Electrochemical Generation of Hypervalent Bromine(III) Compounds

Abstract

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.

Metal-free homo-/cross-anion–cation coupling of cyclic diaryl λ3-bromanes

“…17 Francke and Suna et al realized the electrochemical generation of chelationstabilized λ 3 -bromanes. 18 In addition to these mono-aryl bonded species, Wencel-Delord and co-workers disclosed a general, safe, and high-yielding strategy to access cyclic diaryl λ 3 -bromanes by using tBuONO as the oxidant. 19 They also achieved the arylation of cyclic diaryl λ 3 -bromanes with carboxylic acids and anilines, involving proton transfer from the substrate to the product (Scheme 1a).…”