Cu(II)/DM-Segphos catalyzed asymmetric 1,3-dipolar cycloaddition of benzoisothiazole-2,2-dioxide-3-ylidenes and azomethine ylides

Cu(OTf)2/DM-Segphos catalyzed asymmetric 1,3-dipolar cycloaddition between benzoisothiazole-2,2-dioxide-3-ylidenes and azomethine ylides was studied. The spiropyrrolidinyl-benzoisothiazolines were obtained in high yields with up to >99 : 1 dr and 99% ee. The enantioselective cycloaddition could be explained by the coordination of the imino esters 2 and chiral ligand DM-Segphos to the metallic center. The exo-selective cycloaddition course was attributed to the steric repulsion between the dipolarophiles and the 3,5-dimethylphenylphosphine group of the ligand.