Asymmetric Catalytic Ring‐Expansion of 3‐Methyleneazetidines with α‐Diazo Pyrazoamides towards Proline‐Derivatives

Abstract

AbstractWe realized a highly efficient formal [1,2]‐sigmatropic rearrangement of ammonium ylides generated from 3‐methylene‐azetidines and α‐diazo pyrazoamides. The employ of readily available chiral cobalt(II) complex of chiral N,N′‐dioxide enabled the ring‐expansion of azetidines, affording a variety of quaternary prolineamide derivatives with excellent yield (up to 99 %) and enantioselectivity (up to 99 % ee) under mild reaction condition. For the rearrangement of ammonium ylides, the installation of a pyrazoamide group as a masked brick to build chiral scaffolds proved successful. The enantioselective ring expansion process was elucidated by DFT calculations.