Synthesis and tautomerism of 2-(3,5-diaryl-1H-pyrazol-4-yl)-1-methyl-1H-benzimidazoles

The cyclocondensation of 1-methyl-2-phenacyl-1H-benzimidazole with aroylhydrazines yields 2-(3,5-diaryl-1H-pyrazol-4-yl)-1-methyl-1H-benzimidazoles. The ¹H NMR spectra indicate that these products display tautomerism. The more stable tautomers have structures containing electron-donor aryl substituents at C-5 and electron-withdrawing aryl substituents at C-3 of the pyrazole ring.