Tetracyanoethylene ring closures with

Without additional reagents Ring closures with tetracyanoethylene Double ring closure of nitriles Intramolecular jt4 + jr2-cycloaddition of a cyano group... 

A mixture of a tetrasubstituted thiophene and the ruby-red 1,2-dithiin (59) is formed when thiobenzophenone reacts with tetracyanoethylene in refluxing benzene. It is considered that initial [2-i-2]-cycloadditions involving the C=S and nitrile groups are followed by electrocyclic ring opening and ring closure reactions <97LA1677>. 

Reaction of tetracyanoethylene with (855) occurs by corner attack at C-2 with concomitant cleavage of the C-2—C-4 bond and a-participation by the C-5—C-8 bond to give the dipolar ion (857) ring closure yields (858). The methyl group at C-2 in (856) has a marked influence on the course of the reaction since the adduct isolated had the structure (860). Corner attack at C-4 in this case would give the homoallylic... 

Diederich and coworkers have developed a new class of push-pull chro-mophores resulting from the formal [2-1-2] cycloaddition-retroelectrocyclization (CA-REC) reaction between electron-rich alkynes and electron-poor olefins such as tetracyanoethylene (TCNE) [134]. A highly functionalized 6,6-dicyanopentafulvene 226 with an intense, low-energy charge-transfer band is obtained by a novel ring-closure reaction of a push-pull chromophore 227 (Scheme 6.61a) [135]. Later, they also reported the synthesis of new fulvene-based push-pull chromophores 228 and 229 via the formal [2-1-2] CA-REC reaction of dicyanopentafulvenes 222 and 230 with electron-rich alkynes (Scheme 6.61b,c) [136]. 

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