A Co(ii)-catalyzed asymmetric ring opening reaction of spiro-epoxyoxindoles with allylboron†
Stereoconvergent reactions of epoxides are challenging and very limited. Herein, we report the first stereoconvergent ring opening allylation of epoxides, which was catalysed by a Co(II)/bisoxazoline catalyst, to realize the reaction between spiroepoxyoxindoles and potassium allyltrifluoroborate. This catalytic system can tolerate a wide range of spiroepoxyoxindoles. The desired chiral oxindoles bearing quaternary stereocenters could be prepared with yields of 64–90% and enantioselectivities of 57–78%. A gram-scale reaction showed the practical applicability of this enantioselective catalysis. Furthermore, preliminary mechanistic studies indicate that this reaction proceeds via a sequential epoxide-ring-opening and enantioselective addition process.