Visible light promoted formation of N─S bond by photocatalyst Eosin Y

A novel efficient protocol for the synthesis of 5‐imino‐1,2,4‐thiadiazole motif in open air and visible light has been reported. The reaction involves Eosin Y as photocatalyst which is a cost‐effective organic dye. The designed protocol represents a novel, mild, metal free, green strategy for the construction of 1,2,4‐thiadiazole nucleus by intramolecular cyclization via N─S bond formation. The reaction has been carried out under visible light exposure in ethanol: water (4:1) mixture using 2‐aminopyridine and isocyanate as reactants.