Organocatalytic asymmetric [3+2] cycloaddition of N-2,2,2-trifluoroethylisatin ketimines with 3-alkenyl-5-arylfuran-2(3H)-ones: Efficient synthesis of spiro[pyrrolidin-3,2′-oxindoles bearing four consecutive stereocenters with two vicinal spiroquaternary chiral centers.
