Dithiin oxidative dimerization

The pyridazine dioxide derivative (108) was made by intramolecular nitroso compound dimerization as shown (Scheme 23). 1,2-Oxathiin 2,2-dioxides are obtained by the addition of sulfuric acid to a,(3-unsaturated ketones, e.g. (109) — (110) (66HC(21-2)774). 1,2-Dithiins are synthesized from conjugated diynes using benzyl thiol reductive debenzylation of intermediate (111) by sodium in liquid ammonia at - 70°C gives, after aerial oxidation, the 1,2-dithiin (112) (67AG(E)698). 

The electrochemical oxidation of 2,5-diaryl-1,4-dithiins (50) has been studied using various voltametric techniques and all compounds were found to undergo quasi-reversible one-electron transfers to the radical cations and dications.126 The first formal redox potential and the lifetime of the radical cation were found to decrease with increasing electron donation from the aryl ring. The major products were the 2,2 -dimers, which result via reaction of two radical cations for which rate constants are given. Dibenzothiophene radical cations reacted with tetranitromethane under... 

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 anodic oxidation of a series of 2,5-diaryl-1,4-dithiins (LVIII), as in Eq. (96), has been studied in detail [189]. Cyclic voltammetry (CV) experiments showed that all compounds undergo two quasi-reversible one-electron transfers to form the radical cations and the dications. Linear correlations between E° and a were observed. Preparative electrolyses gave the corresponding 2,2 -dimers (LIX) as the major products in yields up to 20%. The low yields are due to workup difficulties and formation of polymeric materials of unknown composition. 

An interesting feature concerning the redox properties of the complex, [Au(dddt)2] (dddt = 5,6-dihydro-l,4-dithiine-2,3-dithiolate, 3), is that the one-electron oxidized product, [Au(dddt)2]°, can be isolated14. An X-ray analysis of the neutral complex reveals a square planar gold structure stacked in dimeric units as a result of intermolecular S-----S contacts. Extended Hlickel calculations predict that the odd electron resides pri-... 

In acetonitrile there is a reversible one-electron oxidation to the corresponding radical cation at E1/2 = 0.68 V vs SCE. Electrocrystallization of this material generates a dimeric radical cation (39)2"PF6 which shows high electrical conductivity. Cyclic voltammetric studies in acetonitrilerdichloromethane (1 1) on a series of 2,5-di(p-substituted phenyl)-l,4-dithiins have been made [105] and the peak potentials are shown in Table 1. The first oxidation peak is reversible except for thep-MeO derivative which is irreversible as are the second oxidation... 

Dithiins and It4-Di elenins.—1,4-Dithiins (36) are among the photolysis products of biaryl- and benzo-l,2,3-thiadiazoles. The postulated intermediate biradicals (35) dimerize in the direction shown. Thermolysis of cycloalkeno-l,2,3-selenadiazoles produces 1,4-diselenins (37) together with cycloalkynes. A structure determination of 2,5-diphenyl-l,4-dithiin 1-oxide reveals a boat-shaped configuration (Figure) with the sulphur... 

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