Ligand-controlled switch in diastereoselectivities: catalytic asymmetric construction of spirocyclic pyrrolidine-azetidine/oxe(thie)tane derivatives.

An efficient catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides with four-membered ring-containing exocyclic alkenes has been developed, and either the exo or endo spirocyclic pyrrolidine-azetidine/oxe(thie)tane derivatives were diastereodivergently generated by employing Cu(i)/tBu-Phosferrox and a Cu(i)/N,O-ligand complex, respectively. Notably, various heteroatom-containing (N, O, S) exocyclic alkenes were found to be well-tolerated in this transformation.