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 (<i>E</i>)-3-(oxyethylidene)-2-oxoindolines with 1-alkyl-3-oxotetrahydro-1<i>H</i>-thiophen-1-ium salts as cyclic sulfur ylides was realized by using a chiral <i>N</i>,<i>N</i>′-dioxide/Mg­(OTf)<sub>2</sub> complex as catalyst. A range of sulfur-containing <i>syn</i>,<i>anti</i> 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.