Electrochemical Oxidative C3 Acyloxylation of Imidazo[1,2-a]pyridines with Hydrogen Evolution

Abstract

The C3-functionalized imidazo­[1,2-a]­pyridines are versatile nitrogen-fused heterocycles; however, the methods for the C3 acyloxylation of imidazo­[1,2-a]­pyridines have never been reported. Herein we demonstrate the electrochemical oxidative C3 acyloxylation of imidazo­[1,2-a]­pyridines for the first time. Notably, by using electricity, the electrochemical oxidative C3 acyloxylation of imidazo­[1,2-a]­pyridines was carried out under mild conditions. Moreover, in addition to aromatic carboxylic acids, alkyl carboxylic acids were also competent substrates.

Electrochemical Decarboxylative Coupling of N‐Substituted Glycines under Air: Access to C3‐Aminomethylated Imidazo[1,2‐a]pyridines

“…[3] Apart from transition metals, light, or oxidants involved approaches, electrochemistry proved to be a green and practical alternative approach to expand the chemical space of imidazo[1,2‐ a ]pyridine derivative by the process of losing or gaining electrons on the surface of electrodes [3d,f] . In the manner of electrochemical oxidation, except for the self‐coupling examples, [4] a variety of reagents including thiols, [5] diselenides, [6] diaryl amine, [7] imidazoles, [8] trialkyl phosphite, [9] sodium halides, [10] thiocyanates, [11] carboxylic acids, [12] and aryl sulfinates [13] have been successfully applied to the oxidative cross‐coupling of imidazo[1,2‐ a ]pyridines at the C3 position. However, to the best of our knowledge, no electrochemical decarboxylation coupling examples were reported.…”

“…However, to the best of our knowledge, no electrochemical decarboxylation coupling examples were reported. Although carboxylic acids have been used in the electrochemical coupling reaction with 2‐aryl imidazo[1,2‐ a ]pyridines, they only offered the direct dehydrogenative cross‐coupling products (Scheme 1a) [12] . Consequently, it is still worthy of turning attention to amino acids for the decarboxylative coupling with 2‐aryl imidazo[1,2‐ a ]pyridines.…”

Catalyst- and oxidant-free electrooxidative site-selective [3/4 + 2] annulation to fused polycyclic heteroaromatics

“…2-Phenylimidazo[1,2-a]pyridine 1 transformed into the stable radical cation intermediate 1-1 by anode oxidation firstly. 8,[11][12][13][14][15][16][17] A corresponding radical cation intermediate 3-1 was formed from the radical addition of intermediate 1-1 with alkyne 2.…”

“…10 In the past years, some interesting functionalizations of the imidazo[1,2- a ]pyridine moiety at the 3-position of the imidazole moiety have been reported, including amination, 11 phosphorylation, 12 cyanidation, 13 thiomethylation, 14 thiocyanation, 15 sulfonylation 16 and acyloxylation. 17 With our continued interest in the electrochemical generation and utilization of active radical intermediates, some electrochemical coupling, cyclization or migration methods to construct new C–C 18 and C–hetero 19 bonds have been previously reported by us.…”

Copper-catalyzed three-component reaction to synthesize polysubstituted imidazo[1,2-a]pyridines

“…In the past few years, reactions utilizing Cu, 12 Pd, 13 Mn, 14 TEMPO-mediated, 15 I 2 (ref. 16 ) and a few other catalysts 17 have provided attractive and valuable routes for the construction of imidazo[1,2- a ]pyridines. However, most reactions can only produce monosubstituted imidazo[1,2- a ]pyridines or halogenated intermediates ( Scheme 1a ) 18 which can undergo one more steps of coupling reaction leading to polysubstituted products.…”