Unsaturated cyclic compounds possessing disulfide linkage

Unsaturated cyclic compounds possessing disulfide linkage, such as 1,2-dithiete, 1,2,5,6-tetrathiocin, 1,2,5,6,9,10-hexathiacyclododeca-3,7,11-triene and 1,2,5,6,9,10,13,14-octathiacyclohexadeca-3,7,11,15-tetraene, can be synthesized and isolated. Crystal structures of 1,2-dithietes show planar geometry for the dithiete rings. The structures of 1,2,5,6-tetrathiocins show chair or twist conformation in their crystalline states due to fused or non-fused structure of the tetrathiocin rings, and the 16-membered cyclic compound shows cage structure having cavity in the molecule. Ring conversion reaction takes place among the cyclic compounds under various conditions. The ring-size selectivity of the ring conversion reactions is found to be due to ring strains of the compounds on the basis of ab initio MO calculations. Reactions of 1,2-dithietes with alkenes yield the cycloadducts stereospecifically, and it is found to be reverse electron demand hetero Diels–Alder reaction between ethane-1,2-dithiones, valence isomers of the 1,2-dithietes, and the alkenes by experimental and theoretical studies.