Organocatalytic Direct Asymmetric Aldol Reactions of 3-Isothiocyanato Oxindoles to Ketones: Stereocontrolled Synthesis of Spirooxindoles Bearing Highly Congested Contiguous Tetrasubstituted Stereocenters

The first example of a direct catalytic asymmetric intermolecular aldol reaction of 3-isothiocyanato oxindoles to simple ketones with bifunctional thiourea-tertiary amine as catalyst is reported. This strategy provides a promising approach for the asymmetric synthesis of a range of enantioenriched spirocyclic oxindoles bearing two highly congested contiguous tetrasubstituted carbon stereocenters. Versatile transformations of the spirocyclic oxindole products into other structurally diverse spirocyclic oxindoles have also been demonstrated.