Diastereo- and Enantioselective Dearomative [3+2] Cycloaddition Reaction of 2-Nitrobenzofurans with 3-Isothiocyanato Oxindoles

Enantioselective dearomative [3 + 2] cycloaddition reaction of 2-nitrobenzofurans with 3-isothiocyanato oxindoles was developed. The reaction employs a chiral bis(oxazoline)/Zn(OTf)(2) catalyst, allowing a practical, straightforward access to structurally diverse spirooxindoles containing a 2,3-dihydrobenzofuran motif and three contiguous stereo-centers with excellent diastereo- and enantioselectivities. The synthetic potentials of the method have been demonstrated by the scale-up experiment and transformations of the products. The preliminary mechanism was investigated with experimental observations, nonlinear effects studies, and MS experiments.