Oxidative Rearrangement Approach for the Ring Contraction of N−H Piperidines to Pyrrolidines

We have developed a method for ring contraction of N− H piperidines using oxidative rearrangement with PhI(OAc) 2 . The reaction forms iminium ion intermediates that are effectively trapped by nucleophiles (e. g., NaBH 4 , H 2 O) yielding the corresponding pyrrolidine derivatives. Additionally, we propose an ionic mechanism supported by experiments and density‐functional theory calculations.