Cyclopropanation of Propargyl Sulfonium Salts: Highly Diastereoselective Synthesis of Alkynylcyclopropanes

The first propargyl sulfur ylides involving a cyclopropanation
reaction between propargyl sulfonium salts and acrylonitrile derivatives
is presented. Propargyl sulfonium salts act as unusual alkyne-group-delivering
reagents in this transformation. Various alkynylcyclopropanes bearing
three contiguous stereocenters were constructed in moderate to high
yields with excellent diastereoselectivity under mild reaction conditions.