Ring-chain tautomerism imidazolidines

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). 

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... 

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