photoredox Catalyzed Facile Synthesis of 2‐Amino‐1,3,4‐Thiadiazoles from Aldehydes and Thiosemicarbazides

A metal‐free, visible light mediated protocol has been developed to synthesize 2‐amino‐1,3,4‐thiadiazoles (ATZ) from commercially available aldehydes and thiosemicarbazides. This one‐pot strategy has been achieved by the condensation of aldehydes with substituted thiosemicarbazides in presence of 2,4,6‐tri( p ‐tolyl)pyrylium tetrafluoroborate (TPP‐TFB) as a photoredox catalyst. Different aldehydes/hetero aldehydes, as well as thiosemicarbazides reacted smoothly under the reaction conditions to afford the 2‐amino‐1,3,4‐thiadiazoles in good to excellent yields. The practicality of the developed protocol has been successfully demonstrated by the facile one‐pot synthesis of commercial herbicide Tebuthiuron on a gram scale. A series of control experiments, cyclic voltammetry, and fluorescence studies have been carried out to support the proposed reaction pathway.