A variety of oxazole derivatives that possess an alpha,beta-unsaturated substituent at the 2-position were conveniently synthesized in good yields via a Hantzsch-type reaction between dehydroamino acid amides and P-bromopyruvate derivatives. Furthermore, oxazoles with substituents at the 2- and 5-positions were also obtained in good yields using the corresponding beta-substituted beta-bromopyruvate derivatives. A revised reaction mechanism to explain the enhanced reactivity of dehydroamino acid amides for the Hantzsch-oxazole-type reaction is presented.
Direct palladium-catalyzed alkenylation, benzylation and alkylation of ethyl oxazole-4-carboxylate with alkenyl-, benzyl- and alkyl halides
The ethyl oxazole-4-carboxylate was directly and regioselectively alkenylated, benzylated and alkylated with alkenyl-, benzyl-, allyl- and alkylhalides in the presence of catalytic amounts of palladiumacetate with caesium carbonate using Buchwald's JohnPhos ligand.