Copper(I) Iodide/Boron Trifluoride Etherate-Cocatalyzed Aerobic Dehydrogenative Reactions Applied in the Synthesis of Substituted Heteroaromatic Imidazo[1,2-a]pyridines

Regioselective synthesis and molecular docking studies of functionalized imidazo [1,2-a]pyridine derivatives through MCRs

A efficient protocol has been developed for the synthesis of regioselective imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidine derivatives through cascade reaction between 2-aminopyridine, arylelglyoxal, and 4-hydroxypyran via three-component reaction to prepare targeted compounds with good to excellent yields. The advantages of this transformation are a catalyst-free reaction, green solvent, operationally simple, scalable, and eco-friendly. The product collects with simple filtration which avoided tedious and expensive purification techniques. In addition, computational studies like molecular docking were conducted to provide the theoretical possibilities of binding these types of synthesized compounds to the VEGFR2 receptors as potential key inhibitors of tumor cell growth and angiogenesis.

Synthetic Imidazopyridine-Based Derivatives as Potential Inhibitors against Multi-Drug Resistant Bacterial Infections: A Review

Fused pyridines are reported to display various pharmacological activities, such as antipyretic, analgesic, antiprotozoal, antibacterial, antitumor, antifungal, anti-inflammatory, and antiapoptotic. They are widely used in the field of medicinal chemistry. Imidazopyridines (IZPs) are crucial classes of fused heterocycles that are expansively reported on in the literature. Evidence suggests that IZPs, as fused scaffolds, possess more diverse profiles than individual imidazole and pyridine moieties. Bacterial infections and antibacterial resistance are ever-growing risks in the 21st century. Only one IZP, i.e., rifaximin, is available on the market as an antibiotic. In this review, the authors highlight strategies for preparing other IZPs. A particular focus is on the antibacterial profile and structure-activity relationship (SAR) of various synthesized IZP derivatives. This research provides a foundation for the tuning of available compounds to create novel, potent antibacterial agents with fewer side effects.

Diversity-oriented synthesis of imidazo[1,2-a][1,3,5]triazine derivatives from 2-amine-[1,3,5]triazines with ketones

An I₂-mediated annulation of 2-amino[1,3,5]triazines and ketones for the synthesis of imidazo[1,2-a][1,3,5]triazines is presented. Electron rich, or electron poor acetophenone and heterocycle ketones, as well as propiophenone, are functionalized with 2-amino-[1,3,5]triazines. Another class of imidazo[1,2-a][1,3,5]triazines tethered with an additional 1,2-dicarbonyl motif through the combination of annulation and C-H functionalization were obtained instead by changing the reaction conditions. The new methods are practically straightforward and applicable on a gram scale.

Iodine Promoted Efficient Synthesis of 2-Arylimidazo[1,2-a]pyridines in Aqueous Media: A Comparative Study between Micellar Catalysis and an "On-Water" Platform

In a new and environmentally sustainable approach, a series of 2-arylimidazo[1,2-a]pyridine derivatives were synthesized in aqueous media in the presence of iodine as a catalyst. The reaction proceeded by condensation of various aryl methyl ketones with 2-aminopyridines to afford 2-arylimidazo[1,2-a]pyridines in good overall yields. Although several of the reactions were efficiently performed "on water", the addition of a surfactant, namely, sodium dodecyl sulphate , was found effective in terms of substrate scope and yield enhancement. Both methods were successfully used for the gram-scale synthesis of a marketed drug, zolimidine. The simple experimental setup, water as "green" media, and inexpensive catalyst are some of the merits of this protocol.

Lewis Acid-Catalyzed Intermolecular Annulation: Three-Component Reaction toward Imidazo[1,2-a]pyridine Thiones

A Lewis acid-catalyzed three-component annulation reaction of 2-aminopyridines and ynals with elemental sulfur was established. A series of imidazo[1,2-a]pyridine thiones was obtained in moderate to excellent yields. The merits of this transformation include easily available starting materials, multiple C-heteroatom bond formation in one pot, good functional group tolerance, elemental sulfur as S source, operational simplicity, etc.

Chemodivergent synthesis of N-(pyridin-2-yl)amides and 3-bromoimidazo[1,2-a]pyridines from α-bromoketones and 2-aminopyridines

N-(Pyridin-2-yl)amides and 3-bromoimidazo[1,2-a]pyridines were synthesized respectively from α-bromoketones and 2-aminopyridine under different reaction conditions.

Copper-catalyzed oxidative multicomponent reaction: synthesis of imidazo fused heterocycles with molecular oxygen

An oxidative cascade that involves multicomponent reaction comprising a terminal alkyne, 2-amino N-heterocycle, benzyl or allylic bromide with molecular oxygen, delivering densely functionalized imidazo fused heterocycles, is described. This reaction features a cheap catalyst, a green oxidant, and readily available starting materials, which make the overall synthesis applicable in the quick access to relevant pharmaceutical molecules with imidazole derived heterocycles.

Metal- and base-free synthesis of imidazo[1,2-a]pyridines through elemental sulfur-initiated oxidative annulation of 2-aminopyridines and aldehydes

An elemental sulfur-based metal- and base-free system enables oxidative imidazo[1,2-a]pyridine annulations.

Oxidative organophotoredox catalysis: a regioselective synthesis of 2-nitro substituted imidazopyridines and 3-substituted indoles, initiated by visible light

Intramolecular C–N heterocyclization and C–C bond formation under visible light irradiation at room temperature was accomplished with a metal-free photoredox catalyst.

Fe–SBA-15 catalyzed synthesis of 2-alkoxyimidazo[1,2-a]pyridines and screening of their in silico selectivity and binding affinity to biological targets

Regioselective synthesis of 2-alkoxyimidazopyridines by Fe-SBA-15 and screening of their in silico binding affinity to biological targets.

Nano-NiFe2O4 catalyzed microwave assisted one-pot regioselective synthesis of novel 2-alkoxyimidazo[1,2-a]pyridines under aerobic conditions

Here, we have demonstrated regioselective synthesis of novel 2-alkoxy-3-arylimidazo[1,2-a]pyridines using nano-NiFe₂O₄ as reusable catalyst via one-pot sequential aza-Michael addition, Fe-promoted ligand transfer and C–H imination reactions.

Recent Trends in Copper-Catalyzed C-H Amination Routes to Biologically Important Nitrogen Scaffolds

Nitrogen-containing heterocycles have found remarkable applications in natural product research, material sciences, and pharmaceuticals. Although the synthesis of this interesting class of compounds attracted the interest of generations of organic chemists, simple and straightforward assembly methods based on transition-metal catalysis have regularly been elusive. The recent advancements in the development of C-H functionalization have helped in accomplishing the synthesis of a variety of complex heterocycles from simple precursors. This Focus Review summarizes the recent advances in one particular field: the copper-catalyzed C-N bond formation reactions via C-H bond functionalization to furnish a comprehensive range of nitrogen heterocycles. Applicability and synthetic feasibility of a particular reaction represent major requirements for the inclusion in this review.

Copper-catalyzed aerobic oxidative coupling: From ketone and diamine to pyrazine

Copper-catalyzed aerobic oxidative C-H/N-H coupling between simple ketones and diamines was developed toward the synthesis of a variety of pyrazines. Various substituted ketones were compatible for this transformation. Preliminary mechanistic investigations indicated that radical species were involved. X-ray absorption fine structure experiments elucidated that the Cu(II) species 5 coordinated by two N atoms at a distance of 2.04 Å and two O atoms at a shorter distance of 1.98 Å was a reactive one for this aerobic oxidative coupling reaction. Density functional theory calculations suggested that the intramolecular coupling of cationic radicals was favorable in this transformation.

Microwave-assisted synthesis of novel 2,3-disubstituted imidazo[1,2-a]pyridines via one-pot three component reactions

An expeditious one-pot, metal-free, three-component reaction of arylglyoxals, cyclic 1,3-dicarbonyls and 2-aminopyridines in the presence of molecular iodine under microwave irradiation is reported.

Copper-mediated three-component synthesis of 3-cyanoimidazo[1,2-a]pyridines

A copper-mediated three-component approach towards the synthesis of 3-cyanoimidazo[1,2-a]pyridines from 2-aminopyridines, acetophenones and benzyl cyanide was developed. This cascade reaction proceeds through a copper-mediated oxidative release of cyanide from benzyl cyanide, a copper-mediated Ortoleva–King reaction, and a copper-catalyzed cyanation.

A copper-catalyzed multi-component reaction accessing fused imidazo-heterocycles via C–H functionalization

An efficient synthesis of fused imidazo-heterocycles is described using Cu(OTf)₂ in [bmim]BF₄ by the multi-component reaction of pyridin-2(1H)-one or thiazol/benzo[d]thiazol-2(3H)-ones with O-tosylhydroxyl amine and acetophenones under microwave irradiation.

One-pot, three component tandem reaction of 2-aminopyridines, acetophenones and aldehydes: synthesis of 3-aroylimidazo[1,2-a]pyridines

A facile synthesis of 3-aroylimidazo[1,2-a]pyridine derivatives has been achieved via a copper(ii) chloride catalyzed one-pot, three-component tandem reaction of acetophenones, arylaldehydes and 2-aminopyridines.