Catalytic Asymmetric Ring-Opening/Cyclopropanation of Cyclic Sulfur Ylides: Construction of Sulfur-Containing Spirocyclopropyloxindoles with Three Vicinal Stereocenters.

A highly efficient asymmetric ring-opening/cyclopropanation reaction of ( E)-3-(oxyethylidene)-2-oxoindolines with 1-alkyl-3-oxotetrahydro-1 H-thiophen-1-ium salts as cyclic sulfur ylides was realized by using a chiral N, N'-dioxide/Mg(OTf)2 complex as catalyst. A range of sulfur-containing syn, anti spirocyclopropyloxindoles with three contiguous stereocenters were obtained in excellent yields with excellent dr and good ee values under mild reaction conditions. The origin of stereoselectivity was discussed.