Synthesis and some reactions of 4-carboxy-2-thiazolylhydrazones

The condensation of thiosemicarbazones with bromopyruvic acid gives thiazolylhydrazone hydrobromides, which were converted to the free bases. The question of the site of protonation was studied by PMR spectroscopy. The possibility of self-protonation in 4-carboxythiazolylhydrazone crystals is not excluded. The thiazolylhydrazones are brominated in the 5 position. Both cyclization to thiazolyltriazoles and the Chetteueya—Walker reaction are realized in the case of oxidation with lead tetraacetate.