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.

K2S2O8-Promoted Consecutive Tandem Cyclization/Oxidative Halogenation: Access to 3-Halo-Pyrazolo[1,5-a]pyrimidines

A one-pot methodology has been developed to synthesize 3-halo-pyrazolo[1,5-a]pyrimidine derivatives through the three-component reaction of amino pyrazoles, enaminones (or chalcone), and sodium halides. The use of easily accessible 1,3-biselectrophilic reagents like enaminones and chalcone offers a straightforward approach for the synthesis of 3-halo-pyrazolo[1,5-a]pyrimidines. The reaction proceeded through a cyclocondensation reaction between amino pyrazoles with enaminones/chalcone in the presence of K₂S₂O₈ followed by oxidative halogenations by NaX-K₂S₂O₈. Mild and environmentally benign reaction conditions, wide functional group tolerance, and scalability of the reaction are the attractive facet of this protocol. The combination of NaX-K₂S₂O₈ is also beneficial for the direct oxidative halogenations of pyrazolo[1,5-a]pyrimidines in water.

Lewis Acid-Catalyzed 1,4-Addition and Annulation of 4-Hydroxy-coumarins with o-Hydroxyphenyl Propargyl Amines: Entry to Regio-Selective Synthesis of Furano[3,2-c]coumarins and Pyrano[3,2-c]coumarins

A facile and regioselective Lewis acid-catalyzed cascade annulation of o-hydroxyphenyl propargyl amines with 4-hydroxycoumarin to afford furano[3,2-c]coumarin and pyrano[3,2-c]coumarin derivatives is reported. The reaction presumably proceeds by the conjugate addition of 4-hydroxycoumarin to the in situ-generated alkynyl o-quinone methide and is followed by intramolecular 5-exo-dig and 6-endo-dig annulation to form furano[3,2-c]coumarins and pyrano[3,2-c]coumarins, respectively. The prepared o-hydroxyl substituted pyrano[3,2-c]coumarins could be readily transformed into the corresponding coumarin-derived dioxabicycles by acid-mediated cyclization.

Visible-light-induced cascade reaction: a sustainable approach towards molecular complexity

Photoredox catalysis has demonstrated rapid evolution in the field of synthetic organic chemistry. On the other hand, the splendour of cascade reactions in providing complex molecular architectures renders them a cutting-edge research area. Therefore, the merging of photocatalysis with cascade synthesis brings out a synthetic paradigm with immense potential. The development of photocascade catalysis for a target molecule with a particular molecular skeleton and stereochemical framework presents certain challenges but provides a robust and environmentally benign synthetic alternative. This comprehensive review assembles all the accomplishments and highlights of visible-light-induced cascade reactions with literature coverage up to October 2022.

Domino Sonogashira coupling/metal carbene-involved annulation enabled by Pd/Cu relay catalysis: rapid assembly of indazole-containing biheteroaryls

An efficient and novel method has been developed for the synthesis of indazole-containing biheteroaryls via a domino Sonogashira coupling/azaenyne cycloisomerization/Barton–Kellogg reaction.

Copper-Catalyzed Cascade Annulation of o-Hydroxyphenyl Propargylamines with Pyrazolin-5-ones to Access Pyrano[2,3-c]pyrazoles

An efficient copper-catalyzed cascade annulation of o-hydroxyphenyl propargylamines and pyrazolin-5-ones is described. This methodology leads to the rapid assembly of a series of valuable pyrano[2,3-c]pyrazoles with good yields across a wide range of substrates in a simple fashion. This novel reaction involves the formation of alkynyl ortho-quinone methides, a 1,4-conjugate addition, and a subsequent 6-endo cyclization process. The mechanistic elucidation is well supported by control experiment and literature precedents.

Synthesis of Unsymmetrical Biheteroarenes via Dehydrogenative and Decarboxylative Coupling: a Decade Update

The design and development of robust and efficient methods for installing one heterocycle with another is endowed as a ubiquitous and powerful synthetic strategy to access complex organic biheterocycles in recent days due to their pervasive applications in medicinal as well as material chemistry. This perspective presents an overview on the recent findings and developments for the synthesis of unsymmetrical biheteroarenes via dehydrogenative and decarboxylative couplings with literature coverage mainly extending from 2011 to 2021. For simplification of the readers, the article has been subcategorized based on the catalysts used in the reactions.

Synthesis of naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via Rh(iii)-catalyzed C–H functionalization of 2-arylimidazo[1,2-a]pyridines with cyclic 2-diazo-1,3-diketones featuring with a ring opening and reannulation

An unprecedented synthesis of functionalized naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via rhodium-catalyzed cascade reactions of 2-arylimidazo[1,2-a]pyridine-3-carbaldehydes with cyclic α-diazo-1,3-diketones is presented.

Highly Regioselective, Acid-Catalyzed, Three-Component Cascade Reaction for the Synthesis of 2-aminopyridine-Decorated Imidazo[1,2- a]pyridine

A highly regioselective acid-catalyzed three-component reaction of 2-aminopyridine and 3-phenylpropiolaldehyde for the construction of imidazo[1,2- a]pyridine has been developed. This strategy provides a broad range of substrates and represents an efficient approach to give various 2-aminopyridine-decorated imidazo[1,2- a]pyridine in good yields.

Superparamagnetic nanoparticle-catalyzed coupling of 2-amino pyridines/pyrimidines with trans-chalcones

An aerobic coupling of 2-aminopyrimidines or 2-aminopyridines with trans-chalcones to afford aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines is reported. Reactions proceed in the presence of CuFe₂O₄ superparamagnetic nanoparticle catalyst, two equivalents of iodine, oxygen oxidant, and 1,4-dioxane solvent. The catalyst is superior to many common copper or iron complexes. Copper ferrite could be easily separated by magnetic decantation and reused up to 5 times without a major loss of activity. The method described here marks a rare example of using a simple, heterogeneous catalyst for synthesis of fused heterocycles. To our best knowledge, aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines were not previously synthesized using this protocol.

An aerobic coupling of 2-aminopyrimidines or 2-aminopyridines with trans-chalcones to afford aroylimidazo[1,2-a]pyrimidines and aroylimidazo[1,2-a]pyridines is reported.

3-Heterosubstituted Benzofurans from Hydroxyphenyl Propargyl Alcohols via ortho-Quinone Methide through a Metal-/Catalyst-Free Conjugate Addition/Oxy-Cyclization

A facile route to 3-sulfonylated and 3-(1-benzotriazolyl)-benzofurans is achieved from readily available o-hydroxyphenyl propargyl alcohols (o-HPPAs) and bench-top sodium sulfonylates and benzotriazoles with no assistance of any reagent or catalyst. Bifunctional o-quinone methides (o-QMs) were the putative reaction intermediates ensued from dehydration of o-HPPA. Our study revealed that the o-QM was so choosy in selection of the nucleophiles for the key Michael addition reaction.

Ruthenium-catalyzed tandem annulation/arylation for the synthesis of unsymmetrical bis(heteroaryl)methanes

A new Ru-catalyzed tandem furan annulation/arylation strategy has been developed to afford unsymmetrical bis(heteroaryl)methanes by a reaction between propargyl amines and indoles. A series of bis(heteroaryl)methanes containing furan and indole as well as indole and imidazopyridine moieties have been synthesized in high yields. The reaction possibly proceeds through furan annulation followed by nucleophilic addition of indole.