Hydrazino compounds, tautomerism

In Scheme B, one molecule of the hydrazino enol (12) tautomerizes to the keto form (15), which reacts with one molecule of phenylhydrazine, giving a hydrazino hydrazone (16) similar to that of Bloink and Pausacker. This tautomerizes to the -ene bis(hydrazino) compound (17), and then loses aniline to afford two isomeric, imino hydrazones (18, 19) which react with a third molecule of phenylhydrazine to give the osazone (14) and ammonia. 

Thioamides react under mild conditions with conjugated azoalkenes (32) to give thiazolines (33) that exhibit hydrazono hydrazino tautomerism. X-ray diffraction studies on (33) showed the compound existed as the hydrazono tautomer <95S1397>. 

This ring system is represented by tricyclic ring system 533 (76JHC1249). Reaction of 3-hydrazino[l,2,4]triazin-5-ones 531 with 3-imi-nobutyronitrile afforded 6-methyl- (or phenyl-) 3-[3-methyl-5-aminopyra-zolyl]-2,5-dihydro[l,2,4]triazin-5-ones 532A, which may exist in tautomeric form 532B. Its reaction with diethoxymethyl acetate (DEMA) or ortho-esters afforded the tricyclic compounds 533. 

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