Copper-Catalyzed Electrochemical Selective Bromination of 8-Aminoquinoline Amide Using NH₄Br as the Brominating Reagent

Abstract

A simple and mild protocol for copper-catalyzed bromination of quinoline at the C5 site of quinoline by anodic oxidation was developed, affording the desired remote C–H activation products with isolated yields of up to about 90%. The reaction proceeds with low-cost NH4Br and shows mild and green conditions (electricity as a green oxidant; NH3 and H2 as byproducts). At the same time, a gram-scale bromination reaction was also successfully fulfilled, showing its potential applicable value in organic synthesis. Moreover, the CV chart further demonstrated the proposed catalytic cycle.

Iodine-Catalyzed Synthesis of N,N′-Chelate Organoboron Aminoquinolate

“…13 5-Bromoquinolin-8-amine (1r). 27 EtOAc/petroleum = 1:10, R f = 0.45, 43.3 mg, 98% yield. 1 Sodium Tetra-p-tolylborate (2aa).…”

Recent Applications of Homogeneous Catalysis in Electrochemical Organic Synthesis

“…42 Xie and co-workers achieved the first example of Cu-catalyzed electrochemical B-H oxygenation reactions of ocarboranes by introducing an 8-aminoquinoline as a directing group at room temperature (Figure 4e). 43 The use of a chelating directing group for Cu-catalyzed electrochemical bromination reactions was reported by the Mei group, who used NH 4 Br as a bromine source (Figure 4f); 44 In 2021, the Sevov group reported ligand-free catalysis with a Cu salt, a process that tends to be challenging because of the potential for reductive deposition of Cu 0 at the cathode, which is avoided in Cu catalysis with ligands. Sevov et al carried out electrochemical homogeneous Chan-Lam coupling reactions between amines 5-1 and aryl boronic acids 5-2 with Cu(OAc) 2 as a catalyst and Fc + as an anodic mediator and obtained moderate to excellent yields of anilines 5-3 (Figure 5a).…”

Electrolyte‐Triggered C5‐Selective Trifluoromethylation and Halogenation of 8‐Aminoquinoline Derivatives

“…In 2019, Lei′s group [16] developed a direct electrochemical oxidative trifluoromethylation of arenes. Very recently, Fang's group [15] reported a copper‐catalyzed electrochemical bromination of 8‐aminoquinoline using NH 4 Br as brominating reagent. Inspired by the great achievements of these electrochemical and combined with our privious work, [17] we decided to carry out the research on trifluoromethylation and halogenation at C5 positions of 8‐aminoquinoline derivatives under constant‐current conditions.…”