Tautomerism of guanidines studied by 15N NMR: 2-Hydrazino-3-phenyl-3H-quinazolin-4-ones and related compounds

ORGN 782

Bahaa El-Dien M. El-Gendy, bahaa@ufl.edu, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200

15N NMR spectroscopy is demonstrated to be a powerful technique for discrimination between tautomers which differ in the nitrogen carrying the exchangeable proton since a large chemical shift difference is expected for this nitrogen between the two tautomeric forms. [2-(Substituted)hydrazono]-3-phenyl-2,3-dihydroquinazolin-4(1H)-one 11a-i are shown by 15N NMR to exist in DMSO solution predominantly as the imino tautomers B and not the amino tautomer A. 4-[(2-(1H-benzo[d]imidazol-2-yl)hydrazono)methyl]-N,N-dimethylaniline 12 and 3-[2-(4,6-dimethylpyrimidin-2-yl)hydrazono]-1-methylindolin-2-one 13 were found to exist predominantly as the amino tautomers. The X-ray structure of compound 11b demonstrated the imino tautomer in the solid state also.