Thiazole-carboxylic acids, basicity

The acylation of 5-hydroxymethylimidazo[2,l-h]thiazoles 96 (with, e.g., R = H, R = Ph) has been reported (80FES896). In line with expectations, ethyl esters of imidazol[2,l-6]thiazole carboxylic acids on basic hydrolysis... 

Acidic and basic hydrolysis of ethyl 4-oxo-4//-pyrido[l, 2-u]pyrimidin-3-carboxylates gave 3-carboxylic acid derivatives (OlMIPl). Stirring rerr-butyl ( )-3-(2-hydroxy-8-[2-(4-isopropyl-l, 3-thiazol-2-yl)-l-ethenyl]-4-oxo-4//-pyrido[l,2-u]pyrimidin-3-yl)-2-propenoate in CF3CO2H at room temperature yielded ( )-3-substituted 2-propenoic acid. 

Aldehydes are usually more easily reduced than carboxylic acids, but as in the previous case the aldehyde may exist in aqueous solution predominantly as the hydrate [Eq. (2)]. The hydrates are reduced at more negative potentials than carboxylic acids. Several other systems have been found to behave similarly [16,17] pyridine-2- and -4-carboxylic acid, imidazole-2-carboxylic acid, and thiazole-2-carboxylic acid. In the last case the yield is low due to competing reduction of the ring. Yields of aldehyde are better at low temperatures due to the slowing of the dehydration reaction. In neutral or basic solution there is electroanalytical evidence for dimerization in the reduction of pyridine-4-carboxylic acid [18]. 

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