Oxygenated Thiophene Radicals

Anion-radicals from dithienothiophene dioxides liave been studied (e.g., 121) for which ESR and polarographic results have been presented. Similar results were obtained for certain isomers of 121 but not for others. During electrolytic reduction of deuterated dithienothiophene dioxides, it was found that H-D exchange occurred in the anion-radicals. The source of protons was either impurity from solvent decomposition (DMF) or an adventitious unknown present in acetonitrile. Janssen has also correlated electronic absorption spectra and polarographic reduction potentials with calculated molecular quantities for a wide range of thiophene S,S-diox-ides.  

Katritzky and co-workers described a related benzothienyloxyl 124, prepared by thermolysis of the corresponding 2,2 -dimer. 

These latter workers liave demonstrated, by electrochemical experiments, the different reactivities of 125 and its cis isomer.Thus, whereas 125 is formed essentially reversibly and lost in a slow dimerization reaction and a slow coupling with unreduced thioindigo, its cis isomer is rapidly consumed in isomerization, radical-radical, and radical-parent coupling reactions. Similar differential reactivities with carbon dioxide, acrylonitrile, and cin-namonitrile were also observed. For 6,6 -diethoxytliioindigo, it was found that the electroreduction of the cis and trans isomers occurred at different 

Simultaneously with their work on sulfone anion-radicals, Lucken and co-workers reported ESR and polarographic properties of six isomeric cyclopentadithiophenones (e.g., 126) for which proton hyperfine splittings are indicated in gauss. 

The anion-radical 128 of beiizo[c]thiophene-l,3-dione was observed by ESR spectroscopy several years ago its electronic absorption spectrum has been recorded more recently.  

2-positions, a route presumably sterically impeded in the tert-butyl case. 

Gerdil, Helv. Chim. Acta 56, 196 (1973). ho and M. Matsuda, Chem. Lett., 909 (1974). 

A recent German patent claims oxidative dimerization of substituted 

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When exposed to both light and oxygen, thiophene photo-oxidation can occur [66, 67]. Singlet oxygen formed from photoexcitation, sensitized by the polymer absorption, can then undergo a Diels-Alder 1,4-addition to the thienyl double bonds of the thiophene backbone, breaking the n-electron system. Free radical-assisted chain scission has also been proposed. 

Such nucleophilic displacements are likely to be addition-elimination reactions, whether or not radical anions are also interposed as intermediates. The addition of methoxide ion to 2-nitrofuran in methanol or dimethyl sulfoxide affords a deep red salt of the anion 69 PMR shows the 5-proton has the greatest upfield shift, the 3- and 4-protons remaining vinylic in type.18 7 The similar additions in the thiophene series are less complete, presumably because oxygen is relatively electronegative and the furan aromaticity relatively low. Additional electronegative substituents increase the rate of addition and a second nitro group makes it necessary to use stopped flow techniques of rate measurement.141 In contrast, one acyl group (benzoyl or carboxy) does not stabilize an addition product and seldom promotes nucleophilic substitution by weaker nucleophiles such as ammonia. Whereas... 

Thiophene, dioxirane oxidation, 1156 Thiourea, dialkyl peroxide synthesis, 706 1,4-Thioxane, oxidation, 805-6 Thiyl radicals, triplet oxygen domino reactions, 221-3, 224, 225, 226 THPO (1,2,3,4-tetrahydronaphthyl hydroperoxide), 331-2 Thromboxanes, from arachidonic hydroperoxides, 612... 

Substituted and condensed thiophenes and thiophenols are usually the most abundant sulfur-containing compounds in refined fuels. These compounds are known to react with oxygen to form peroxides and eventually result in color bodies and gumlike fuel deposits. The reaction of thiophenol with a free-radical compound and oxygen is shown below ... 

Benzo[ >]thiophene dianion (173) has been prepared by reduction of benzo[ >J thiophene with sodium metal at - 78°C in [2H8]THF. The H and 13C NMR spectra of the purple solution obtained prove that it is the dianion and not a radical anion. This is the first example of a sulfur-containing (4n)Tr polycyclic dianion. The dianion undergoes oxidation to benzo[ ]thiophene with oxygen (85CC1033). 

Another example of the extmsion of sulfur from a thiaozonide intermediate is given in Section 3.10.2.2. In that sequence, the endoperoxide radical cation resulted from the addition of triplet oxygen to the radical cation of a tetrasubstituted thiophene. 

Some of the most promising alternative candidates were oxygen substituted, for example, for the polymers from monoalkoxy- and 3,4-dialkoxy-substituted thiophenes (see Chapter 3). The oxygen-bearing substituent is able to stabilize free radical and positive charge carrying forms by further delocalization, as depicted in Figures 4.1 and 4.2. 

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