A decade of advances in the reaction of nitrogen sources and alkynes for the synthesis of triazoles

Copper Dispersed Covalent Organic Framework for Azide-Alkyne Cycloaddition and Fast Synthesis of Rufinamide in Water

A crystalline porous bipyridine-based Bpy-COF with a high BET surface area (1864 m2 g-1) and uniform mesopore (4.0 nm) is successfully synthesized from 1,3,5-tris-(4'-formyl-biphenyl-4-yl)triazine and 5,5'-diamino-2,2'-bipyridine via a solvothermal method. After Cu(I)-loading, the resultant Cu(I)-Bpy-COF remained the ordered porous structure with evenly distributed Cu(I) ions at a single-atom level. Using Cu(I)-Bpy-COF as a heterogeneous catalyst, high conversions for cycloaddition reactions are achieved within a short time (40 min) at 25 °C in water medium. Moreover, Cu(I)-Bpy-COF proves to be applicable for aromatic and aliphatic azides and alkynes bearing various substituents such as ester, hydroxyl, amido, pyridyl, thienyl, bulky triphenylamine, fluorine, and trifluoromethyl groups. The high conversions remain almost constant after five cycles. Additionally, the antiepileptic drug (rufinamide) is successfully prepared by a simple one-step reaction using Cu(I)-Bpy-COF, proving its practical feasibility for pharmaceutical synthesis.

Preparation of nanodiamond anchored on copper tannic acid as a heterogenous catalyst for synthesis of 1,4-benzodiazepines derivatives

In this research, a new and eco-friendly heterogeneous catalyst (ND@Tannicacid-Cu) was synthesized based on nanodiamond and copper tannic acid via esterification process. The as-prepared catalyst was characterized by Fourier transforms infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The catalytic efficacy of the intended catalyst was examined by one-step three-component reaction of 1,4-benzodiazepine derivatives from a mixture of ortho-phenylenediamine, aromatic aldehydes, and dimedone under mild conditions. In all instances, corresponding 2,4-benzodiazepines derivatives were synthesized with high efficiency, short reaction time, straightforward work up procedure, no requirement for column-chromatography, and cost-effective catalyst. The heterogeneous catalyst was easily recycled using fillers, and it can be reused for eight cycles without significantly diminishing its performance.

Recent Progress on Synthesis of Functionalized 1,5-Disubstituted Triazoles

Immediately after the invention of 'Click Chemistry' in 2002, the regioselective 1,2,3- triazole scaffolds resulted from respective organic azides and terminal alkynes under Cu(I) catalysis have been well recognized as the functional heterocyclic core at the centre of modern organic chemistry, medicinal chemistry, and material sciences. This CuAAC reaction has several notable features including excellent regioselectivity, high-to-excellent yields, easy to execute, short reaction time, modular in nature, mild condition, readily available starting materials, etc. Moreover, the resulting regioselective triazoles can serve as amide bond isosteres, a privileged functional group in drug discovery and development. More than hundreds of reviews had been devoted to the 'Click Chemistry' in special reference to 1,4-disubstituted triazoles, while only little efforts were made for an opposite regioisomer i.e., 1,5-disubstituted triazole. Herein, we have presented various classical approaches for an expeditious synthesis of a wide range of biologically relevant 1,5- disubstituted 1,2,3-triazole analogues. The syntheses of such a class of diversly functionalized triazoles have emerged as a crucial investigation in the domain of chemistry and biology. This tutorial review covers the literature assessment on the development of various synthetic protocols for the functionalized 1,5-disubstituted triazoles reported during the last 12 years.

Iridium-catalysed thioether-directed regioselective cycloaddition of internal alkynes with azides

We report herein a cationic iridium-catalysed thioether-directed alkyne-azide cycloaddition reaction. Diverse 2-alkynyl phenyl sulfides can undergo cycloaddition with different azides in a regioselective fashion. The reaction features high efficiency, a short reaction time, and a broad substrate scope, providing modular access to complex S-containing triazoles.

Regioselective Synthesis and Molecular Docking Studies of 1,5-Disubstituted 1,2,3-Triazole Derivatives of Pyrimidine Nucleobases

1,2,3-triazoles are versatile building blocks with growing interest in medicinal chemistry. For this reason, organic chemistry focuses on the development of new synthetic pathways to obtain 1,2,3-triazole derivatives, especially with pyridine moieties. In this work, a novel series of 1,5-disubstituted-1,2,3-triazoles functionalized with pyrimidine nucleobases were prepared via 1,3-dipolar cycloaddition reaction in a regioselective manner for the first time. The N1-propargyl nucleobases, used as an alkyne intermediate, were obtained in high yields (87-92%) with a new two-step procedure that selectively led to the monoalkylated compounds. Then, FeCl₃ was employed as an efficient Lewis acid catalyst for 1,3-dipolar cycloaddition between different aryl and benzyl azides and the N1-propargyl nucleobases previously synthesized. This new protocol allows the synthesis of a series of new 1,2,3-triazole derivatives with good to excellent yields (82-92%). The ADME (Absorption, Distribution, Metabolism, and Excretion) analysis showed good pharmacokinetic properties and no violations of Lipinsky's rules, suggesting an appropriate drug likeness for these new compounds. Molecular docking simulations, conducted on different targets, revealed that two of these new hybrids could be potential ligands for viral and bacterial protein receptors such as human norovirus capsid protein, SARS-CoV-2 NSP13 helicase, and metallo-β-lactamase.

Post-Functionalization of Organometallic Complexes via Click-Reaction

CuAAC (Cu catalyzed azide-alkyne cycloaddition) click-reaction is a simple and powerful method for the post-synthetic modification of organometallic complexes of transition metals. This approach allows the selective introduction of additional donor sites or functional groups to the periphery of the ligand environment. This is especially important if a metalloligand with free donor sites, which are of the same nature as the primary site for the coordination of the primary metal, has to be created. The concept of post-synthetic modification of organometallic complexes by click-reaction is relatively recent and the currently available experimental material does not yet allow us to identify trends and formulate recommendations to address specific problems. In the present study, we have applied the CuAAC reaction for the post-synthetic modification of diimine mononuclear complexes Re(I), Pt(II) and Ir(III) with C≡C bonds at the periphery of the ligand environment and demonstrated that click-chemistry is a powerful tool for the tunable chemical post-synthetic modification of coordination compounds.

Copper-Catalyzed Azide–Alkyne Cycloaddition (CuAAC) by Functionalized NHC-Based Polynuclear Catalysts: Scope and Mechanistic Insights

Copper(I) [Cu₂(μ-Br)₂(^tBuImCH₂pyCH₂L)]_n (L = OMe, NEt₂, NH^tBu) compounds supported by flexible functionalized NHC-based polydentate ligands have been prepared in a one-pot procedure by reacting the corresponding imidazolium salt with an excess of copper powder and Ag₂O. An X-ray diffraction analysis has revealed that [Cu₂(μ-Br)₂(^tBuImCH₂pyCH₂NEt₂)]_n is a linear coordination polymer formed by bimetallic [Cu(μ-Br)]₂ units linked by the lutidine-based NHC-py-NEt₂ ligand, which acts as a heteroditopic ligand with a 1κC-2κ²N,N′ coordination mode. We propose that the polymeric compounds break down in the solution into more compact tetranuclear [Cu₂(μ-Br)₂(^tBuImCH₂pyCH₂L)]₂ compounds with a coordination mode identical to the functionalized NHC ligands. These compounds have been found to exhibit high catalytic activity in the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. In particular, [Cu₂(μ-Br)₂(^tBuImCH₂pyCH₂NEt₂)]₂ efficiently catalyzes the click reaction of a range of azides and alkynes, under an inert atmosphere at room temperature in neat conditions at a very low catalyst loading, to quantitatively afford the corresponding 1,4-disubstituted 1,2,3-triazole derivatives in a few minutes. The cycloaddition reaction of benzyl azide to phenylacetylene can be performed at 25–50 ppm catalyst loading by increasing the reaction time and/or temperature. Reactivity studies have shown that the activation of the polynuclear catalyst precursor involves the alkyne deprotonation by the NHC moiety of the polydentate ligand to afford a copper(I)-alkynyl species bearing a functionalized imidazolium ligand. DFT calculations support the participation of the dinuclear species [(CuBr)₂(μ-^tBuImCH₂pyCH₂NEt₂)], resulting from the fragmentation of the tetranuclear compound, as the catalytically active species. The proposed reaction pathway proceeds through zwitterionic dinuclear intermediates and entails the active participation of both copper atoms, as well as the NHC moiety as an internal base, which activates the reacting alkyne via deprotonation.

Seeking heterocyclic scaffolds as antivirals against dengue virus

Dengue is one of the most typical viral infection categorized in the Neglected Tropical Diseases (NTDs). It is transmitted via the female Aedes aegypti mosquito to humans and majorly puts risk to the lives of more than half of the world. Recent advancements in medicinal chemistry have led to the design and development of numerous potential heterocyclic scaffolds as antiviral drug candidates for the inhibition of the dengue virus (DENV). Thus, in this review, we have discussed the significance of inhibitory and antiviral activities of nitrogen, oxygen, and mixed (nitrogen-sulfur and nitrogen-oxygen) heterocyclic scaffolds that are published in the last seven years (2016–2022). Furthermore, we have also discussed the probable mechanisms of action and the diverse structure-activity relationships (SARs) of the heterocyclic scaffolds. In addition, this review has elaborately outlined the mechanism of viral infection and the life cycle of DENV in the host cells. The wide set of heterocycles and their SARs will aid in the development of pharmaceuticals that will allow the researchers to synthesize the promising anti-dengue drug candidate in the future.

Azirine-triazole hybrids: selective synthesis of 5-(2H-azirin-2-yl)-, 5-(1H-pyrrol-2-yl)-1H-1,2,3-triazoles and 2-(5-(2H-azirin-2-yl)-1H-1,2,3-triazol-1-yl)pyridines

Azirine-triazole hybrids, 1-R-5-(3-aryl-2H-azirin-2-yl)-1H-1,2,3-triazoles, were selectively synthesized by reaction of 1-(3-aryl-2H-azirin-2-yl)-2-(triphenylphosphoranylidene)ethanones with tosyl and (E)-2-benzoylvinyl azides in high yields at rt. The reaction with 2-azidopyridine makes it possible to obtain azirine-triazole-pyridine hybrids, albeit in moderate yields, at 170 °C. The mechanism and selectivity of the reaction of α-carbonylphosphoranes with azides are discussed on the basis of DFT calculations. According to the calculation, the reaction of α-carbonylphosphoranes with model mesyl azide, leading to 1,5-disubstituted triazoles proceeds via a non-concerted cycloaddition, while the reaction leading to 1,4-disubstituted triazoles proceeds via a concerted azide cycloaddition, but through the transition state which has much higher energy. In contrast to the reaction of α-(triphenylphosphoranylidene)ketones with TsN₃, the reaction with TfN₃ yields the α-diazo ketones. Ni-Catalyzed reaction of azirinyl-1,2,3-triazoles with acetylacetone provides pyrrole-triazole and pyrrole-triazole-pyridine hybrids in good yields under mild conditions.

Nanomagnetic macrocyclic Schiff-base-Mn(ii) complex: an efficient heterogeneous catalyst for click approach synthesis of novel β-substitued-1,2,3-triazoles

In the present work, a novel symmetrical 15-membered macrocyclic Schiff base complex of manganese was prepared using the reaction of the synthetic 2,6-diacetylpyridine functionalized Fe₃O₄ MNPs with 2,2-(piperazine-1,4-diyl)dianiline and Mn(ii) bromide salt via a template approach. The resulting [Fe₃O₄@PAM-Schiff-base-Mn][ClO₄] heterogenized complex was characterized using FT-IR, XRD, BET, TGA, EDX, Xray-mapping, SEM, TEM and VSM analysis. To demonstrate proof of concept, Huisgen 1,3-dipolar cycloaddition synthesis of 1,2,3-triazoles was selected to evaluate the activity and reusability of the catalyst. The ethanol as a green solvent proved to be an excellent reaction medium for this synthesis. Yields of up to 100% were obtained in some cases. Significantly, as demonstrated, [Fe₃O₄@PAM-Schiff-base-Mn][ClO₄] catalyst was recycled for 8 cycles without losing catalytic activity under the optimized reaction conditions. The hot filtration and ICP-OES tests ratified that there was no leaching of metal during the catalytic reaction, indicating the heterogeneous manner of the catalyst.

Radical borylation of vinyl azides with NHC-boranes: divergent synthesis of α-boryl ketones and borylated triazoles

A divergent radical borylation of vinyl azides with N-heterocyclic carbene (NHC) boranes in the presence of ^tBuSH is described. The protocol enables the divergent synthesis of α-boryl ketones and borylated triazoles with excellent functional group tolerance and a broad substrate scope. Remarkably, this work shows that vinyl azides can serve as unprecedented five-atom synthons for the construction of 1,2,3-triazoles without N₂ extrusion.

Recent Advances in Copper-Based Solid Heterogeneous Catalysts for Azide-Alkyne Cycloaddition Reactions

The copper(I)-catalyzed azide−alkyne cycloaddition (CuAAC) reaction is considered to be the most representative ligation process within the context of the “click chemistry” concept. This CuAAC reaction, which yields compounds containing a 1,2,3-triazole core, has become relevant in the construction of biologically complex systems, bioconjugation strategies, and supramolecular and material sciences. Although many CuAAC reactions are performed under homogenous conditions, heterogenous copper-based catalytic systems are gaining exponential interest, relying on the easy removal, recovery, and reusability of catalytically copper species. The present review covers the most recently developed copper-containing heterogenous solid catalytic systems that use solid inorganic/organic hybrid supports, and which have been used in promoting CuAAC reactions. Due to the demand for 1,2,3-triazoles as non-classical bioisosteres and as framework-based drugs, the CuAAC reaction promoted by solid heterogenous catalysts has greatly improved the recovery and removal of copper species, usually by simple filtration. In so doing, the solving of the toxicity issue regarding copper particles in compounds of biological interest has been achieved. This protocol is also expected to produce a practical chemical process for accessing such compounds on an industrial scale.

Tandem amide coupling and hydroamination: unexpected benzotriazole oxide addition to the propiolic acid triple bond

An unexpected tandem reaction consisting of amide coupling and hydroamination occurring with common triazole coupling reagents.

Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC≡CSiMe₃ are also reported. They are three-coordinate copper complexes featuring η²-bound alkynes. Raman data show significant red-shifts in C≡C stretch of [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CH) and [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CSiMe₃) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu₂(μ-[3,5-(CF₃)₂Pz])₂(HC≡CH)₂ display similar Cu-alkyne bonding features. The mononuclear [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF₃)₂Pz]Cu}₃ involving bridging pyrazolates.

Ultrasound-assisted synthesis of pyrimidines and their fused derivatives: A review

The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.

Diorganyl diselenides: a powerful tool for the construction of selenium containing scaffolds

Organoselenium compounds find versatile applications in organic synthesis, materials synthesis, and ligand chemistry. Organoselenium heterocycles are widely studied agents with diverse applications in various biological processes. This review highlights the recent progress in the synthesis of selenium heterocycles using diorganyl diselenides with keen attention on green synthetic approaches, scopes, C-H selanylation, the mechanisms of different reactions and insights into the formation of metal complexes. The C-H selanylation using diorganyl diselenides with different catalysts, bases, transition metals, iodine salts, NIS, hypervalent iodine, and other reagents is summarised. Finally, the diverse binding modes of bis(2/4-pyridyl)diselenide with different metal complexes are also summarised.

Recent Progress in Catalytic Synthesis of 1,2,3-Triazoles

1,2,3-triazoles represent a functional heterocyclic core that has been at the center of modern organic chemistry since the beginning of click chemistry. Being a versatile framework, such an aromatic ring can be observed in uncountable molecules useful in medicine and photochemistry, just to name a few. This review summarizes the progress achieved in their synthesis from 2015 to today, with particular emphasis on the development of new catalytic and eco-compatible approaches. In doing so, we subdivided the report based on their degree of functionalization and, for each subparagraph, we outlined the role of the catalyst employed.

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

Diverse strategies for the efficient and attractive synthesis of a wide variety of relevant 1,4,5-trisubstituted 1,2,3-triazole molecules are reported. The synthesis of this category of diverse fully functionalized 1,2,3-triazoles has become a necessary and unique research subject in modern synthetic organic key transformations in academia, pharmacy, and industry. The current review aims to cover a wide literature survey of numerous synthetic strategies. Recent reports (2017–2021) in the field of 1,4,5-trisubstituted 1,2,3-triazoles are emphasized in this current review.

Sc(OTf)3-Catalyzed Formal [3 + 3] Cycloaddition Reaction of Diaziridines and Quinones for the Synthesis of Benzo[e][1,3,4]oxadiazines

A formal [3 + 3] cyclization reaction of diaziridines and quinones has been developed offering 1,3,4-oxadiazinanes in generally high yields (up to 96%). The reaction was catalyzed by Sc(OTf)₃ with a large substrate scope for both diaziridines and quinones. The synergistic activation of 1,3-dipolar diaziridines and the dipolar quinones was found to be essential to enable this reaction.

Triazole-containing hybrids with anti-Mycobacterium tuberculosis potential - Part I: 1,2,3-Triazole

Tuberculosis regimens currently applied in clinical practice require months of multidrug therapy, which imposes a major challenge of patient compliance and drug resistance development. Moreover, because of the increasing emergence of hard-to-treat tuberculosis, this disease continues to be a significant threat to the human population. 1,2,3-triazole as a privileged structure has been widely used as an effective template for drug discovery, and 1,2,3-triazole-containing hybrids that can simultaneously act on dual or multiple targets in Mycobacterium tuberculosis have the potential to circumvent drug resistance, enhance efficacy, reduce side effects and improve pharmacokinetic as well as pharmacodynamic profiles. Thus, 1,2,3-triazole-containing hybrids are useful scaffolds for the development of antitubercular agents. This review aims to highlight recent advances of 1,2,3-triazole-containing hybrids with potential activity against various forms of M. tuberculosis, covering articles published between 2015 and 2020. The structure-activity relationship and the mechanism of action are also discussed to facilitate further rational design of more effective drug candidates.

Synthesis, in-vitro evaluation, molecular docking, and kinetic studies of pyridazine-triazole hybrid system as novel α-glucosidase inhibitors

In this study, we reported the discovery of pyridazine based 1,2,3-triazole derivatives as inhibitors of α-glucosidase. All target compounds exhibited significant inhibitory activities against yeast and rat α-glucosidase enzymes compared to positive control, acarbose. The most potent compound 6j, ethyl 3-(2-(1-(4-nitrobenzyl)-1H-1,2,3-triazol-4-yl)ethyl)-5,6-diphenylpyridazine-4-carboxylate exhibited IC₅₀ values of 58, and 73 µM. Docking studies indicated the responsibility of hydrophobic and hydrogen bonding interactions in the ligand-enzyme complex stability. The in-vitro safety against the normal cell line was observed by toxicity evaluation of the selected compounds.

Synthesis of heteroleptic phosphine–copper(i) complexes: fluorescence sensing and catalytic properties

A series of heteroleptic Cu(i) complexes were precisely synthesized using different bipyridine and diphosphine ligands. These complexes exhibited fluorescence sensing towards silver ions and high catalytic activity towards the CuAAC reaction.

Self-assembly of cuprous iodide cluster-based calix[4]resorcinarenes and photocatalytic properties

Cluster-based complexes 1 and 2 with [Cu6I5] and [Cu8I8] polynuclear motifs were constructed via a conformation-adaptive self-assembly strategy, respectively. Two Cu(i) complexes exhibited photocatalytic activity to the CuAAC reaction in water solution.

A novel synthetic acanthoic acid analogues and their cytotoxic activity in cholangiocarcinoma cells

A novel series of acanthoic acid analogues containing triazole moiety were synthesized through esterification and CuAAC reaction. Evaluation of their biological activities against four cell lines of cholangiocarcinoma cells showed that 3d exhibited the strongest activity with an IC₅₀ value of 18 µM against KKU-213 cell line, which was 8 fold more potent than acanthoic acid. Interestingly, the triazole ring and nitro group on benzyl ring play very significant role in cytotoxic activity. The computational studies revealed that 3d occupies the binding energy of -12.7 and -10.8 kcal/mol with CDK-2 and EGFR protein kinases, respectively. This result might provide a beginning for the development of acanthoic acid analogues as an anticancer agent.

Microwave-Assisted Synthesis of Quinazolines and Quinazolinones: An Overview

Microwave irradiation (MWI), as a unique, effective, sustainable, more economic, and greener source of energy compared to conventional heating, is applied in different organic transformations to result in the rapid formation of desired compounds due to thermal/kinetic effects. In this review, we try to underscore the applications of microwave irradiation (MWI) in the synthesis of quinazoline and quinazolinone derivatives that have been achieved and reported on in the last two decades.

Access to α-Pyrazole and α-Triazole Derivatives of Ketones from Oxidative Heteroarylation of Silyl Enolethers

The synthesis of α-pyrazole and α-triazole derivatives of ketones by the ceric ammonium nitrate-mediated oxidative coupling of enolsilanes with heteroarenes is reported. The reaction proceeds under mild reaction conditions to provide a diversity of products, including sterically hindered fully substituted derivatives.

Benefits and applications of microwave-assisted synthesis of nitrogen containing heterocycles in medicinal chemistry

Nitrogen containing heterocycles are of immense research interest because they are often found as naturally occurring bioactive compounds.