Arylhydrazones, dehydration

Thiazole carboxylic acid hydrazides were prepared in a similar way (444, 445). Thus by refluxing thioacetamide or thiobenzamide with y-bromoaceto acetic ester arylhydrazones (83) for several hours in alcohol the 4-carboxythiazole derivatives (84) listed in Table II-ll were obtained (Scheme 36) (656). This reaction is presumed to proceed via dehydration of the intermediate, thiazoline-S-oxide. 

Oximation of dehydro-o- or L-ascorbic acid 2-arylhydrazones 191 followed by dehydrative cyclization and concomitant O-acetylation of the resulting 2-arylhydrazones-3-oximes 192 led to the formation of the 1,2,3-... 

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