Ylides of Thiazolium Ions

Ylides of Thiazolium Ions.—The decarboxylation of thiazolium carboxylates (62) and (64), and parallel work on oxazolium and imidazolium analogues, has been employed for measuring the rate of generation of heterocyclic ylides (63), (65), with the object of studying the effect of the sulphur atom on ylide stability. The kinetic data suggest that the 5-ylides are generated at approximate relative rates of 10 10 1 for the oxazolium, thiazolium, and 

Dehydrothiazole.—The established ready generation of benzyne by the decomposition of benzenediazonium-2-carboxylate has stimulated attempts to produce 4,5-dehydrothiazole analogously, by diazotization of 5-amino-2-methylthiazole-4-carboxylic acid. In the presence of furan, 5-(2 -furyl)-2-methylthiazole-4-carboxylic acid is indeed formed, but the preliminary evidence suggests that 4,5-dehydro-2-methylthiazole in the polar form is unlikely to be involved as an intermediate in this reaction, the product arising more probably from (66).  

Miscellaneous Reactions.—In a study aimed at the elucidation of the mechanism of the decarboxylation of heterocyclic acetic and related acids, compounds (67)—(69) were included in the quantitative experiments. The 

Further examples of the aminolysis of 4-amino-2,3-diarylthiazolium chlorides have been examined [e.g. (70)- (71) and (72) at 50 °C, (70)— (72) at 100 °C]. Taken as a whole, the observations have not sustained the mechanism previously suggested (these Reports, Vol. 2, p. 601), and other proposals have accordingly been made.  

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