Chiral Hypervalent Bromine(III) (Bromonium Salt): Hydrogen- and Halogen-Bonding Bifunctional Asymmetric Catalysis by Diaryl‑λ3‑bromanes

Bromonium salts, which are hypervalent bromine reagents, have been explored as being strong electrophiles owing to their extremely high nucleofugalities. Only one example of their catalytic application has been reported by our group; however, their chiral versions have not yet been researched. Halogen-bonding (XB) has been widely applied in chemistry; however, its successful application to highly enantioselective Lewis acid catalysis has not yet been achieved. Herein, we report the design and development of chiral cyclic diarylbromonium salts. These catalysts enabled a highly enantioselective Lewis acid XB catalysis, giving products with up to 96% ee.