Electrochemical Bromination of Glycals

Abstract

Herein, the convenient one-step electrochemical bromination of glycals using Bu4NBr as the brominating source under metal-catalyst-free and oxidant-free reaction conditions was described. A series of 2-bromoglycals bearing different electron-withdrawing or electron-donating protective groups were successfully synthesized in moderate to excellent yields. The coupling of tri-O-benzyl-2-bromogalactal with phenylacetylene, potassium phenyltrifluoroborate, or a 6-OH acceptor was achieved to afford 2C-branched carbohydrates and disaccharides via Sonogashira coupling, Suzuki coupling, and Ferrier rearrangement reactions with high efficiency. The radical trapping and cyclic voltammetry experiments indicated that bromine radicals may be involved in the reaction process.

Electrochemical assembly of isoxazoles via a four-component domino reaction

“…Interestingly, LiBr as an electrolyte exhibited better electron transfer efficiency than n -Bu 4 NPF 6 but was, however, slightly inferior to n -Bu 4 NBr, suggesting the potential significance of the bromine anion in the synthesis (entry 3). 13 The introduction of acid into the reaction system proved to be advantageous for the reaction efficiency, with trifluoroacetic acid (TFA) being optimal (entry 4). 14 Control experiments confirmed the indispensable role of electricity while also suggesting the dual functionality of TBN as both the substrate and oxidation agent (entries 5–6).…”

“…Based on the aforementioned findings and existing reports, 16 we propose a plausible reaction mechanism, which is depicted in Scheme 2 . Initially, bromine anions from the electrolyte undergo oxidation at the anode, 13 leading to the formation of bromine radical I. Simultaneously, under thermal conditions, TBN undergoes homolysis, generating radicals II and III.…”

Metal-Free Synthesis of N-Heterocycles via Intramolecular Electrochemical C-H Aminations

“…Organic electrosynthesis utilizes electricity as the driving force to activate substrates of interest, thus offering a sustainable way to obtain reactive intermediates for organic synthesis ( Li et al, 2019 ; Meyer et al, 2020 ; Luo et al, 2021 ; Novaes et al, 2021 ; Chen et al, 2022 ; Qian et al, 2022 ; Tan et al, 2022 ; Wang and Xu, 2022 ). Recently, organic electrosynthesis has undergone considerable renaissance, and provided unique reactivities that are not accessible with traditional synthetic methodologies.…”