The chemistry of hypervalent halogen species has experienced remarkable advancement in the recent decades [1]. However, in comparison to the well-explored hypervalent iodine(III) compounds, little research has been done on the isoelectronic bromine(III) counterparts [2]. This is mainly due to the difficult-to-control reactivity of λ³-bromanes as well as to the challenges associated with the conventional protocol for their preparation from the highly toxic and corrosive precursor BrF₃ [3]. In this context, we present a straightforward and scalable approach to λ³-bromanes by anodic oxidation of parent aryl bromides. 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 bench-stable bromine(III) species can be activated by addition of a Lewis or a Brønsted acid and used for various synthetic applications [4].

The developed electrochemical approach to λ³-bromanes offers considerable advantages compared to previously established methods since stoichiometric reagents are replaced by electric current and the use of hazardous precursors is omitted. Therefore, our approach may open the door to the development of unprecedented synthetic transformations that would benefit from the unique properties of hypervalent bromine(III) species. Mechanistic studies on formation and activation of the bromanes are underway [5].

References:
1. Yoshimura, A.; Zhdankin, V. V., Chem Rev 2016, 116, 3328-435.
2. Miyamoto, K., Chemistry of Hypervalent Bromine. In PATAI'S Chemistry of Functional Groups 2018, pp 1-25.
3. Farooq, U.; Shah, A. A.; Wirth, T., Angew. Chem. Int. Ed. 2009, 48, 1018-1020.
4. Sokolovs, I.; Mohebbati, N.; Francke, R.; Suna, E., Angew. Chem. Int. Ed. 2021, 60, 15832-15837.
5. Mohebbati, N.; Sokolovs, I.; Woitke, P.; Leito, I.; Roemelt, M.; Suna, E.; Francke, R.; 2022, manuscript in preparation.