Betaines thiazolium

Fused thiazolium betaines can be prepared from dimercaptoazines, e.g. as in the reaction of the phthalazine (420) <73JAP(K)739lo92>. 

Thiazole A -oxides, A -imides, and A -ylides are formally betaines derived from A -hydroxy-, A -amino-, and A -alkyl-azolium compounds. Where the cation is involved, reactivity is similar to that of thiazolium ions. 

Imidazo[2,l-fc] thiazolium bromides (246) react with ethyl propiolate to give pyrrolo[l,2-a]imi-dazoles (248). The reaction must be carried out in the presence of triethylamine which generates the intermediate betaine (247) as indicated in Scheme 62 <92JOC2347>,... 

Die Unterscheidung verschiedener tautomerer 1,3-Thiazole gelingt mit spektroskopischen oder titrimetrischen Methoden22. N-Substitutierte 1,3-Thiazolium-Salze mit einem aciden Substituenten XH bilden sehr leicht unter Deprotonierung Betaine. 

Dihydroimidazo[2,l-6]thiazolium betaines (71) react with alkynic dipolarophiles to form... 

Dondoni and co-workers conducted a detailed kinetic and spectroscopic study of the reaction of 2-(trimethylsilyl)thiazole 1020 with aldehydes to elucidate the reaction mechanism. They proposed a sequence involving a thiazolium-2-ylide (Scheme 1.273). Thus 1020 was reversibly quatemized with an aldehyde to produce the betaine 1021, which undergoes a C O silyl transfer to generate the... 

Equimolar amounts of imidazoline-2-thione, Hg-bis(phenylacetylide), and phenyl isothiocyanate refluxed ca. 0.5 hr. in pyridine 3-phenyl-7-phenyl(thio-carbamoyl)-5,6-dihydroimidazo[2,l-b]thiazolium betaine. Y 75%. W. Ried, W. Merkel, and S. Park, A. 1975, 79. 

Compounds in which other heterocyclic rings (pyrazoles, isoxazoles, imidazoles ) are fused to thiopyrans have been described. The interesting thiazolium salts (56) were prepared by allowing the betaines (55) to react with 4-thioxothiazolidin-2-ones. Application of the Fischer indole synthesis and the Friedlander reaction to tetrahydrothiopyran-3-one led to the exported indolo-and quinolino-derivatives. Ring closure of (57) under acidic conditions afforded the rearranged product (58). Syntheses of benzothiopyrano[4,3,2-flfe]-quinazolines (59) from 1-amino-thioxanthones and of their S- and 7V-oxides have been described. ... 

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