Oxazoles, synthesis from azides

Rearrangement of alkoxycarbonyl imidazole acryl azides in diphenyl ether at high temperatures afforded imidazo[l,5-c]pyrimidinone or imidazo[4,5-c]pyridinone derivatives <02TL5879>. Efficient synthesis of imidazopyridodiazepines from peri annulation in imidazo[l,2-a]pyridine has been described <02TL9119>. A convenient synthesis of 3,6-disubstituted-2-aminoimidazo[l, 2-a]pyridines has been published <02TL9051>. Novel 2,3-dihydroimidazo[2,l-h][l,3]oxazoles were prepared from intramolecular nucleophilic i/wo-substitution of 2-alkylsulfonylimidazoles <02S2691>. 4,4 -Bi-l//-imidazol-2-ones were efficiently synthesized from 5-amino-ot-imino-1 //-imidazole-4-acetonitriles and isocyanates <02JOC5546>. 

Eguchi and co-workers ° developed a general synthesis of 2,5-disubstituted and 2,4,5-trisubstituted oxazoles from an intramolecular Aza-Wittig reaction of (Z)-p-(acyloxy)vinyl azides (Scheme 1.74). An a-bromoketone 277 was converted to an a-azidoketone 278, which was O-acylated at 78°C to give, exclusively, a (Z)-p-(acyloxy)vinyl azide 279. This was attributed to intramolecular chelation of lithium by the enol oxygen and the a-nitrogen atom of the azide. 

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