1.2.4- Dithiazolium salts

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. 

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-... 

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

The primary route to 1,3,2-dithiazolium salts involves the cyclocondensation of l,2-bis(sulfenyl chlorides) with trimethylsilyl azide, which is illustrated for benzo-fused derivatives in Eq. 11.11. ° This method can be extended to the synthesis of bis( 1,3,2-dithiazolylium) salts. 

Although benzoxazolium salts are more acidic than their benzothiazol analogs in position 2, isolation of the corresponding dioxa-diazafulvalenes was unsuccessful (72LA126). Comparable to the 1,3-dithiolium- and 1,3-thiazolium salts, 1,2,4-dithiazolium salts yielded on treatment with triethylamine in acetonitrile at 0°C mixed geometrical isomers of the TTDAF... 

In the examples above the sulfur dichloride links together two carbon atoms. It is equally possible to link two nitrogen atoms, as illustrated by the formation of a 1,4,2,3,5,6-dithiatetrazine (25) from a hydrazodicarboxyl-ate ester.30 Amidinium salts afford 1,2,3,5-dithiazolium salts (26).31... 

Substituted thioindigoid dyes are usually obtained via the appropriate benzenethiol in a Heumann-type synthesis. The final cyclisation of the phenylthioglycolic acid derivative can often be achieved in concentrated sulphuric acid or by using chlorosulphonic acid. Several routes make use of the Herz reaction (Scheme 6.22), in which a substituted aniline is converted into the corresponding o-aminothiophenol by reaction with sulphur monochloride followed by hydrolysis of the intermediate dithiazolium salt [47]. After reaction between the thiol and chloroacetic acid, the amino group is converted into a nitrile group by a Sandmeyer reaction. Hydrolysis of the nitrile leads to the formation of the required thioindoxyl derivative. 

Dithiazolium salts 129 were successfully isolated in the reaction of fluorinated enamines with sulfur monochloride yields were high (1993ZOR491 Scheme 64). 

Various mechanisms can be envisaged for the conversion of substituted acetonitriles into dithiazolium salt 145, yet no firm evidence has been given. The first step could be the chlorination of acetonitrile by sulfur monochloiide, as demonstrated for acetonitrile itself (1985CB1632) and for phenylacetonitrile (1939ZOK1329). This could be followed by sulfur monochloride addition to the cyano group, cyclization and ionization (Scheme 75). 

The reaction of 1,4,2-dithiazolium salts with amines also leads to thiadiazoles. Thus treatment of the A,A-diethylamino dithiazolium salt (177) with an excess of hydrazine (Scheme 32) afforded 2,5-bis(diethylamino)-l,3,4-thiadiazole (180) together with thiobenzamide. The mechanism postulated is as follows in the first step, hydrazine causes rupture of the ring to liberate A,A-diethyl-thiosemicarbazide (178) which in turn reacts with another molecule of (177) to give the intermediate... 

Synthesis of 1,2,3-dithiazoles is the most extensively studied. The widely used and very long-known Herz reaction of arylamines with S2CI2 to give benzo-l,2,3-dithiazolium salts (Section 4.11.8.5) has been extended to hetarylamines (Scheme 17). More importantly, a new impetus for its investigation and development was provided when benzo-l,2,3-dithiazolyl radicals were shown by Mayer and co-workers to be intermediates. The reaction in a modified form was transformed by the above authors to an effective method for synthesis of this new class of stable radicals. When applied to acyclic enaminoketones the thiosulfinylamine precursor of the free radical could be isolated (Scheme 18). It was also extended to cyclic and acyclic oximes to afford fused and monocyclic... 

Diaryl-1,2,4-dithiazolium salts (59) are highly reactive 3,5-dielectrophiles and readily interact with nucleophiles, to give a broad variety of heterocyclic compounds (Scheme 3) <82Mi 413-03, 82NKK1518, 85H(23)997>. 

A-Acylthioureas (149) treated with Bt2 or H2O2 in a perchloric acid medium give 1,2,4-dithi-azolium salts (150 X = C104 ) <8575371 >. Oxidation of (149) to the 1,2,4-dithiazolium salts was also carried out electrochemically, the A-acylurea having been isolated as a by-product <91JPR537>. When disulfides (151), obtained by Bt2 oxidation of (149 R = = H), are heated in AcOH 1,2,4-... 

Active methylene compounds attack the more electrophilic C-5 position of 1,4,2-dithiazolium salts (see Section 4.14.2) to give various products as outlined in Scheme 10. The reaction course is greatly affected by the applied conditions (base and solvent used) as well as by the the nature of the substrate itself. 

The presence of PhjP as a base in the reaction of 1,4,2-dithiazolium salts with amino nucleophiles promotes ring fragmentation, probably by attack at the primary adduct yielding (151) and assisting sulfur expulsion as PhjP S (Scheme 22) <88BCJ4043>. 

Of particular interest are some intramolecular cyclizations, which are used for the preparation of dithiazolium salts. There are three different routes all starting from sodium salts of dithiocarboxylic acids (196) (Scheme 33). 

A number of l,4-(oxa/thia)-2-azoles like 5-alkylamino-3-aryl-l,4,2-dithiazolium salts (270) <86JAP(K)6168480) and dithiazolylene derivatives (271) <87JAP(K)52209069> have been patented as useful agrochemicals. For others their suggested applications or activity are specified as detailed below. 

---