Thiaziridines and Thiazirenes

Small rings are associated with distorted hybridization and strain. The presence of a heteroatom coupled with the strain in the system makes the three-membered heterocycles thermally unstable and chemically highly reactive. In particular, thiaziridines and thiazirenes that are stable enough to be isolated have not been synthesized yet. Various attempts to prepare these highly strained heterocycles resulted in products that indicated their transient intermediacy nature. The only known thiaziridines that can be isolated are the substituted thiaziridine-1,1-dioxides possessing bulky tert-butyl(tBu) or adamantly (Ad) groups. Theoretical and computational studies conducted over the past decade implied that the thiazirene ring system lies on minimum potential energy and hence should be stable enough for characterization. The historical inputs by the chemical community regarding thiaziridine and thiazirene systems to understand their nature, properties, reactivity and synthesis are illustrated in this article.