Ring-Expanding Reaction of Cyclopropyl Amides with Triphenylphosphine and Carbon Tetrahalide

We succeeded in activating cyclopropyl amides (monoactivated cyclopropane) through the corresponding imidoyl
halides prepared in situ in the presence of 2 equiv of PPh3
and 1 equiv of CX4, and the ring-expanding products (N-substituted pyrrolidin-2-ones) were obtained in good yields.
The reaction mechanism was investigated on the basis of
oxygen-18 tracer experiment.