Electrochemical Generation of Hypervalent Bromine(III) Compounds

In sharp contrast to hypervalent iodine(III) compounds, the isoelectronic bromine(III) counterparts have been little studied to date. This knowledge gap is mainly attributed to the difficult‐to‐control reactivity of λ3‐bromanes as well as to their challenging preparation from the highly toxic and corrosive BrF3 precursor. In this context, we present a straightforward and scalable approach to chelation‐stabilized λ3‐bromanes by anodic oxidation of parent aryl bromides possessing two coordinating hexafluoro‐2‐hydroxypropanyl substituents. A series of para‐substituted λ3‐bromanes with remarkably high redox potentials spanning a range from 1.86 V to 2.60 V vs. Ag/AgNO3 was synthesized by the electrochemical method. We demonstrate that the intrinsic reactivity of the bench‐stable bromine(III) species can be unlocked by addition of a Lewis or a Brønsted acid. The synthetic utility of the λ3‐bromane activation is exemplified by oxidative C−C, C−N, and C−O bond forming reactions. A straightforward electrochemical synthesis of chelation‐stabilized hypervalent bromine(III) compounds is presented. The electrolysis proceeds at room temperature in an undivided cell under galvanostatic conditions, giving λ3‐bromanes in good yields on the gram scale from bromoarenes. The reactivity of λ3‐bromanes can be enhanced by Lewis or Brønsted acid additives as demonstrated in λ3‐bromane‐mediated oxidative biaryl formation.