Dithiete Cation-Radicals

Radicals Containing a Four-Membered Heterocycle 1,2-Dithiete Cation-Radicals 

Russell and co-workers have obtained cation-radicals in the 1,2-dithiete system. Such radicals are cyclic, conjugated within the heterocycle, and possess (4 -P 1) electrons, with = 1 they are consequently heteroaromatic witliin the definition given in the introduction to Part I. 3,4-Dimethyl-l,2-dithiete cation radical 89 (R = R = Me) was obtained by treatment of acetoin in sulfuric acid with sulfide ion. The radical is persistent at ambient temperature and unaffected by oxygen. This evident stability, and its formation from open-chain precursors to the exclusion of acyclic possibilities such as 90, whose oxygen equivalent exists, implies that aromatic stabilization of 89 and similar radicals is a matter of fact and not merely definition. 

2-dithiete cation-radical ring was incorporated into various structures (e.g., by variation of R and R in 89 and by appending the li,2-dithiete radical structure to various carbocyclic rings as in 91). The conformational dependence of the proton hyperfine splittings was investigated (those given in 91 are in gauss) and the conformational requirements of the dithiete cation-radical moiety explored. 

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The mass spectra of several unsaturated sulfur heterocycles show the presence of 1,2-dithiete cation radicals. 1,2-Dithiete cation radicals also are obtained by treatment of a-hydroxyketones or a-diketones with sodium sulfide, sodium thiosulfate or sodium dithionite, and sulfuric acid. ° Bis(trifluoromethyl)-l,2-dithiete yields a cation radical directly when dissolved in sulfuric acid. ° The electron-spin resonance spectrum of the benzo-1,2-dithiete cation radical (formed in chlorina-tions with sulfur-containing reagents) has been observed.Thermolysis of a 1,4-dithiin may go via a l,2-dithiete. ° ... 

Dithiet cation radicals also may be involved in the mass spectrometric fragmentation of l,3-dithiole-2-thiones and the corresponding 2-ones. Treatment of l,2-bis(trifluoromethyl)dithiet with cyclopentadienylindium(i) gave 1,2-dithiolen complexes and with cyclic phosphines and phosphites, phosphoranes (235)... 

The molecular and electronic structures of cyclic disulfide cation radicals of 1,2-dithietane 6 and 1,2-dithiete 7, and radical cations of 1,2-dithiolane 2 (2a-c represent stable conformations determined in terms of the symmetry restriction of Cs, Cz, and Czv), with emphasis on the nature of a two-center three-electron (Zc-ie) sulfur-sulfur bond have been examined by ab initio molecular orbital (MO) calculations <1997JMT(418)171>. Unrestricted Hartree-Fock (UHF)/ MIDI-4(d) computations showed that this bond in organodisulfide radical cation 2 is shorter in comparison to 1,2-dithiolane 2 and possesses partial Jt-bond character (structure A), as previously implied by electron spin resonance (ESR) spectroscopy <1982JA2318>, which correlates best with the form as the most favorable conformation of the cation radical 2. Contrary to the repulsive S-S interaction in the parent 1,2-dithiolane arising from the lone pairs of electrons, the hemi-7t-bond formed by one-electron oxidation should stabilize the five-membered ring of 2, or, for example, a similar cation radical of LA 3 which is involved in diverse biochemical reactions. 

Tile following schemes cover those methods which were used for the generation of dithiete radical cations. 

Tlie following summarizes g-values and hyperfine splitting values by ( h) and by ( 33s) in natural abundance for the representative 1,2-dithiete radical cations. 

A two-sulphur electrophilic addition to alkynes was reported by Bock and coworkers . The reagent is a mixture of the sulphur chloride S2CI2 and aluminium trichloride dissolved in dichloromethane. Initially, 1,2-dithiete 38 is formed, but in the preparative procedure the isolated product is a mixture of 2,6- and 2,5-di-fcr -butyl-1,4-dithiin (39 and 40). When the reaction is performed under nitrogen in a closed tube, the substituted dithiete is oxidized to its radical cation (equation 23). 

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