Sulphur walk

The sequential order of the ring carbons is preserved, leading to the suggestion that the reaction proceeds via a sulphur walk . In support, a small amount of the cyano thiophene valence tautomer 2-cyano-3-methyl-5-thiabicyclo[2.1.0]pent-2-ene (133) was isolated from... 

Apart from hydrodesulphurization, reactions causing transformation or destruction of the thiophen ring are rather rare. Three interesting examples have been reported. In the first, photolysis of 3-cyanothiophen (22) in furan affords the adduct (23) as the major product. 2-Cyanothiophen behaves in a similar way, and an analysis of permutation patterns has indicated that there is a mechanism involving first the 2,5-bridged compound (24) followed by a walk of the sulphur atom. Anils (25) are converted into pyrroles (26) by triethyl phosphite a similar ring-opening by intramolecular insertion of nitrene has also been shown to occur with o-nitrophenyl-di-(2-thienyl)methanes. ... 

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