Dithiole oxidative dimerization

Coupling can also occur via a substituent, as for 1,2-dithiol-3-thiones, which are anodically oxidized to bis(dithiolyium)disulfides [48]. The related a-(l, 2 -dithioT3 -ylidene)acetophenones 16 are analogously oxidized to a di-cation (17) that de-protonates to give the uncharged dimer 18. When, however, the electrolysis was conducted in the presence of an oxidant such as DDQ, or by further oxidizing dimer 18, a new di-cation (19) was formed (Scheme 14) [49]. 

The oxidative dimerization of a,o -dithiols carried out by a large number of oxidizing reagents is a well-known and widely used method for the synthesis of cyclic disulfides. An alternative one-step conversion of the acyclic bisthio-cyanates 297 using TBAF in dry THF at room temperature to form cyclic disulfides in moderate yields, including a limited number of 1,2-dithiolanes 298 (Scheme 54), has been developed <1999TL6489>. The available mechanistic information indicates that the process, induced by so-far-unreported nucleophilic attack by fluoride, tolerates ester and ketal groups, while silyl ethers are cleaved. 

Ethylation of l,2-dithiole-3-thione gives a 3-ethylthio-l,2-dithiolylium ion whose electroreductive dimerization has been investigated. A series of aryl-substituted l,2-dithiol-3-ylidene acetophenones underwent oxidative dimerization via cation-radicals (142) when electrolyzed the dimeric products, which contain a new C—C bond, were elaborated chemically into a series of highly conjugated derivatives including bithiathiophthenes. " ... 

Tetrathianes. (1) Oxidative dimerization of a,a-disuhstituted alkanedithioic acid dianions (Scheme 38) or 1,1-dithiols (Equation 17) - very limited examples and a-monosuhstituted alkanedithioic acids decompose (2) reductive or pyrolytic dimerization of gi OT-disulfenyl dichlorides (Equation 18) - only malonate-derived examples (3) reaction of a-chloro sulfenyl chlorides with sodium trithiocarhonate (Equation 19) - only malonate-derived examples (4) sodium thiophenoxide-catalyzed reaction of thioketones with elemental sulfur (5) reaction of benzo-furan-3(2//)-one with S2CI2" (6) UV irradiation of a CS2 solution of a diazirine (7) reaction of a 2,2,4-trisubstituted-1,3-dithietane with Oxone (Scheme 54)". Method (4) is the most convenient and general of these. 

The use of halogens as two-electron oxidants in oxidative addition to metal centers is well documented. Some examples are the oxidation of a gold(I) dithiolate bridge dimer to a Au(II)-Au(II) species by CI2, Br2, or the conversion of... 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

The oxidative polymerization has been proposed to proceed via a radical coupling that involves the coupling of neutral radicals or cation radicals. The former case corresponds to the oxidative polymerization of phenols and dithiols in which the neutral radical is formed by one-electron transfer after dissociation of a hydron from the monomer, or by the elimination of a hydron after the oxidation. The latter case takes place when the cation radical formed by one-electron oxidation exists as a stable species. The cation radicals then couple with each other, and the dimer is formed through solvent-catalyzed hydron elimination from the intermediate dication. Oxidative polymerization of pyrrole and thiophene uses this mechanism [57-62]. 

Cassipourine has been isolated from Cassipourea species (Rhizophoraceae).8 Wrobel and Glinski have devised a synthesis of racemic material (18).9 The starting material was the / -epoxide (13), which was converted into the three steps (see Scheme 4). Thiobenzyl alcohol reacted regio- and stereo-specifically with this material (14) to give the thiol (15), which oxidized in air to give dimeric products. The racemate (16) and the meso-ioxm were separated by column chromatography. Reduction of the racemate (16) with sodium in liquid ammonia yielded the dithiol (17), which afforded ( )-cassipourine (18) on aerial oxidation. 

Electrochemical oxidation of l,3-dithiol-2-one and -2-thione gave behavior consistent with the formation of dimers which were subsequently oxidized to radicals of uncertain structure. Chemical oxidation of the isoelectronic dithiafulvenes 151 (R = phenyl, 4-chlorophenyl, 4-tolyl, or anisyl) led to dimeric exocyclic C—C-coupled products, indicating the intermediacy of the radical 152. 5o... 

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