Carbon‐13 nuclear magnetic resonance study of a new ring‐chain tautomerism of some pyridazine derivatives

Abstract

AbstractThe 13C NMR spectra of a number of pyridazine derivatives have been recorded in DMSO‐d6 solution and analysed. Examination of the most diagnostic resonances, with particular emphasis on those arising from the pyridazine ring system, enabled the ready establishment of the presence of a ring‐chain tautomerism in 5‐(o‐aminophenylcarbamoyl)pyridazine‐4‐carboxylic acid, methyl 5‐(o‐aminophenylcarbamoyl)pyridazine‐4‐carboxylate, 5‐(o‐aminophenylcarbamoyl)‐3,6,‐dimethylpyridazine‐4‐carboxylic acid and 5‐(2‐amino‐1,2‐dicyanovinylenecarbamoyl)pyridazine‐4‐carboxylic acid. This gave rise to 3′,4′‐dihydro‐3′‐oxospiro[pyridazine‐5(2H),2′(1H)‐quinoxaline]‐4‐carboxylic acid, methyl 3′,4′‐dihydro‐3′oxospiro[pyridazine‐5(2H),2′(1′H)‐quinoxaline]‐4‐carboxylate, 3′,4′‐dihydro‐3′‐oxo‐3,6‐dimethylspiro[pyridazine‐5(2H), 2′(1′H)‐quinoxaline]‐4‐carboxylic acid and 5‐oxo‐2,3‐dicyano‐1,4,8,9‐tetraazaspiro[5.5]undeca‐2,7,10‐triene‐11‐carboxylic acid, respectively.