Proline-Catalyzed Sequential syn-Mannich and [4 + 1]-Annulation Cascade Reactions To Form Densely Functionalized Pyrrolidines

A highly efficient one-pot [4 + 1]-annulation process for the asymmetric synthesis of densely functionalized pyrrolidine derivatives is described. The in situ generated syn-Mannich adduct obtained via proline catalysis acts as a four-atom component, and Corey’s sulfur ylide or ethyl bromoacetate acts as a one-atom carbon source to construct pyrrolidine units in a highly enantio- and diastereoselective manner.