Pyridopyridazines. I. The synthesis and physical properties of Pyrido[2,3-d] pyridazine and Pyrido[3,4d] pyridazine

Abstract

Pyrido[2,3-d]- and pyrido[3,4-d]-pyridazine have been synthesized by removal of hydrazino, chloro, and mercapto groups from the substituted derivatives and by preparation of pyridine-2,3- and -3,4-dialdehydes from the corresponding lutidines followed by condensation with hydrazine. In the latter reaction sequence the side-chain bromination of a 3-alkylpyridine has been achieved. The reaction of hydrazine with aryl o-dinitriles and the oxidation of arylhydrazines have been investigated. The pK_a values, ultraviolet spectra, and infrared spectra of the pyridopyridazines are discussed. No covalent hydration could be detected in either the neutral pyridopyridazines or in their cations.