1.3.2- Dithiazolium cations

Dithiazolium cations (343) are easily reduced to the corresponding stable radicals (344) which in turn can be smoothly oxidized back to the cation (84CC573, 85JCS(D)1405, 87CC66,90CB881,92CJC2972). The cations may also be reduced electrochemically cyclic voltametry shows this to be a reversible process. 

Dithiazolium cations can be readily reduced to the stable mono- and diradicals. Reaction of the disalt 43 could be effected, on a milligram scale, by electrolysis in an acetonitrile solution at 50 pA onto Pt wire cathode <1997JA2633>. Larger quantities could be obtained by chemical reduction. Attempts to reduce cation 43 directly with silver or zinc powder were unsuccessful. The most successful approach involved the use of triphenylantimony as reducing agent and bis(triphenylphosphine)iminium chloride ((PPN)Cl Equation (5)). The product obtained (7) is remarkably stable in the solid state, in air, and in organic solutions. 

The Passmore group has developed a synthesis of 1,3,2-dithiazolium cations from alkenes and dithionitronium cation (Equations 20-22). The 2,3-ethylenic bond of 1,4-benzo- and naphthoquinones was also involved in this reaction. 

Dithiazolium cations can be readily reduced to stable radicals. Thus reduction of the disalt 307 by electrolysis or by chemical reduction using triphenylantimony bis(triphenylphosphine)iminium chloride [(PPNC1)] <1997JA2633> gave product 308 which is remarkably stable in the solid state, in air, and in organic solutions. 

The cyclocondensation of trimethylsilyl azide with a bis(sulfenyl chloride) is an efficient synthesis of dithiazolium cations (Section 11.3.5) (Eq. 2.15). ... 

A good method for the preparation of substituted 3,5-diamino-l,2,4-thiadiazoles is the rearrangement of dithiazolium cations with sodium azide <2004HOU277>. If the amino groups at the 3- and 5-positions are different, then a mixture of isomeric 3,5-diamino-l,2,4-thiadiazoles is obtained. 

This methodology has been extended to dithiazolium cations 105 which have been reacted with benzamidine to afford 5-cyano-3-phenyl-l,2,4-thiadiazole 106 in low yield (23% Scheme 12) <1999J(P1)2243>. 

Known 1,2,3-dithiazoles are represented by the structures in row (a) of Figure 1. Strictly, these are 1,2,3-dithiazolines, the first one being 1,2,3-dithiazoline-5-one. 1,2,5-Oxathiazoles are represented by l,2,5-oxathiazolidine-4-ones (b) and 3-methylene 1,2,5-oxathiazolines (c). 1,2,3-Oxathiazoles have been obtained only in the form of their S-oxides (d), which should rather be termed -azolidines and -azolidinones. Experimentally prepared S-oxides of 1,2,3-dithiazoles and 1,2,5-oxathiazoles are depicted in row (e) and should be termed dithiazolines and oxathiazolines. 1,2,3-Dithiazolyl radicals (f) are known, as well as 1,2,3-dithiazolium cations (g) which are the only formally aromatic examples of the ring system and which may be represented by a number of resonance structures (h). 

The reversible electrochemical interconversion of 1,2,4-dithiazolium cation and thioacylthiourea anion was demonstrated by cyclic voltametry (Equation (2)) <91JPR537>. In the presence of chelateforming metals in the form of anions CuCla ", CuBr4, CoCl/ , NiCl/ , etc. the thioacylthiourea anion produced is chelated and the reversibility of the reduction is diminished or entirely blocked depending on the metal. 

Dithiazoles investigated are given in Figure 1(a) these are 1,2,3-dithiazolium cations 1, 1,2,3-dithiazolyl radicals 2, l,2,3-dithiazole-3-ones 3 and related compounds 4, their 2-oxides 5. 1,2,3-Oxathiazoles have been obtained and investigated in the form of their A-oxides (Figure 1(b) and named as cyclic sulfamidates 7 and 8 and sulfimidates 6, 9, and 10. 

Unequivocal evidence was also provided by the in situ 14N NMR spectrum which showed a broad resonance at 8 122.6ppm (Az/1/2 = 1042Hz) indicative of cation 30, and after 6h only one signal was observed at 8 —7.4ppm (Az/y2 = 540 Hz), attributed to the dithiazolium cation 18 <2005CC2366>. 

Subsequent reduction of dithiazolium cation 44 with Na2S204 produced radical 4 in moderate yield (30%) (Equation 6) <2001JMC1992>. 

The synthesis of 1,3,2-dithiazolidines from bis(sulfenylchlorides) and amines has been developed in the 1990s and 2000s (Equations 12 and 14). Trimethylsilyl azide confirmed its important role in the preparation of fused mono- and bis-l,3,2-dithiazolium cations (Equation 18). Oakley and co-workers showed that o-dimercapto derivatives can be used in the synthesis of these compounds if treated with trithiazyl trichloride (Equation 19). Synthesis of iV-substituted 1,3,2-benzodithazole tetraoxide has been successfully carried out from benzene-bis(sulfonylchloride) and aliphatic amines (Equation 15). An important feature in this reaction is the preparation of chiral derivatives from optically pure amines (Equations 16 and 17). 

Rather limited data on ultraviolet (UV) spectra of 1,2-oxa/thia-4-azoles have been published. A comparison of Amax values for 3,5-disubstituted 1,2,4-dithiazolium cations showed that all bands in the UV spectra were strongly influenced by the nature of aryl / zra-substituents <1984CHEC(6)897>. A similarity between the UV spectra of... 

---