Imidazole-4,5-diones, tautomerism

Imidazole-4,5-dicarboxylic acids, coupling, 5, 403 decarboxylation, 5, 434 1-substituted synthesis, 5, 468 synthesis, 5, 362, 402, 484 Imidazole-4,5-dione, l-alkyl-2-phenyl-synthesis, 5, 129, 479 Imidazole-2,4-diones tautomerism, 5, 370 Imidazole-4,5-diones tautomerism, 5, 370 Imidazole-2,4-dithione, 5,5-diphenyl-tautomerism, 5, 370 Imidazole-2,4-dithiones tautomerism, 5, 370 Imidazolepropanol synthesis, 5, 486 Imidazoles accelerators epoxy resins, 1, 407... 

Cases in which more than one tautomerizable substituent are present in the imidazole ring are common, but tautomerism studies of such compounds are less so. Work on the hydantoins (imidazolidine-2,4-diones) is not at all definitive UV and IR studies suggest the dioxo form (78), but evidence for the existence of other tautomeric structures (79,80) is not convincing (Scheme 26). ImidazoIidine-4,5-diones also exist as the dioxo forms. NMR studies show that the 2-benzyl derivatives must exist in solution as the NH form (81 R = H, Me), and the methoxy derivatives, similarly, are NH (82) rather than OH (83) derivatives (Scheme 26). 

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