Imidazolidin-2-ones bicyclic

Similar alkylations may be effected on oxygen. l-(2-Chloroethyl)imidazolidin-2-one (312) when treated with potassium hydroxide or sodium hydride underwent ring closure to the tetrahydroimidazo[2,l-6]oxazole (313) (57JA5276). This approach can be used for the preparation of bicyclic hydantoins and the corresponding dihydro derivatives of (313) using the mesylate of (312) and NaH (77JHC5U, 79JMC1030). 

Bicyclic imidazolidin-2-ones 173 have been prepared in good yields and high diastereoselectivity (Scheme 5.46) [51], The ring closure of MAT -disubstituted ureas 172 was catalysed by [AuCl(lPr)] complex in presence of a silver salt. 

Cyclic amides can be used like the thioamides of the previous section. l-(2-Chloroethyl)imidazolidine-2-one 61 with potassium hydroxide affords the tetrahydroimidazo[2,l-A oxazole 62 (Scheme 38) <1957JA5276>. The bicyclic imidazo[2,l-A]oxazole 64 can be prepared by the cyclization of 63 (Scheme 39) <1999H1081>. A similar methodology was applied to the synthesis of oxazolo[3,2- ]benzimidazole 66 by heating 2-chloro-l-phenacylbenzimidazole 65 with sodium benzoate in DMF (Scheme 40) <2001CHE1179, CHEC-III(11.04.9.1.1)151>. 

Intramolecular reactions of species (69) with simple alkenes have been of great importance in the field of /V-acyliminium chemistry. In Section 4.4.2.2, the mechanistic principles of IV-acyliminium cycliza-tions using these ir-nucleophiles have already been treated. If the carbon-carbon double bond tethered to the nitrogen atom does not have an electronic bias, a considerable preference exists for the formation of a six-membered ring by way of a chair-like transition state. Some recent applications of this reaction type are the preparation of bicyclic imidazolidin-2-ones (equation 57) and a cyclization reaction proceeding via a tertiary iV-acyliminium intermediate generated by protonation of an enamide (equation 58). A third example (equation 59) leads to a bicyclic system that apparently prefers proton loss instead of formation of a tertiary formate. ... 

Bicyclic l,4-imidazolidin-2-ones were unexpectedly obtained [80] during attempts to synthesise penicillins by cycloaddition of ketenes to the thiazoline ester 17 (Scheme 44). This result is reminiscent of the well known rearrangement of penicillins into penillonic acids [88, 82]. 

Bicyclic 1,4-dihydropyridines were successfully synthesized by Li et al. by the reaction of imidazolidine-based enamines 148 with CH acids 146/112 and aldehydes 147/151 in the presence of a weak base (Scheme 13.38) [63]. Cyclization of those products under basic conditions afforded the tetracyclic 1,4-dihydropyildme derivatives 150/153. One year later, this reactions scope was extended... 

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