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

Abstract:The acid-catalyzed cyclocondensation in refluxing acetonitrile of aqueous glyoxal 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 the corresponding 1-heteroaryl-3-phenyl-4,5-dihydroxy-2-imidazolidinones 5a-f. All the products were characterized by elemental and spectroscopic analyses. The free-energy barrier (∆GPfor prototropic tautomerism in 1-(2-benzimidazolyl)-3-phenyl-4,5-dihydroxy-2-imidazolidinone (5f) was determined by dynamic NMR studies to be 81 ± 2 KJ molP -1 P.

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…OS(O) hydrogen bond [69]. The prototropic degenerated tautomerization of a benzotriazolyl-imidazolidinone derivative 35 (Scheme 5.26) is frozen at room temperature [70]. At higher temperatures, the equilibrium gets fast on the NMR timescale and both the rate constant k T and the free energy of activation G = = 19.3 kcal mol −1 could be determined by dynamic 1 H NMR spectroscopy.…”