Electrochemical Bromofunctionalization of Alkenes and Alkynes—To Sustainability and Beyond

Abstract

The electrochemical generation of highly reactive and hazardous bromine under controlled conditions as well as the reduction of surplus oxidizers and reagent waste has placed electrochemical synthesis in a highlighted position. In particular, the electrochemical dibromination and bromofunctionalization of alkenes and alkynes have received significant attention, as the forming of synthetically important derivatives can be generated from bench-stable and safe bromide sources under “green” conditions. Readily available and non-corrosive bromide salts have been utilized with a dual role as both a reagent and supporting electrolyte. However, this trend seems to change with the preparation of organobromine species. In this review, the electrochemical dibromination and bromofunctionalization of alkenes and alkynes was addressed in terms of their bromine sources and sustainability.

A tutorial on asymmetric electrocatalysis

“…67 For example, in electrochemical syntheses, halide salts can be oxidized at the anode to provide reactive halogen species, with the sole by-product being hydrogen generated from proton reduction at the cathode, whereas the equivalent chemical reaction would require the use of an electrophilic halogen source. 68 Indeed, as discussed in this section, the earliest examples of asymmetric electrocatalysis leveraged an electric current to provide the redox equivalents in lieu of stoichiometric chemical oxidants and reductants to improve the greenness, safety, and scalability of well-established traditional asymmetric catalysis.…”

Multigram Electrochemical Hofmann Rearrangement Using a Spinning Three-Dimensional Anode

“…Graphite is a cost-efficient carbon-based material, which is able to generate active bromine species from bromide salts. 17 Interestingly, although graphite performed poorly compared to Pt under analogous conditions (entry 3 vs 4), decreasing the amount of MeOH to 5 equiv significantly increased the reaction conversion (>99%), although an unsatisfactory selectivity toward carbamate 2a (86%) was observed (entry 5). Other inorganic bromide salts, namely, KBr and LiBr, did not improve the results with respect to NaBr (entries 6 and 7).…”

“…As platinum is an undesired material for large-scale experimentation due to its cost, graphite was tested next as the anode material. Graphite is a cost-efficient carbon-based material, which is able to generate active bromine species from bromide salts . Interestingly, although graphite performed poorly compared to Pt under analogous conditions (entry 3 vs 4), decreasing the amount of MeOH to 5 equiv significantly increased the reaction conversion (>99%), although an unsatisfactory selectivity toward carbamate 2a (86%) was observed (entry 5).…”

Electrochemical four-component aminochlorination tuned by benzimidazoles

“…Synthetic electrochemistry provides a general and distinct platform for conventional redox transformations, 4 and explosive progress has been witnessed in the difunctionalization of alkenes. 5 However, to the best of our knowledge, the electrochemical intermolecular amino-chlorination 6 of alkenes still remains uncultivated. Three main challenging issues have yet to be solved (Scheme 1c): (a) undesirable dichlorination 7 would lead to inferior chemoselectivity; (b) anodically generated chlorine radical species would cause poor stereoselectivity in the transformation; (c) conventional amination reagents might be incompatible with the reaction, as a highly nucleophilic amination reagent would result in direct oxidation of the reagent or low nucleophilic ones could show diminished reactivity.…”