Benzothiazolium ions

Cationic rings are reduced with the uptake of one electron (e.g., electrochemically) to give neutral radicals. Examples of radicals which have been detected by ESR are 373 and 374. Such radicals, e.g., those 376 from benzothiazolium ions, can dimerize (to 377) or undergo further reduction (to 378) in practice, a mixture of the dihydro derivative 378 and the dimer 377 is obtained. Benzofurazan is reduced polarographically in a six-electron reaction to o-phenylenediamine. 

The mechanism of this interesting reaction is complex. First a carbanion stabilized by conjugation is formed, which, as a strong nucleophile, interacts with a second benzothiazolium ion ... 

By inclusion of the third benzothiazolium ion, further intermediates are formed from the adduct. Fission of a thiazole ring with formation of 2-(ethylamino)thiophenol finally produces the trimethincya-nine. 

As shown in Scheme 2-61, the diazo transfer is a dihydro-de-diazoniation of the azidinium ion leading to the 2-amino-3-ethyl-benzothiazolium ion (4.30). This compound was characterized by Balli et al. (1974 a) as an N-acid deprotonation gives 2-imino-3-ethyl-benzothiazol (4.31). 

Vorsanger, J. J. (1968). Bases derived from 3-methyl benzothiazolium ions. Existence of a heterocyclic carbene. Bull. Soc. Chim. Fr. No. 3, pp. 971-980, ISSN. 0037-8968... 

In C2H5OD and in 0.6 ilf C2H50 -C2H50D exchange was still confined to the 2-position but it was appreciably faster in the more basic medium probably attack of ethoxide ion on both the benzothiazolium cation and neutral molecule is involved. 

An extensive theoretical study of the thiazolium (73), substituted benzothiazolium (74), and benzoselenazolium (75) ions has described well... 

---