Oxygen-atom insertion of NHC–copper complex: The source of oxygen from N,N-dimethylformamide

An unprecedented protocol for oxygen-atom insertion reaction of NHC–copper complexes has been developed by employing N,N-dimethylformamide as the oxygen source, which allows the preparation of imidazolinones from carbene complexes and decodes one of the mysterious transformations of NHC–metal complexes as well.