Thiiranes

Thiiranes are a class of small heterocyclic compounds characterized by a three-membered ring in which one vertex is a sulfur atom and the remaining two are carbon atoms. The parent compound, thiirane (C2H4S), is the simplest member of the family and is structurally the sulfur analog of cyclopropane and the sulfur analog of oxiranes (epoxides) in related chemistry. The ring is highly strained, which drives their reactivity and makes them useful as synthetic intermediates.

Structure and nomenclature continue to focus on the position of substituents around the three-membered ring; the most basic form is 1,2-thiirane, with additional substituents described by standard ring-naming conventions. Substituted thiiranes vary in stability and reactivity depending on ring substitution and the source of sulfur.

Synthesis methods for thiiranes are diverse and depend on the desired substitution pattern. Common approaches include cyclization of precursors that supply both a two-carbon fragment and a sulfur source, such as vinyl sulfides or β-halo sulfides, under conditions that promote intramolecular closure to the three-membered ring. Alternative routes involve rearrangements or transformations of larger sulfur-containing rings that generate the thiirane framework.

Reactivity is dominated by the ring strain that favors ring-opening reactions. Thiiranes readily undergo nucleophilic opening with amines, thiolates, alkoxides, and related nucleophiles, yielding open-chain products that incorporate sulfur functionality. They can also participate in cycloadditions and other transformations that convert the sulfur atom into diverse functionalities.

Applications of thiiranes span organic synthesis as versatile sulfur-containing building blocks. They are used to introduce sulfur into complex molecules, including pharmaceuticals and materials, and as intermediates in routes to more elaborate sulfur-containing frameworks. See also: aziridine, oxirane, thietane.