An efficient PhIO-mediated oxidative C═C bond cleavage and reassembly of enaminone toward oxazolone with high regioselectivity has been reported. DFT calculations revealed that the reaction proceeded through an oxygen atom transfer, C═C bond cleavage, alkylthio migration, and reassembly cascade. This strategy is highlighted by high atom and step economy with formation of five bonds in one pot and generation of a high-valued oxazolone skeleton under mild conditions.