Effect of temperature on triazole and bistriazole formation through copper-catalyzed alkyne–azide cycloaddition

Each Interruption is an Opportunity: Novel Synthetic Strategies Explored Through Interrupted Click Reactions

The particular and unique mechanism of the copper-catalyzed reaction between azides and alkynes (CuAAC) has not only allowed for the efficient synthesis of 1,2,3-trisubstituted 1,4-triazoles in excellent yields and under mild conditions, becoming the quintessential click reaction, but it has also enabled the straightforward formation of a metallocycle intermediate, the copper triazolyl. This, under suitable reaction conditions able to suppress its protonolysis, can be used either for the creation of new bicyclic triazolyl structures or for the generation of novel three or four-component reactions. The aim of this review is to rationalize and unify all these transformations, which are collectively referred to as "interrupted click reactions".

Copper-Mediated Synthesis of (E)-1-Azido and (Z)-1,2-Diazido Alkenes from 1-Alkene-1,2-diboronic Esters: An Approach to Mono- and 1,2-Di-(1,2,3-Triazolyl)-Alkenes and Fused Bis-(1,2,3-Triazolo)-Pyrazines

A stereoselective and convenient route has been demonstrated to access (Z)-1,2-diazido alkenes from the corresponding 1,2-diboronic esters via a copper-mediated reaction with sodium azide. Alternately, mono-functionalization was regioselectively carried out with trimethylsilyl azide as an azidation reactant. The in situ conversion of bis-azides to the corresponding bis-triazoles can be readily achieved in the presence of copper sulfate and sodium ascorbate, while the modification of the catalytic system opened a new convenient route to bis-triazolo-pyrazines, a new class of fused heterocycles.

Water-Compatible Synthesis of 1,2,3-Triazoles under Ultrasonic Conditions by a Cu(I) Complex-Mediated Click Reaction

A new monophosphine Cu(I) complex bearing bis(pyrazolyl)methane (L 1 ) (CuIL 1 PPh 3 ) was synthesized and used as a catalyst for the three-component click reaction from an alkyl halide, sodium azide, and terminal alkyne to furnish 1,4-disubstituted 1,2,3-triazoles in up to 93% yield. The catalyst is highly stable, compatible with oxygen/water, and works with total efficiency under ultrasonic condition. The structure of the complex was studied and confirmed by X-ray crystallography, finding a riveting relationship with its catalytic activity. This sustainable triazoles synthesis is distinguished by its high atom economy, low catalyst loading (up to 0.5 mol %), broad substrate scope, short reaction times, operational simplicity, and an easy gram-scale supply of a functionalized product for subsequent synthetic applications.

5-Formyltriazoles as Valuable Starting Materials for Unsymmetrically Substituted Bi-1,2,3-Triazoles

Herein, we present the first synthetic methodologies toward non-symmetrical 5,5′-C, C-linked bi-1,2,3-triazoles starting from 5-formyl-1,2,3-triazole via two related pathways. In a first reaction, 5-formyl-1,2,3-triazole is successfully reacted with a variety of nitroalkanes and organic azides in a one-pot three-component fashion resulting in tetra-ortho-substituted bi-1,2,3-triazoles. In the second, closely related reaction, 5-formyl-1,2,3-triazole is initially converted with nitromethane to the corresponding nitroalkene, and then subsequently oxidatively cyclized with a number of organic azides toward 4-nitro substituted non-symmetrical tetra-ortho-substituted 5,5′-bi-1,2,3-triazoles. The scope of both reactions and furtherr post-functionalizations are examined, and the atropisomeric properties of the obtained bi-1,2,3-triazoles are evaluated.

CuII -Catalyzed Oxidative Formation of 5-Alkynyltriazoles

In an alcoholic solvent under the catalysis of Cu(OAc)₂ ⋅H₂ O, organic azide and terminal alkyne could oxidatively couple to afford 5-alkynyl-1,2,3-triazole (alkynyltriazole) at room temperature under an atmosphere of O₂ in a few hours. The involvement of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) is essential, without which the redox neutral coupling instead proceeds to produce 5-H-1,2,3-triazole (protiotriazole) as the major product. Therefore, DBN switches the redox neutral coupling between terminal alkyne and organic azide, the copper-catalyzed "click" reaction to afford protiotriazole, to an oxidation reaction that results in alkynyltriazole. The organic base DBN is effective in accelerating the copper(II)-catalyzed oxidation of terminal alkyne or copper(I) acetylide, which is intercepted by an organic azide to produce alkynyltriazole. The proposed mechanistic model suggests that the selectivity between alkynyl- and protiotriazole, and other acetylide or triazolide oxidation products is determined by the competition between copper(I)-catalyzed redox neutral cycloaddition and copper(II)/O₂ -mediated acetylide oxidation after the formation of copper(I) acetylide.

Evaluation of the effect of 1,3-bis-(4-phenyl-[1,2,3] triazole-1-il)2-propanol in comparison with metronidazole in an in vitro culture of Blastocystis in samples of patients with irritable bowel syndrome

Metronidazole is the most-used pharmaceutical for the treatment of infection by Blastocystis. However, studies have reported resistance of the microorganism towards this pharmaceutical. In Mexico, studies concerning the prevalence of this parasite and its relationship to Irritable Bowel Syndrome have been carried out. To evaluate the in vitro effect of metronidazole and the compound 1,3-bis-(4-phenyl-[1,2,3] triazole-1-il)2-propanol over Blastocystis, as well as the prevalence of Blastocystis in patients with Irritable Bowel Syndrome. A prospective, transversal design study (April 2016-April 2017) of 51 samples of patients with Irritable Bowel Syndrome, obtained from the ISSEMyM Medical Center in Toluca, Mexico. For the identification of Blastocystis was done in three serial stool samples through direct microscopic examination and the Ritchie technique. The in vitro susceptibility test towards metronidazole and the triazolic compound was done through a microculture in concentrations of 1 to 1000 µg/mL, each one in triplicate. A 31.3% prevalence of Blastocystis was observed in the population, with greater prevalence in women (30.2%) than in men (25%). In the susceptibility test, a CL50 of 64 µg/mL was obtained for metronidazole, in comparison to the CL50 of 250 µg/mL for 1,3-bis-(4-phenyl-[1,2,3] triazole-1-il)2-propanol. This molecule in development has an effect for the treatment of infection by Blastocystis in vitro in patients with IBS and therefore, more studies should be performed.

Arylhydrazone ligands as Cu-protectors and -catalysis promoters in the azide-alkyne cycloaddition reaction

A series of water soluble copper(ii) complexes, [Cu(κO¹O²N-H₂L¹)(H₂O)₂]·2H₂O (2), [Cu(κO-H₃L¹)₂(H₂O)₄] (3), [Cu(κO-H₄L²)₂(H₂O)₄] (5) and [Cu(H₂O)₆]·2H₂L³·2(CH₃)₂NCHO (7), were prepared by the reaction of Cu(NO₃)₂·3H₂O with sodium (Z)-2-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)benzenesulfonate, [Na(μ₄-1:2κO¹,2κO²,3κO³,4κO⁴-H₃L¹)]_n (1; for 2 and 3), sodium (Z)-3-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)-4-hydroxybenzene-sulfonate, [Na(μ-1κO¹,2κO²-H₄L²)]₂ (4; for 5) or sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazineyl)naphthalene-1-sulfonate, [Na(μ-1κO¹O²,2κO³-H₂L³)(CH₃OH)₂]₂ (6; for 7). Compounds 1-7 were fully characterized, also by single-crystal X-ray diffraction analysis, and applied as homogeneous catalysts for the azide-alkyne cycloaddition (AAC) reaction to afford 1,4-disubstituted 1,2,3-triazoles. A structure-catalytic activity relationship has been recognized for the first time on the basis of the occurrence of resonance- and charge-assisted hydrogen bond interactions (RAHB and CAHB), in charge and ligand binding modes, enabling the catalytic activity of the compounds to be ordered as follows: Cu(NO₃)₂≪7 (complex salt with RAHB and CAHB) < 3 (with RAHB and CAHB) < 5 (with RAHB) < 2 (neither RAHB nor CAHB). Complex 2, without such non-covalent interactions, was found to be the most efficient catalyst for the AAC reaction, affording up to 98% product yield after being placed for 15 min, at 125 °C, in a water/acetonitrile mixture under low power (10 W) MW irradiation.

Copper-catalyzed Convenient Synthesis and SAR Studies of Substituted-1,2,3-triazole as Antimicrobial Agents

Background:

A novel copper-catalyzed synthesis of substituted-1,2,3-triazole derivatives has been developed and performed by Huisgen 1,3-dipolar cycloaddition reaction of azides with alkynes. The reaction is one-pot multicomponent.

Objective:

We state the advancement and execution of a methodology allowing for the synthesis of some new substituted 1,2,3-triazole analogues with antimicrobial activity.

Methods:

A series of triazole derivatives was synthesized by Huisgen 1,3-dipolar cycloaddition reaction of azides with alkynes. The structures of the synthesized compounds were elucidated and confirmed by 1H NMR, IR, MS and elemental analysis. All the synthesized compounds were tested for their antimicrobial activity against a series of strains of Bacillus subtilis, Staphylococcus aureus and Escherichia coli for antibacterial activity and against the strains of Candida albicans, Aspergillus flavus and Aspergillus nigar for antifungal activity, respectively.

Results and Conclusion:

From the antimicrobial data, it was observed that all the newly synthesized compounds showed good to moderate level of antibacterial and antifungal activity.

1-(2-Chlorobenzyloxy)-3-[1,2,3]triazol-1-yl-propan-2-ol Derivatives: Synthesis, Characterization, and DFT-Based Descriptors Analysis

A novel series of 1-(2-chlorobenzyloxy)-3-[1,2,3]triazol-1-yl-propan-2-ol derivatives was designed and synthesized using copper catalyzed alkyne-azide cycloaddition in the key step. Theoretical investigation of molecular and electronic properties by means of global and local reactivity indexes of the synthetized compounds was carried out, using DFT (Density Functional Theory) at PBEPBE/6-31++G⁎⁎level.

5,5′-Bistriazoles as axially chiral, multidentate ligands: synthesis, configurational stability and catalytic application of their scandium(iii) complexes

The design and development of 5,5′-bistriazoles featuring aminomethyl substituents is discussed.

When CuAAC 'Click Chemistry' goes heterogeneous

Within the green chemistry context, heterogeneous catalysis is more and more applied to organic synthesis. The well known ‘click chemistry’ and especially its flagship, the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC), is now catch up by such heterogenisation process and copper ions or metals have been grafted or deposited on or into various solids, such as (bio)polymers, charcoal, silica, zeolites, POM or MOF.

Copper immobilized ferromagnetic nanoparticle triazine dendrimer (FMNP@TD–Cu(ii))-catalyzed regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles

The synthesis, characterisation and catalytic activity of FMNP@TD–Cu(ii) for the synthesis of 1,4-disubstituted 1,2,3-triazoles are reported.

Synthesis of bi- and bis-1,2,3-triazoles by copper-catalyzed Huisgen cycloaddition: A family of valuable products by click chemistry

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction, also known as click chemistry, has become a useful tool for the facile formation of 1,2,3-triazoles. Specifically, the utility of this reaction has been demonstrated by the synthesis of structurally diverse bi- and bis-1,2,3-triazoles. The present review focuses on the synthesis of such bi- and bistriazoles and the importance of using copper-promoted click chemistry (CuAAC) for such transformations. In addition, the application of bitriazoles and the related CuAAAC reaction in different fields, including medicinal chemistry, coordination chemistry, biochemistry, and supramolecular chemistry, have been highlighted.

Double [3 + 2]-dimerisation cascade synthesis of bis(triazolyl)bisphosphanes, a new scaffold for bidentate bisphosphanes

A highly convergent synthesis of bis(triazolylphosphane oxides) was developed by a tandem copper-mediated Huisgen reaction-oxidative coupling. The phosphane oxides were reduced by trichlorosilane and the coordination of the resulting bisphosphanes was studied with various transition metals.

Magnetic nano-Fe3O4@TiO2/Cu2O core–shell composite: an efficient novel catalyst for the regioselective synthesis of 1,2,3-triazoles using a click reaction

An efficient and recoverable core–shell nanomagnetic composite was developed for regioselective synthesis of 1,2,3-triazoles using a green procedure.

Preliminary investigations into triazole derived androgen receptor antagonists

A range of 1,4-substituted-1,2,3-N-phenyltriazoles were synthesized and evaluated as non-steroidal androgen receptor (AR) antagonists. The motivation for this study was to replace the N-phenyl amide portion of small molecule antiandrogens with a 1,2,3-triazole and determine effects, if any, on biological activity. The synthetic methodology presented herein is robust, high yielding and extremely rapid. Using this methodology a series of 17 N-aryl triazoles were synthesized from commercially available starting materials in less than 3h. After preliminary biological screening at 20 and 40 μM, the most promising three compounds were found to display IC50 values of 40-50 μM against androgen dependent (LNCaP) cells and serve as a starting point for further structure-activity investigations. All compounds in this work were the focus of an in silico study to dock the compounds into the human androgen receptor ligand binding domain (hARLBD) and compare their predicted binding affinity with known antiandrogens. A comparison of receptor-ligand interactions for the wild type and T877A mutant AR revealed two novel polar interactions. One with Q738 of the wild type site and the second with the mutated A877 residue.

BINOL-linked 1,2,3-triazoles: an unexpected fluorescent sensor with anion–π interaction for iodide ions

BINOL-derived triazoles could be used in organocatalytic silylation and unexpectedly as fluorescent sensors for the recognition of I⁻.

Alkyne-azide cycloaddition catalyzed by silver chloride and "abnormal" silver N-heterocyclic carbene complex

A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields.

Catalytic activity of dithioic acid copper complexes in the alkyne–azide cycloaddition

Diverse dithioic acid copper complexes exhibit a high catalytic activity in the copper-catalyzed alkyne–azide cycloaddition using several solvents under different temperatures, showing a high efficiency with only 0.005 mmol catalyst/mmol alkyne or less. A dithioic acid copper complex derived from acetophenone was selected and used as the catalyst in the preparation of a library of 1,4-disubstituted-1,2,3-triazoles. This process occurred in high yields and good functional group tolerance.