Catalytic Asymmetric [8+3] Annulation Reactions of Tropones or Azaheptafulvenes with meso-Aziridines.

Highly enantioselective [8+3] high-order cycloaddition reactions of tropones or azaheptafulvenes with meso-aziridines were achieved by a desymmetrization/annulation process in the presence of chiral N,N'-dioxide/Mg(OTf)2 complex. The corresponding tetrahydrocyclohepta[b][1,4]oxazines and tetrahydro-1H-cyclohepta- [b]-pyrazines were obtained in good yields (66-98 %) with excellent diastereo- and enantioselectivities (>19:1 d.r., 90-96 % ee). A possible transition state model was proposed to elucidate the origin of chiral induction based on the control experiments and X-ray crystal structure of the catalyst.