2-Imidazolone ring

Imidazolone ring from o-di-carboxylic acid anhydrides. 

Ring closures of (7-aminocarboxylic acid azides A" -2-Imidazolone ring... 

Dehydration converting the imidazolone ring to imidazolinone seems to be sensitive to the aromatic nature of residue 66 [61, 62]. This step is thought to lead to the formation of an enolate intermediate, which can be trapped by reverse anaerobic chemical reduction of the mature chromophore using dithionite and other reducing agents [63]. 

An azidocarbonyl group undergoes a thermally induced Curtius reaction to an isocyanate, and this reacts readily with a neighbouring primary or secondary amino group to form a fused imidazolone ring. Toluene or diphenyl ether may be used as solvent according to the temperature needed for the reaction to proceed in a reasonable time but without causing decomposition. 

Interesting observations were made in the ionic hydrogenation of imidazolone 627. Reduction of the unacylated imidazolone (R = H) yields a 1 1 (cisjirans) mixture of the saturated product 7. A similar reduction of the diacetyl derivative (6, R = Ac), where the double bond is more reactive because of dearomatization of the imidazolone ring, occurs with a high degree of diastcrcosclectivity. In contrast to the examples above, the c/.v-product is formed preferentially. 

It is interesting that the cleavage of the imidazolone ring occurs non-enzymically by a nucleophylic attack of OH at C-2 whereas the enzymic cleavage, also by a nucleophylic attack, occurs at C-4. 

It is difficult to explain why 1 mole of Os was consumed per mole of hydantoinpropionic acid formed, since the oxidation of the imidazolone ring to the hydantoin ring requires only one atom of oxygen per molecule. Brown and Kies determined that hydantoinpropionic acid was excreted unchanged when administered to experimental animals. This casts doubt on the reported isolation of hydantoinacrylic acid. 

Pinner imidazolone ring synthesis from amidines and benzils... 

Imidazolium salts, di-N-condensed 12, 591 Imidazolone ring opening 15, 313... 

The electrophilic ring opening of iV-allyl HHT 53 with chloroacetyl chloride gave N-allyl- -chloromethyl-a-chloroacetamide 54, which was then alkylated with the diethyl ester of a-aminomethylphosphonic acid (AMPA) to generate the imidazolone 55. Subsequent hydrolysis of 55 gave GLYH3 (57). 

Azolo[l,8]naphthyridines. The reactions of the chloronaphthyridine 229 with o-phenylenediamine at 200 °C and with sodium azide in acetic acid give the fused-ring products 230 and 231, respectively (Scheme 54) <2003IJB192>. Amino acid-substituted naphthyridines can be cyclized to the fused imidazolones 232 upon treatment with phosphorus oxychloride and under microwave irradiation (Equation 62) <2002SC857>. Acylation of 2-hydrazino-naphthyridines followed by heating gives W-acyl compounds which are cyclized intramolecularly to the [l,2,4]tri-azolo[4,3- ][l,8]naphthyridines 233 (Scheme 55) <1996IJB106>. The same compounds may also be obtained from... 

In line with expectations strong acids and bases cleave the oxadiazole ring. After treatment of 23 with 48% HBr an imidazolone-2 (27, R = H) is isolated with cone. HCl 27 (R = NH2) is obtained. Treatment with dilute base (8% KOH) yields compound 28. Compound 27 (R = NH2) is also isolated when 23 is treated with hydrazine hydrate. 

Heimgartner and co-workers conducted a detailed mechanistic investigation of the reaction of [ NJlabeled 2,2-dimethyl-3-(dimethylamino)-27/-azirine 332 with NH-acidic heterocycles (Scheme 6.71). Based on these studies the authors proved that ring opening of 188a with 332 afforded the imidazolone 336 in which... 

Amino acids " " and aminobenzoic acids " " react as nitrogen nucleophiles to effect ring opening of unsaturated 5(4//)-oxazolones. Cyclization of the intermediate acylamino amide has opened the way for the synthesis of new series of imidazolones that now incorporate a carboxylic acid moiety into the N-1 substituent. These compounds are readily further elaborated into derivatives with diverse biological activity. 

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