1.4- Dithiins radicals from

Gerson and co-workers ° have formed both cation- and anion-radicals from the heterocycle dithieno[3,4-6 3, 4 -e][l,4]dithiin-l,3,5,7-tetraone... 

An analysis of the ESR spectrum of the dibenzothiophene radical anion46 yields the following hfs (hyperfine splitting) constants (gffuss) 5.16, 4.48, 1.46, and 0.86. The theoretical values based on HMO data for Model A2 are considerably smaller 2.84, 2.48, 1.47, and 0.27, respectively, which led the authors to make spin-density calculations by the Hartree-Fock method. Quite recently, the spin densities have been calculated for Model B (8S = 1, pcs = 0.566),466 and the following constants were obtained 5.03,3.99,0.75, and — 1.23. A study of the ESR spectrum of the radical derived from 2,8-dimethyl-dibenzothiophene permitted the assignment of the lowest hfe constant value to the proton in position 2. In contrast to the dithiins, experimental data for dibenzothiophene radicals are better reproduced by Model B. 

Recently, radical cations of other conjugated sulfur compounds70 have been prepared the radicals derived from 1,4-dithiin (56), 1,4-benzodithiin (57), and three derivatives of radicals 55 and 57. Analysis of the ESR spectra of these derivatives permitted the assignment of hyperfine-splitting constants to the six chemically non-equivalent... 

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... 

The only other simple 1,4-dithiin anion-radical to have been documented is 176. This shows the ESR spectrum expected from four equivalent nitrogen nuclei. (The indicated hyperfine splitting is in gauss.) The authors draw attention to the low -value of 176, indicative of little spin population on S they argue that the conjugation in the radical may well short-circuit the heteroatoms and arise from direct overlap of the ir-systems on carbon, being possible on account of the nonplanarity (folding) of 176. 

Under conditions where the primary electrode product undergoes a slow chemical reaction, that is, ti/2 is of the order of seconds, the value of n determined by a relatively fast technique like LSV may differ from that obtained by a slow experiment like coulo-metry. This type of behavior was observed in the anodic oxidation of 2,3,5,6-tetraphenyl-1,4-dithiin in MeCN [278]. During CV the reversible oxidation to the radical cation is observed. However, when constant-current coulometry was carried out as described earlier, this time at i = 50 mA, 6.44 min was required to oxidize completely 0.1 mmol of the substrate to a product electroinactive in the potential region of interest, indicating an overall two-electron process (Fig. 43). Thus, apparently contradictory results may be obtained due to the difference in time scale between the two types of experiment. 

Dihydroxynaphthalene and 9,10-diacetoxyphenanthrene react with 1,2-diols and 1,2-dithiols in a one-pot synthesis of annulated 2,3-dihydro-1,4-dioxins and -1,4-dithiins (Scheme 26) <04TL1343>. The reaction of 2,3-dihydroxynaphthalene with 1,2-dihalogenated aromatic compounds leads to linearly annulated dioxins of particular interest are tri- and tetra-dioxins and various hetero-fused dioxins e.g. 62 (34%). Several examples yield cation radical salts on electrocrystallisation <04T8899>. Linear arrays of fused pyran-dioxin-cyclohexane rings as found in natural products derived from the milkweed family have been described e.g. 63 <04EJO4911>. 

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