2.4- Disubstituted imidazole 1-oxides arylation

Treatment of N-acylated a-aminonitriles 1077 with PPh3 and a carbon tetrahalide affords 2,4-disubstituted 5-halo-17/-imidazoles 1078 in good yields. A variety of alkyl and aryl substituents (R and R ) are tolerated. A possible mechanism involves the formation of a novel seven-membered ring intermediate and then elimination of triphenyl-phosphine oxide, as illustrated in Scheme 261 <20040L929>. 

Thiazoles may also be intermediate in some other imidazole syntheses <87CJC282>. Dimroth rearrangement of 5-aminothiazoles ((255), (256)) gives hydantoin analogues <86BSBll29>. While 2,4-disubstituted thiazole A(-oxides are converted by aryl isocyanates into imidazoles, the 2,5-isomers are unreactive (Scheme 191) <82CPB1722>. 

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