Skeletal contraction:A novel strategy to access multisubstituted cyclobutane

The polysubstituted and spirocyclic cyclobutanes were efficiently constructed by the utilization of a novel skeletal contraction strategy which only took one-step synthesis from the readily accessible pyrrolidines.The mechanistic studies indicated that a key intermediate N-aminated pyrrolidine was formed initially and subsequent extrusion of a nitrogen via a radical pathway completed the transformation.This practical methodology was further highlighted by the concise,formal synthesis of the cytotoxic natural product piperarborenine B.