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 lambda(3)-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 lambda(3)-bromanes by anodic oxidation of parent aryl bromides possessing two coordinating hexafluoro-2-hydroxypropanyl substituents. A series of para-substituted lambda(3)-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 Bronsted acid. The synthetic utility of the lambda(3)-bromane activation is exemplified by oxidative C-C, C-N, and C-O bond forming reactions.