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-1H-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.