Imidazolidines tautomerism

Imidazole-5-thione, 4,4-diphenyl-tautomerism, 5, 368 3 H-Imidazole-2-thione, 1,3-dimethyl-structure, 5, 367 Imidazole-2-thiones acidity, 5, 367 betaines, 5, 372 synthesis, 5, 481 tautomerism, 5, 367 3H-Imidazole-2-thiones synthesis, 5, 473, 6, 992 Imidazolides deacylation, 5, 453 mass spectra, 5, 360 phosphoric acid reactions, 5, 454 reactions, 5, 451-453 Imidazolidine, l-alkyl-3-phenyl-N-oxidation, 5, 427 Imidazolidine, 1,3-benzyl-2-phenyl-oxidation, S, 427... 

Imidazolidin-2-one, l-(5-nitro-2-thiazolyl)-pharmacological activity, 6, 328 Imidazolidin-4-one, l-aryl-3-phenyl-2-thioxo- C NM S, 355 Imidazolidinones C NMR, 5, 355 Imidazolidin-2-ones nucleophilic displacement, 5, 428 polymers, 1, 279-280 reactivity, 5, 376 synthesis, 5, 466, 471 Imidazolidin-4-ones synthesis, 5, 468 Imidazoline, 2-alkyl-synthesis, 5, 463 Imidazoline, 2-amino-applications, 5, 498 Imidazoline, 2-aryl-synthesis, 5, 463 Imidazoline, 2-methyl-synthesis, 5, 487 Imidazoline, 2-nitroamino-synthesis, 5, 471 2-Imidazoline, 2-arylamino-tautomerism, 5, 368 2-Imidazoline, 1-benzyl-methylation, 5, 425 2-Imidazoline, 1,2-diaryl-synthesis, 5, 463... 

The ring-chain tautomerism of the imidazolidines 279 (80H1313) is of interest (Scheme 99). The isomer ratio is determined by the nature of the substituents and is hardly affected by the polarity of the solvent (CCI4, DMSO). 

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). 

Proton loss from cationic species of type (217 Scheme 116) can give rise to relatively stable imines which can be alkylated or acylated with some facility. However, imines are much more common in compounds which are not in tautomeric equilibrium with fully aromatic imidazoles, and among the imidazolidines. 

Azide-tetrazole tautomerism was discussed in CHEC-I. When imidazolidines react with phenyl-isocyanate the product may be cyclic or acyclic depending on the substituents (see also Section... 

The range of acidic reagents which cleave imidazolidines has been summarized in CHEC-1. The compounds are resistant to cold dilute alkali. Although they are subject to ring-chain tautomerism, the cyclic form is usually dominant. Indeed, with 2-isopropyl-1-methyl- and l-methyl-2-(p-nitrophenyl)-imidazolidines only the cyclic forms exist. In some other analogues evidence of both... 

The fe-carbanions derived from alkyl acetoacetates 17a-e add on the A2-imidazolinium cation 3a to form adduct imidazolidines 18a-e, which could not be obtained in a pure state and were isolated as tautomeric enaminoketoesters 19a e (82TL3301, 83H2129, 85T3345). The formation of homologous enaminoketo-ester 20 from 15 and the fe-carbanion of ethyl acetoacetate 17a is also reported (91T4155). 

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