Recent Developments in Transition‐Metal‐Catalyzed Regioselective Functionalization of Imidazo[1, 2‐ a ]pyridine

Current Market Potential and Prospects of Copper-based Pyridine Derivatives: A Review

Nicotine, minodronic acid, nicotinamide (niacin), zolpidem, zolimidine, and other pyridine-based chemicals play vital roles in medicine and biology. Pyridinecontaining drugs are widely available on the market to treat a wide range of human ailments. As a result of these advances, pyridine research is continually expanding, and there are now higher expectations for how it may aid in the treatment of numerous ailments. This evaluation incorporates data acquired from sources, like PubMed, to provide a thorough summary of the approved drugs and bioactivity data for compounds containing pyridine. Most of the reactions discussed in this article will provide readers with a deeper understanding of various pyridine-related examples, which is necessary for the creation of copper catalysis-based synthetic processes that are more accessible, secure, environmentally friendly, and practical, and that also have higher accuracy and selectivity. This paper also discusses significant innovations in the multi-component copper-catalyzed synthesis of N-heterocycles (pyridine), with the aim of developing precise, cost-effective, and environmentally friendly oxygenation and oxidation synthetic methods for the future synthesis of additional novel pyridine base analogs. Therefore, the review article will serve as a novel platform for researchers investigating copperbased pyridine compounds.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

Catalyst-Controlled Regiodivergent Oxidative Annulation of 2-Arylimidazo[1,2-a]pyridines with Cinnamaldehyde Derivatives for Construction of Fused N-Heterocyclic Frameworks

Catalyst-dependent regioselective oxidative annulation of 2-arylimidazo[1,2-a]pyridines with cinnamaldehyde derivatives to construct fused N-heterocyclic frameworks has been described. The annulation reaction afforded 5-arylnaphtho[1',2':4,5]imidazo[1,2-a]pyridine-6-carbaldehydes in the presence of [RhCp*Cl2]2 as catalyst while 1,7-diarylimidazo[5,1,2-cd]indolizine-6-carbaldehydes were obtained using Pd(OAc)2 as catalyst. The reaction produced annulated products in good yields and exhibited broad substrate scope and excellent functional group tolerance. The method provides two different isomeric annulated products bearing an aldehyde functionality which can be elaborated into an array of functionalities leading to valuable compounds.

Unlocking Regiodivergence in PdII- and RhIII-Mediated Site-Selective C-H Bond Alkynylation of Imidazopyridines

An efficient Pd^II- and Rh^III-controlled site-selective C-H bond alkynylation of imidazopyridines using (bromoethynyl)triisopropylsilane is disclosed. The divergent methodology allows straightforward access to a wide range of products alkynylated at the C3 and ortho positions. This strategy is suggestive of a practical platform that can be suitable for late-stage diversification and may assist in the design of more selective and complementary catalytic systems.

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes

Alkynyl selenides have attracted considerable research interest recently, owing to their applications in the biological and pharmaceutical fields. The Cu-catalyzed tandem reaction for the synthesis of novel alkynyl imidazopyridinyl selenides is presented. A one-pot synthesis route afforded alkynyl imidazopyridinyl selenides in moderate to good yields. This was achieved by a two-step reaction between terminal alkynes and diimidazopyridinyl diselenides, generated from imidazo[1,2-a]pyridines and Se powder, using 10 mol % of CuI and 1,10-phenanthroline as the catalytic system under aerobic conditions. The C(sp²)–Se and C(sp)–Se bond-formation reaction can be performed in one-pot by using inexpensive and easy to handle Se powder as the Se source. The reaction proceeded with terminal alkynes having various substitutions, such as aryl, vinyl, and alkyl groups. The obtained alkynyl imidazopyridinyl selenide was found to undergo nucleophilic substitution reaction on Se atom using organolithium reagents and 1,3-dipolar azide–alkyne cycloaddition based on the alkyne moiety.

Reaction of imidazo[1,2-a]pyridines with coumarin-3-carboxylic acids: a domino Michael addition/decarboxylation/oxidation/annulation

A palladium-catalyzed decarboxylative domino reaction of imidazo[1,2-a]pyridines and coumarin-3-carboxylic acids has been developed, which provides access to dibenzoisochromenoimidazo[1,2-a]pyridin-6-ones possessing six fused rings.

Recent Progress in Metal-Free Direct Synthesis of Imidazo[1,2-a]pyridines

This Mini-Review highlights the most effective protocols for metal-free direct synthesis of imidazo[1,2-a]pyridines, crucial target products and key intermediates, developed in the past decade. The emphases is given on the ecological impact of the methods and on the mechanistic aspects as well. The procedures efficiently applied in the preparation of important drugs and promising drug candidates are also underlined.

Ortho C-H Functionalization of 2-Arylimidazo[1,2-a]pyridines

C-H activation and functionalization is quite promising in recent days as the strategy offers a go-to general method for different bond formations and hence grants synthetic versatility. At the same time, imidazopyridine, a fused bicycle of imidazole moiety with pyridine ring, has a profound impact due to its ubiquitous and prodigious application in medicinal as well as material chemistry. The presence of N-1 atom in 2-arylImidazo[1,2-a]pyridine facilitates the coordination with metal catalysts leading to the formation of ortho-substituted products. This review summarizes all the articles on ortho C-H functionalization of 2-arylImidazo[1,2-a]pyridines published till August 2021.

Solvent-Switched Manganese(I)-Catalyzed Regiodivergent Distal vs Proximal C-H Alkylation of Imidazopyridine with Maleimide

A sustainable Mn(I)-catalyzed exclusive solvent-dependent functionalization of imidazopyridine with maleimide via an electrophilic metalation at the distal (in 2,2,2-trifluoroethanol (TFE)) and chelation assisted at the proximal (in tetrahydrofuran (THF)) has been developed. The strategy was successfully applied to the drug Zolimidine and a broad range of substrates, thereby reflecting the method's versatility.