Studies on Heterocyclic Compounds. XX. The Reaction of the Oxazolo [3, 2-b] pyridazinium Perchlorates with Hydrazines

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On treatment with hydrazine hydrate (80%) and methylhydrazine, oxazolo [3, 2-b] pyridazinium perchlorates (I) furnish hemi-perchlorates of 4H-pyridazino [6, 1-c] [1, 2, 4] triazines (VI) and 1-methyl-4H-pyridazino [6, 1-c] [1, 2, 4] triazinium perchlorates (VIII), respectively. On reaction with phenylhydrazine by refluxing in acetonitrile, I affords an osazone (XII), a phenylazopyridazine (XIII) and its hydrazo derivative (XIV), which are also formed from N-phenylamino-6-chloro-2-phenacyl-2, 3-dihydropyridazin-3-ylideneimine phenylhydrazone (XV) by refluxing with phenylhydrazine in acetonitrile. In the reaction of I with hydrazines, it has been shown that the initial attack of the reagent always occurs at the C_8a-position to furnish various condensed pyridazine derivatives.