Asymmetric dearomatization of indoles through a Michael/Friedel-Crafts-type cascade to construct polycyclic spiroindolines.

A highly efficient asymmetric dearomatization of indoles was realized through a cascade reaction between 2-isocyanoethylindole and alkylidene malonates catalyzed by a chiral N,N'-dioxide/Mg(II) catalyst. Fused polycyclic indolines containing three stereocenters were afforded in good yields with excellent diastereo- and enantioselectivities through a Michael/Friedel-Crafts/Mannich cascade. When 2-substituted 2-isocyanoethylindoles were used, spiroindoline derivatives were obtained through a Michael/Friedel-Crafts reaction.