ABSTRACT A five‐membered ring incorporating two nitrogen atoms, one selenium atom, and two carbon atoms yields four distinct structural isomers: 1,2,3‐selenadiazole, 1,2,4‐selenadiazole, 1,2,5‐selenadiazole, and 1,3,4‐selenadiazole. The chemistry of selenadiazoles remains a vibrant research field due to their promising biological activities and intriguing reactivity. Synthesis of 1,2,4‐selenadiazole and its analogs can be achieved via several routes, including: (i) oxidative dimerization of primary selenoamides using reagents such as iodine, NBS, PhI(OAc) 2 , t ‐butyl nitrite, Oxone, palladium(II) salts, or α‐bromo ketones; (ii) in situ selenoamidation of aryl nitriles followed by oxidative dimerization; (iii) selenoamidation of isocyanides and subsequent cyclization with hydroxyimidamides or imidamides; (iv) 1,3‐dipolar cycloaddition of 1,2‐di(pyridin‐2‐yl)diselane with nitriles or isocyanates; (v) four‐component coupling of isocyanides with 4‐substituted‐1,2‐phenylenediamines.
Helal et al. (2026) studied this question.