Cu-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of Azomethine Ylides with beta-Phenylsulfonyl Enones. Ligand Controlled Diastereoselectivity Reversal

A catalytic asymmetric procedure for the 1,3-dipolar cycloaddition of (E)-beta-phenylsulfonyl enones with azomethine ylides to provide highly functionalized pyrrolidine derivatives is described. In the presence of chiral Cu-I-Segphos catalysts the aducts were obtained with high regio-, diastereo-, and enantioselectivity. Interestingly, a switch from endo to exo selectivity was observed when Segphos or DTBM-Segphos ligand was used.