Mercaptothiazolium Hydroxide Inner Salts

3-Dipolar reactivity of 5-mercapto-THISs has only been demonstrated for 16 (X = S), which, like its oxygen analog, produces with dimethylfumarate, 17. and with phenylisothiocyanate, 21 (25). Compound 16 (X = S) does not react with other typical dipolarenophiles (25). 

5-mercapto-THISs are protonated or alkylated on the exocyclic sulfur atom with simultaneous disappearance of a characteristic long-wave absorption in the ultraviolet region (32. 33). These are stronger for 2 (X = S) than for its 4-aza derivative (33). 

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Mercaptothiazolium hydroxide inner salts (2) (X = S) are prepared from 5-hydroxy-oxazolium inner salts and CS (2, 25). The oxazolium inner salts may advantageously be replaced with their precursors, which are N-arylacylalanins (Scheme 23). 

Maionic add, in monomethine thiazolo-cyanine synthesis, 52 4-Mercaptoimidazolium hydroxide inner salts, from 5-hydroxy THISs, 11 from 5-mercaptothiazolium salts, 12 2-Mercaptoselenazoles. substituted in 4-positions, photographic emulsion, 237... 

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