1.3.2- Dithiazolium

The thiadiazolo[3,4-g] indole 100 was prepared from 4-amino-5-chlorobenzothiadiazole 99 by treatment with pyruvic acid in the presence of [Pd(But3P)2] (Equation 14) <2004AGE4526>. The Herz reaction of 4-aminoben-zothiadiazole 101 with disulfur dichloride gave the fused 1,2,3-dithiazolium chloride 102, which was condensed with malononitrile to give the ylidene 103 (Scheme 15) <2002J(P1)315>. 

A synthesis of benzofused 1,2,3-dithiazolium (Herz) salts by the action of sulfur monochloride on arylamines is the best-known synthesis of this class. Although it has been known for over 80 years (1922DEP360690), it is still in use. This chemistry was reviewed (1957CRV1011) and therefore here we describe the synthesis of heteroannulated 1,2,3-dithiazolium salts and new achievements in their preparation. 

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 1,2,3-dithiazolium ring is transformed to a thiazole ring by reaction with CS2 which presumably attacks at ring N through its C atom (Scheme 4) <79KGS477>. 

Reagents other than S2CI2 may be used to convert o-mercaptoaminoarenes to the 1,2,3-dithia-zolium system SOCI2 to give 1,2,3-dithiazolium salts <84CHEC-I(6)936> and SCI2 to produce benzo-... 

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. 

Much attention was given in CHEC-II(1996) <1996CHEC-II(4)409> to the synthesis of 1,2,3-dithiazoles. Cyclic and acyclic oximes were found to be important precursors to their preparation. The discovery of 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt 20) from the reaction of commercial and cheap acetonitrile and disulfur dichloride gave strong impulse to the synthesis of various 1,2,3-dithiazole derivatives. Formation of the 1,2,3-oxathiazole ring involved almost exclusively the conversion of m -aminohydroxyl compounds to the A-oxide derivatives. 

In an interesting synthesis of 2-cyano-4,5-dihydro-3//-3,l-benzoxazepine 68 Besson el al. have found that reaction of 2-(aminophenyl)ethanol reacts with 4,5-dichloro-1,2,3-dithiazolium chloride to form a SchifFs base, the anion of which 66 undergoes rearrangement to form the above compound in a Smiles rearrangement involving the formation of the spiro-intermediate 67 (Scheme 7) <97SL704>. 

A mixture of 0.34 g methyl 3-aminocrotonate (3 mmol) and 0.63 g 4,5-dichloro-1,2,3-dithiazolium chloride (3 mmol) in 25 mL dichloromethane was stirred at room temperature for 1 h after which 0.49 mL pyridine (6 mmol) was added. The mixture was stirred for a further 30 min. The product was separated by flash chromatography on silica gel, eluting with dichloromethane/light petroleum (1 3) to give 0.43 g methyl 5-cyano-3-methylisothiazole-4-carboxylate, in a yield of 78%. Colorless crystals can form from dichloromethane-light petroleum, m.p. 55 - 56°C. 

C4H2N3OS3] / CONHj Reduction of the parent 1,2,3-dithiazolium salt with Zn/ ACN EPR/ 295 N(3) 0.878 81Mayl/ 84Mayl... 

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