Thienothiophenes radicals from

From n -electron calculations, the following order of reactivity of the thienothiophenes 1-3 in free-radical substitution reactions was predicted thieno[3,4-b]thiophene (3) > thiophene > thieno[3,2-M-thiophene (2) > thieno[2,3-6]thiophene (1), the most reactive positions being 2 and S in tiiienothiophenes 1 and 2, and 4 and 6 in thienothiophene 3. ... 

However, experimental studies of the effect upon thiophene or thienothiophenes 1 and 2 of phenyl radicals obtained by thermal decomposition of iV-nitrosoacetanilide, or from aniline and amyl nitrite, demonstrated a somewhat different experimental order of reactivity thieno[3,2-6]thiophene (2) > thiophene > thieno[2,3-6]thiophene (1). It was also found that the phenyl radical preferentially attacks position 2... 

The reduction of thienothiophene 2 with Na-K alloy produced a radical-anion (see Section III,D), and a radical-cation resulted from oxidation with AlCl, in nitromethane or SbCl, in methylene chloride (see Section IV,B 5). No such conversion was observed in the case of thienothiophene 1 this is explained by the extended conjugation throughout the thienothiophene 2 molecide, impossible in thienothiophene 1. 

Ketyls from dicarbonyl compounds in the thiophene series have also been examined. The Bologna group has studied the conformational equilibria in the anion-radical of thiophene-2,5-dicarbaldehyde. They have also investigated the intramolecular cation exchange process within ion-pairs of this ketyl, and of analogous ketyls from the isomeric thienothiophenes, and the consequence for this process of variation in the size of the cation and its complexation by macrocyclic polyethers. The anion-radicals of the isomeric l,2-dithienylethane-l,2-diones (thenils) were recorded several years ago. " ... 

---