Synthesis of 4-Aryl-1H-1,2,3-triazoles through TBAF-Catalyzed [3 + 2] Cycloaddition of 2-Aryl-1-nitroethenes with TMSN3 under Solvent-Free Conditions

An Atom-Economic Method for 1,2,3-Triazole Derivatives via Oxidative [3 + 2] Cycloaddition Harnessing the Power of Electrochemical Oxidation and Click Chemistry

An electrochemical method was developed to accomplish the reagentless synthesis of 4,5-disubstituted triazole derivatives employing secondary propargyl alcohol as C-3 synthon and sodium azide as cycloaddition counterpart. The reaction was conducted at room temperature in an undivided cell with a constant current using a pencil graphite (C) anode and stainless-steel cathode in a MeCN solvent system. The proposed reaction mechanism was convincingly established by carrying out a series of control experiments and further supported by electrochemical and density functional theory (DFT) studies.

Organocatalyzed Regioselective Synthesis of 1,5-Disubstituted 1,2,3-Triazolyl Glycoconjugates

A novel organocatalyzed [3+2] cycloaddition reaction of nitroolefins with glycosyl azides as well as organic azides has been developed for successful construction of 1,5-disubstituted triazolyl glycoconjugates. This metal-free and acid-free, regioselective synthetic protocol proceeds in the presence of only Schreiner thiourea organocatalysts, which enable the required activation of nitroolefins through double hydrogen bonding. The straightforward, operationally simple, and regioselectivity of this methodology, complementing to the classical RuAAC catalyzed synthesis of 1,5-disubstituted 1,2,3-triazoles. In the presence of catalytic amount of Schreiner thiourea organocatalyst, organic azides react with a broad array of nitroolefins producing a series of diverse 1,5-disubstituted 1,2,3- triazoles in good yields with excellent regioselectivity.

Mechanistic Aspects on [3+2] Cycloaddition (32CA) Reactions of Azides to Nitroolefins: A Computational and Kinetic Study

[3+2] cycloadditions of nitroolefins have emerged as a selective and catalyst-free alternative for the synthesis of 1,2,3-triazoles from azides. We describe mechanistic studies into the cycloaddition/rearomatization reaction sequence. DFT calculations revealed a rate-limiting cycloaddition step proceeding via an asynchronous TS with high kinetic selectivity for the 1,5-triazole. Kinetic studies reveal a second-order rate law, and ¹³ C kinetic isotopic effects at natural abundance were measured with a significant normal effect at the conjugated olefinic centers of 1.0158 and 1.0216 at the α and β-carbons of β-nitrostyrene. Distortion/interaction-activation strain and energy decomposition analyses revealed that the major regioisomeric pathway benefits from an earlier and less-distorted TS, while intermolecular interaction terms dominate the preference for 1,5- over 1,4-cycloadducts. In addition, the major regioisomer also has more favorable electrostatic and dispersion terms. Additionally, while static DFT calculations suggest a concerted but highly asynchronous Ei-type HNO₂ elimination mechanism, quasiclassical direct-dynamics calculations reveal the existence of a dynamic intermediate.

Intercepting the Banert cascade with nucleophilic fluorine: direct access to α-fluorinated NH-1,2,3-triazoles

The treatment of propargylic azides with silver(i) fluoride in acetonitrile was found to yield α-fluorinated NH-1,2,3-triazoles via the Banert cascade. The reaction was regioselective and the products result from an initial [3,3] rearrangement. The reaction is demonstrated on >15 examples with yields ranging from 37% to 86%.

Silver Mediated Banert Cascade with Carbon Nucleophiles

The Banert cascade of propargylic azides can be promoted by simple silver salts, and the triazafulvene intermediate can be intercepted by carbon nucleophiles. Various indoles (>25 examples, up to 92% yield) and electron-rich heterocycles were effective. The Mayr nucleophilicity parameter (N) was found to correlate to the reaction efficiency, which enabled the formation of C_sp³-C_sp² and C_sp³-C_sp³ bonds under otherwise identical conditions from structurally dissimilar nucleophiles.

Tetraamminecopper(II) Sulfate Monohydrate in Oxidative Azide-olefin Cyclo-addition and Three-component Click Reaction

INTRODUCTION

An effective Cu-complex, [Cu(NH3)4SO4 • H2O] was prepared conveniently from the inexpensive and easily available starting reagents in a simple route.

MATERIALS AND METHODS

Excellent reactivity of the catalyst was observed towards two competent clickcycloadditions: (a) oxidative cycloaddition of azides with electron-poor olefins and (b) one-pot cycloaddition of alkynes with boronic acid and sodium azide under "click-appropriate" conditions.

RESULTS

No external oxidant, short reaction time, high product yield, wide substrate scope, and aqueous solvent media make the azide-olefin cycloaddition approach a greener route in contrast to the reported methods.

CONCLUSION

The newly developed mild, green, and rapid three-component strategy shows product diversity with superb yields at room temperature by reducing the synthetic process time and using only 1 mol % of the synthesized copper complex.

Pharmacological and Cellular Significance of Triazole-Surrogated Compounds

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Heterocyclic compounds have been at the hierarchy position in academia, and industrial arena, particularly the compounds containing triazole-core are found to be potent with a broad range of biological activities. The resistance of triazole ring towards chemical (acid and base) hydrolysis, oxidative and reductive reaction conditions, metabolic degradation and its higher aromatic stabilization energy makes it a better heterocyclic core as therapeutic agents. These triazole-linked compounds are used for clinical purposes for antifungal, anti-mycobacterium, anticancer, anti-migraine and antidepressant drugs. Triazole scaffolds are also found to act as a spacer for the sake of covalent attachment of the high molecular weight bio-macromolecules with an experimental building blocks to explore structure-function relationships. Herein, several methods and strategies for the synthesis of compounds with 1,2,3-triazole moiety exploring Hüisgen, Meldal and Sharpless 1,3-dipolar cycloaddition reaction between azide and alkyne derivatives have been deliberated for a series of representative compounds. Moreover, this review article highlights in-depth applications of the [3+2]-cycloaddition reaction for the advances of triazole-containing antibacterial as well as metabolic labelling agents for the in vitro and in vivo studies on cellular level.

Regioselective N1- and N2-heterocycloalkylation of N1-sulfonyl-1,2,3-triazoles

A tuneable and visible-light-driven three-component reaction between N¹-sulfonyl-1,2,3-triazoles, saturated heterocycles, and N-bromosuccinimide for regioselective synthesis of N¹- or N²-heterocycloalkylated 1,2,3-triazoles.

Regioselective synthesis of 4-fluoro-1,5-disubstituted-1,2,3-triazoles from synthetic surrogates of α-fluoroalkynes

This TFA-catalyzed [3+2] cycloaddition of organic azides with α-fluoronitroalkenes, used as synthetic surrogates of α-fluoroalkynes, provides a new route to multi-substituted fluorotriazoles with broader substrate scopes and high regioselectivity.

Synthesis of 1,5-Functionalized 1,2,3-Triazoles Using Ionic Liquid/Iron(III) Chloride as an Efficient and Reusable Homogeneous Catalyst

An efficient, eco-compatible, and very cheap method for the construction of triazoles via eliminative azide–olefin cycloaddition (EAOC) reaction has been developed by a catalytic system, IL/FeCl3, offering a highly regioselective approach to structurally diverse 1,5-disubstituted 1,2,3-triazoles in up to 95% yield. This strategy features the reuse of a catalytic system through simple operations. Mechanistic studies indicated that an asynchronous concerted dipolar cycloaddition–elimination process might be involved.

Copper-catalyzed decarboxylative regioselective synthesis of 1,5-disubstituted 1,2,3-triazoles

A copper-catalyzed decarboxylative regioselective protocol for the synthesis of 1,5-disubstituted 1,2,3-triazoles via direct annulation of cinnamic acids with aryl azides has been developed. This is the first example of 1,5-disubstituted 1,2,3-triazoles using Cu(ii) as the catalyst, which were generally synthesized using a ruthenium(ii) catalyst.

An efficient synthesis of 4,5-disubstituted-2H-1,2,3-triazoles from nitroallylic derivatives via a cycloaddition–denitration process

A variety of nitroallylic derivatives were smoothly reacted with sodium azide in the presence of p-TsOH to form synthetically-viable triazoles.

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

The amide moiety of peptides can be replaced for example by a triazole moiety, which is considered to be bioisosteric. Therefore, the carbonyl moiety of an amino acid has to be replaced by an alkyne in order to provide a precursor of such peptidomimetics. As most amino acids have a chiral center at Cα, such amide bond surrogates need a chiral moiety. Here the asymmetric synthesis of a set of 24 N-sulfinyl propargylamines is presented. The condensation of various aldehydes with Ellman's chiral sulfinamide provides chiral N-sulfinylimines, which were reacted with (trimethylsilyl)ethynyllithium to afford diastereomerically pure N-sulfinyl propargylamines. Diverse functional groups present in the propargylic position resemble the side chain present at the Cα of amino acids. Whereas propargylamines with (cyclo)alkyl substituents can be prepared in a direct manner, residues with polar functional groups require suitable protective groups. The presence of particular functional groups in the side chain in some cases leads to remarkable side reactions of the alkyne moiety. Thus, electron-withdrawing substituents in the Cα-position facilitate a base induced rearrangement to α,β-unsaturated imines, while azide-substituted propargylamines form triazoles under surprisingly mild conditions. A panel of propargylamines bearing fluoro or chloro substituents, polar functional groups, or basic and acidic functional groups is accessible for the use as precursors of peptidomimetics.

Copper-Catalyzed Cross-Dehydrogenative N2-Coupling of NH-1,2,3-Triazoles with N,N -Dialkylamides: N-Amidoalkylation of NH-1,2,3-Triazoles

An efficient copper-catalyzed C-N bond formation by N-H/C-H cross-dehydrogenative coupling (CDC) between NH-1,2,3-triazoles and N,N-dialkylamides has been developed. The method provided N-amidoalkylated 1,2,3-triazoles with moderate to high yields, and the reactions showed high N²-selectivities when 4,5-disubstituted NH-1,2,3-triazoles served as the substrates.

Unexpected course of reaction between (E)-2-aryl-1-cyano-1-nitroethenes and diazafluorene: why is there no 1,3-dipolar cycloaddition?

ABSTRACT

Reactions between (E)-2-aryl-1-cyano-1-nitroethenes and diazafluorene lead to acyclic 2,3-diazabuta-1,3-diene derivatives, instead of the expected pyrazoline systems. DFT calculations suggest that this is a consequence of formation of zwitterionic structure in the first stage of the reaction. It must be noted that this is a specific property of the (E)-2-aryl-1-cyano-1-nitroethenes group, in contrast to most other conjugated nitroalkenes.

GRAPHICAL ABSTRACT

Base-Promoted Synthesis of N-Substituted 1,2,3-Triazoles via Enaminone-Azide Cycloaddition Involving Regitz Diazo Transfer

The domino reactions between NH-based secondary enaminones and tosyl azide have been developed for the synthesis of various N-substituted 1,2,3-triazoles by employing t-BuONa as the base promoter. Through a key Regitz diazo-transfer process with tosyl azide, the reactions proceed efficiently at room temperature with good substrate tolerance.

Click-chemistry approaches to π-conjugated polymers for organic electronics applications

Given the wide utility of click-chemistry reactions for the preparation of simple moieties within large architecturally complex materials, this minireview article aims at surveying papers exploring their scope in the area of π-conjugated polymers for application in organic electronics to enable advanced functional properties.

Organocatalytic routes toward substituted 1,2,3-triazoles

The present feature article describes the different organocatalytic routes for the synthesis of substituted 1,2,3-triazoles. This methodology has recently gained much attention due to its many advantages like high regioselectivity, substrate scope, high yields, and access to novel molecules. The review is divided into 4 different sections based on the active intermediate of the triazole synthesis reactions. The mechanism of each approach is critically discussed and in addition, the advantages and disadvantages of each method are described with relevant examples.

A single-step acid catalyzed reaction for rapid assembly of NH-1,2,3-triazoles

NH-1,2,3-Triazole moieties are a part of the design of various biologically active compounds, pharmaceutical agents and functional materials.

One-pot four component domino strategy for the synthesis of novel spirooxindole pyrrolizine linked 1,2,3-triazoles via stereo- and regioselective [3 + 2] cycloaddition reaction in acidic medium

An efficient, one-pot four component condensation has been reported for the synthesis of spirooxindole pyrrolizine linked 1,2,3-triazolesvia[3 + 2] cycloaddition. The structures were confirmed by¹H NMR,¹³C NMR, mass spectra and X-ray.

1,4-Dihydroxyanthraquinone–copper(ii) supported on superparamagnetic Fe3O4@SiO2: an efficient catalyst for N-arylation of nitrogen heterocycles and alkylamines with aryl halides and click synthesis of 1-aryl-1,2,3-triazole derivatives

1,4-Dihydroxyanthraquinone–copper(ii) supported on superparamagnetic Fe₃O₄@SiO₂ catalyst was employed for the N-arylation of nitrogen heterocycles and alkylamines.