Catalytic enantioselective synthesis of chiral sulfonium ylides with S-stereogenic center

A sulfur stereogenic center is found in naturally occurring compounds and constitutes an important design element for pharmaceuticals and chiral auxiliaries. In view of the broad applications of S-stereogenic compounds, many methods were developed to enantioselectively construct the sulfur stereocenters. By contrast, the synthesis and isolation of S-stereogenic ylides was elusive although sulfonium ylides are important synthetic building blocks and such species have been proposed in the Doyle-Kirmse reaction. Using judicious substrate design, we have successfully developed the first catalytic enantioselective synthesis of sulfonium ylides with a chiral sulfur center. They are constructed from a broad array of sulfides in high yields (up to 98%) and enantioselectivities (up to 99%) through copper-catalyzed intramolecular carbene transfer reaction. The obtained ylides could be converted into alkylidenecyclopropanes with efficient sulfur-to-carbon chirality transfer.