An Unusual Thermal Rearrangement of 5,5,6,6-Tetracyano-2-thiabicyclohexane to a Thiophene

Article abstract of DOI:10.1021/jo00206a014

5,5,6,6-Tetracyano-2-thiabicyclo<2.2.0>hexane (2-thiabicyclo<2.2.0>hexane-5,5,6,6-tetracarbonitrile), obtained by cycloaddition of tetracyanoethylene to 2H-thiete at room temperature, rearranges in refluxing benzene to 3-amino-4-cyano-2-(2,2-dicyanovinyl)thiophene <<(3-amino-4-cyano-2-thienyl)methylene>propanedinitrile>.The structure of this product was determined by X-ray analysis.Unusually long S-C and Cα-Cβ bonds (1.742 and 1.429 Angstroem, respectively) are attributed to resonance between the amino group and the dicyanovinyl group.Addition of anthracene to trap dienophiles in the refluxing benzene solution had no effect on the yield of thiophene.In refluxing acetonitrile, only a small amount of rearrangement product is obtained, the major pathway being cycloreversion to thiete and tetracyanoethylene.The latter can be trapped by anthracene, but the thiete polymerizes under the reaction conditions.