Zn-Catalyzed Diastereo- and Enantioselective Cascade Reaction of 3-Isothiocyanato Oxindoles and 3-Nitroindoles: Stereocontrolled Syntheses of Polycyclic Spirooxindoles

A catalytic asymmetric Michael/cyclization cascade reaction of 3-isothiocyanato oxindoles and 3-nitroindoles has been disclosed with a chiral Zn(OTf)2/diphenylamine-linked bis(oxazoline) complex as the catalyst. A range of enantioenriched polycyclic spirooxindole derivatives containing three contiguous stereocenters were efficiently constructed in quantitative yields with excellent diastereo- and enantioselectivities. Importantly, the metal catalytic strategy in this work is significantly superior to the previous organocatalytic method in the diastereo- and enantioselectivities for almost all of the examined cases.