Dedicated to Professor Wei-Yuan Huang on the occasion of his 85th birthday
The 1,3-dipolar cycloaddition of azomethine ylides to electron-deficient alkenes is one of the most powerful methods for the construction of highly substituted pyrrolidine rings. [1] Following early research on the preparation of optically active pyrrolidines in the presence of either a stoichiometric amount of a chiral metal complex [2] or a chiral auxiliary, [3] an asymmetric catalytic version of this reaction has been developed recently. [4][5][6][7][8] The groups of JΓΈrgensen, [4a] Zhang, [5a] Schreiber, [6] Zhou, [8a] and Carretero [8b] have reported that the reaction of glycine derivatives with electron-deficient alkenes is highly enantio-and endo-selective in the presence of chiral Zn II -bisoxazolines, Ag I -phosphanes, Ag I -quinap, Ag-P,N ligands, and Cu-fesulphos, while the groups of Komatsu and Zhang have reported exo selectivity with a Cu-diphosphane complex and P,N ligands as catalyst. [5b, 7] Each of these reactions involves derivatives of unsaturated carboxylates as the dipolarophiles and the diastereoselectivity is not switchable. [9a] Herein, we report a Cu I -P,N-ferrocene-catalyzed 1,3-dipolar cycloaddition of nitroalkenes to an imino ester derived from glycine and our observation of a dramatic switch in exo/endo selectivity due to