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

Abstract

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.