NMR-STUDY ON THE TAUTOMERIC EQUILIBRIA BETWEEN THE HYDRAZONE IMINE AND DIAZENYL ENAMINE FORMS IN SIDE CHAINED QUINOXALINES - SOLVENT EFFECTS AND TEMPERATURE-DEPENDENCE

The reaction of ylene-4,5-dihydro-1,2,4-triazolo[4,3-a]quinoxaline 6 w ith 4-ethoxycarbonyl-1-methyl-1H-pyrazole-5-diazonium chloride or 4-cy ano-1,3-dimethyl-1H-pyrazole-5-diazonium chloride gave -ethoxycarbonyl -1-methyl-1H-pyrazol-5-ylhydrazono) xycarbonylmethyl]-1,2,4-triazolo[4 ,3-a]quinoxaline 8a or xycarbonylmethyl]-1,2,4-triazolo[4,3-a]quinoxal ine 8b, respectively, while the reaction of ylmethylene-4,5-dihydrotet razolo[1,5-a]quinoxaline 7 with 4-ethoxy-carbonyl-1-methyl-1H-pyrazole -5-diazonium chloride or 4-cyano-1,3-dimethyl-1H-pyrazole-5-diazonium chloride provided )ethoxy-carbonylmethyl]tetrazolo[1,5-a]quinoxaline 9 a or o)ethoxycarbonylmethyl]tetrazolo[1,5-a]quinoxaline 9b, respective ly. Compounds 8a,b and 9a,b showed the tautomeric equilibria between t he hydrazone imine C and diazenyl enamine D forms in dimethyl sulfoxid e and/or trifluoroacetic acid, and the effects of solvent and temperat ure on the tautomer ratios of C to D were studied by the nmr measureme nts in a series of mixed trifluoroacetic acid/dimethyl sulfoxide media (compounds 8a,b and 9a,b) and at various temperatures (compounds 8a,b ).