The bora-ene reaction of sulfur dioxide and prop-2-ene-1-boronic esters. New route to sulfoxides

A new one-pot synthesis of sulfoxides is presented. It involves the bora-ene reaction of sulfur dioxide and prop-2-ene-1-boronic esters, giving mixed anhydrides of sulfinic and boric acids. The latter react chemoselectively at the sulfur center with Grignard reagents in displacement reactions giving the corresponding prop-2-en-1-ylsulfoxides. Preliminary studies on the chirality transfer of enantiomerically enriched boronates to the sulfoxides are also presented.