Cooperative Lewis acid-onium salt catalysis as tool for the desymmetrization of meso-epoxides.

Epoxide desymmetrizations by bromide are very rare despite the large synthetic potential of chiral bromohydrins. Herein we present a new concept for epoxide desymmetrizations in which a bifunctional Lewis acid/ammonium salt catalyst allows for efficient enantioselective epoxide ring openings by Br-. With acetylbromide as a Br- source bromohydrin esters are formed.