Photoinduced Synthesis of 5-Amino-1,2,4-Thiadiazoles from Amidines and Isothiocyanates

Herein, we report a novel, photocatalyst-free protocol enabling the efficient synthesis of diverse 5-amino-1,2,4-thiadiazoles from readily available benzamidines hydrochloride and isothiocyanates. This transformation proceeds via a cascade C–N/N–S bond formation. Mechanistic studies, including radical trapping experiments, control reactions, and UV–vis spectroscopy, indicate that the key step involves photoinduced oxidation of an in situ-generated thiolate anion, yielding a critical sulfur-centered radical. The reaction exhibits broad substrate scope and excellent functional group tolerance and takes place without the need of any chemical oxidants and catalysts, thus providing a simpler, more cost-effective, and greener synthetic route for the construction of thiadiazoles.