PIFA-mediated room temperature dehydrogenative annulation for the synthesis of 2-alkenyl oxazoles

The annulation reactions of N-substituted enamides via intramolecular dehydrogenative C-C bond formation has been developed for the synthesis of 2-alkenyl oxazoles with phenyliodine(III) bis(trifluoroacetate) (PIFA) as the only oxidant. The method exhibits excellent synthetic scope at room temperature without using any metal reagent. In addition, the method has been proven to be applicable for the synthesis of aryl oxazoles via the reactions of aroyl-based enamides. The reaction process initiated by the free radical resulting from the homo-cleavage of I-O bond in PIFA has been demonstrated by control experiments.