Advances in the Synthesis and Reactivity of Selenadiazoles

The four isomeric selenadiazoles comprise five-membered SeN₂C₂ heterocyclic rings and represent a prominent class of organoselenium scaffolds that have received considerable attention in recent years owing to their notable applications in medicinal and materials chemistry. To explore their functionalities, several synthetic methodologies have been developed to diversify these scaffolds with a range of substituents. Cyclization reactions remain the most prevalent approach by employing substituted hydrazines, selonamides, cyano nitriles, and amines under versatile reaction conditions and reagents. This review presents an overview of the strategies reported over the past decade for accessing the four isomeric forms of selenadiazole. The synthetic scope, functionalization and reactivity of the reactions are discussed. Additionally, the non-covalent chalcogen- and halogen-bonding interactions of selected derivatives are reviewed, when present.