Synthesis of New Unsymmetrical 4,5-Dihydroxy-2-imidazolidinones. Dynamic NMR Spectroscopic Study of the Prototropic Tautomerism in 1-(2-Benzimidazolyl)-3-phenyl-4,5-dihydroxy-2-imidazolidinone

Abstract

The acid-catalyzed cyclocondensation in refluxing acetonitrile of aqueousglyoxal with N-heteroaryl-N'-phenylureas 4a-f (heteroaryl = 2-thiazolyl, 2-pyrimidinyl,2-pyrazinyl, 2-pyridinyl, 3-pyridinyl and 2-benzimidazolyl) led to the formation of thecorresponding 1-heteroaryl-3-phenyl-4,5-dihydroxy-2-imidazolidinones 5a-f. All theproducts were characterized by elemental and spectroscopic analyses. The free-energybarrier (∆GP≠for prototropic tautomerism in 1-(2-benzimidazolyl)-3-phenyl-4,5-dihydroxy-2-imidazolidinone (5f) was determined by dynamic NMR studies to be 81 ± 2KJ molP-1

Keywords

• Dynamic NMR
• N-Heteroaryl-N'-phenylurea
• 2-Imidazolidinone
• Glyoxal.