Regioselective synthesis of 1,4‐disubstituted triazoles using bis[(L)prolinato‐N,O]Zn complex as an efficient catalyst in water as a sole solvent

A concise, convenient and mild route for one‐pot regioselective synthesis of N‐aryl‐ and N‐alkyltriazoles in water as a sole solvent is reported. The methodology involves a three‐component reaction comprising aryl/alkyl‐alkyne, sodium azide and aryl/alkyl/allyl halide catalyzed by zinc(II) L ‐prolinate. Prominent features of our protocol are incorporation of transition metal catalyst other than copper, water as the reaction medium, recyclability of catalyst and avoidance of hazardous aryl azide as a reactant. Copyright © 2011 John Wiley & Sons, Ltd.     

Functionalized graphene oxide supported copper (I) complex as effective and recyclable nanocatalyst for one‐pot three component synthesis of 1,2,3‐triazoles

Efficient, one pot three‐component reaction of alkyl halides, sodium azide with terminal alkynes can be catalyzed by functionalized graphene oxide with copper(I) under thermal conditions. A series of 1,4‐disubstituted 1,2,3‐triazoles were obtained by this one‐pot strategy. The catalyst was prepared and characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), emission scanning electron microscopy (FE‐SEM) and energy dispersive X‐ray (EDX). The catalyst can be reused at least five times without significant deactivation.     

Copper immobilized onto polymer‐coated magnetic nanoparticles as recoverable catalyst for ‘click’ reaction

Copper supported on polymer‐coated magnetic nanoparticles was designed and synthesized as a separable heterogeneous catalyst. The catalyst was fully characterized using several techniques such as Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, scanning and transmission electron microscopies, X‐ray diffraction, vibrating sample magnetometry, thermogravimetric analysis and inductively coupled plasma atomic emission spectrometry. All results showed that copper was successfully supported on the polymer‐coated magnetic nanoparticles. Also, results showed that the synthesized material can be used as an efficient catalyst for the preparation of a series of 1,4‐disubstituted 1,2,3‐triazoles from corresponding halides, alkynes and sodium azide. The catalyst can be easily isolated from the reaction solution by applying an external magnet and reused for nine runs without any significant loss of catalytic activity.     

Copper(I) oxide nanoparticles supported on magnetic casein as a bio‐supported and magnetically recoverable catalyst for aqueous click chemistry synthesis of 1,4‐disubstituted 1,2,3‐triazoles

Copper(I) oxide nanoparticles supported on magnetic casein (Cu₂O/Casein@Fe₃O₄NPs) has been synthesized as a bio‐supported catalyst and was characterized using powder X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray and Fourier transform infrared spectroscopies, thermogravimetric analysis and inductively coupled plasma optical emission spectrometry. The catalytic activity of the synthesized catalyst was investigated in one‐pot three‐component reactions of alkyl halides, sodium azide and alkynes to prepare 1,4‐disubstituted 1,2,3‐triazoles with high yields in water. The reaction work‐up is simple and the catalyst can be magnetically separated from the reaction medium and reused in subsequent reactions.     

Copper Salt of 12‐Tungstophosphoric Acid: An Efficient and Reusable Heteropoly Acid for the Click Chemistry

Three components coupling of alkyl bromide, sodium azide and alkyne has been achieved using a catalytic amount of copper‐exchanged phosphotungstic acid (Cu‐TPA) in the presence of triethyl amine in DMF to afford substituted triazoles in good yields with high selectivity. Interestingly, the coupling of alkyl azide with alkyne proceeds readily at room temperature to furnish 1,2,3‐triazoles in excellent yields. The catalyst can be recovered and reused for three to four subsequent runs with a minimal decrease of activity. The use of copper modified heteropolyacids makes this procedure simple, convenient and environmentally friendly.     

Immobilization of copper ions onto α‐amidotriazole‐functionalized magnetic nanoparticles and their application in the synthesis of triazole derivatives in water

A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption and Fourier transform infrared spectroscopies, and thermogravimetric, elemental and energy‐dispersive X‐ray analyses. The results confirmed that a good level of organic groups was immobilized on the magnetic nanoparticles. Huisgen cycloaddition reaction was chosen as a model reaction for the investigation of catalyst activity under green conditions. Phenylacetylene and benzyl bromide derivatives were used for the synthesis of triazoles. The reaction proceeded with good to excellent yields for various alkynes and alkyl halides. To investigate catalyst activity for inactive alkynes, aliphatic alkynes were used in the model reaction. The corresponding triazoles were obtained in good to excellent yields and a high regioselectivity for products was obtained. The catalyst was easily separated using an external magnetic field and subsequently reused in ten reaction cycles without any loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Recyclable Porous Polymer‐Supported Copper Catalysts for Glaser and Huisgen 1,3‐Diolar Cycloaddition Reactions

A family of polymer‐attached phenanthrolines was prepared from solvothermal copolymerization of divinylbenzene with N‐(1,10‐phenanthroline‐5‐yl)acrylamide in different ratios. The polymer‐supported copper catalysts were obtained through typical impregnation with copper(II) salts. The polymers and supported copper catalysts have been characterized by N₂ adsortion, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TG); they exhibit a high surface area, hierarchical porosity, large pore volume, and high thermal and chemical stabilities. The copper catalyst has proved to be highly active for Glaser homocoupling of alkynes and Huisgen 1,3‐diolar cycloaddition of alkynes with benzyl azide under mild conditions at low catalyst loading. The heterogeneous copper catalyst is more active than commonly used homogeneous and nonporous polystyrene‐supported copper catalysts. In particular, the catalyst is easily recovered and can be recycled at least ten times without any obvious loss in catalytic activity. Metal leaching was prevented due to the strong binding ability of phenanthroline and products were not contaminated with copper, as determined by ICP analysis.     

Refinement of Copper(II) Azide with 1‐Alkyl‐5H‐tetrazoles: Adaptable Energetic Complexes

A concept for stabilizing highly sensitive and explosive copper(II) azide with 1‐N‐substituted tetrazoles is described. It was possible to stabilize the system by the use of highly endothermic, nitrogen‐rich ligands. The sensitivities of the resulting energetic copper coordination compounds can be tuned further by variation of the alkyl chain of the ligands and by phlegmatization of the complexes with classical additives during the synthesis. It is demonstrated, using the compound based on 1‐methyl‐5H‐tetrazole ([Cu(N₃)₂(MTZ)], 1 ) that this class of complexes can be applied as a potential replacement for both lead azide (LA) and lead styphnate (LS). The complex was extensively investigated according to its chemical (elemental analysis, single‐crystal and powder X‐ray diffraction, IR spectroscopy, scanning electron microscopy) and physico‐chemical properties (differential thermal analysis, sensitivities towards impact, friction, and electrostatic discharge) compared to pure copper(II) azide.     

Ligand‐free,copper‐catalyzed,one‐pot,three‐component synthesis of novel 1,2,3‐triazole‐linked indoles in magnetized water

Magnetized water (MW) is used as a green and new solvent‐promoting medium for the one‐pot, three‐component synthesis of novel 1,2,3‐triazole‐linked indoles catalyzed by copper iodide. A broad range of 2‐aryl‐1‐(prop‐2‐ynyl)‐1H‐indole‐3‐carbaldehydes were reacted with alkyl halides and sodium azide via copper‐catalyzed azide–alkyne cycloaddition reactions in MW in the absence of any ligand. This method offers the advantages of short reaction times, green procedure, low cost, simple work‐up, quantitative reaction yields, and no need for any organic solvent.     

Click approach to the three‐component synthesis of novel β‐hydroxy‐1,2,3‐triazoles catalysed by new (Cu/Cu2O) nanostructure as a ligand‐free,green and regioselective nanocatalyst in water

Copper nanostructures were produced as an effective and regioselective catalyst for the synthesis of 1,2,3‐triazoles from a wide range of raw materials, such as sodium azide, epoxides and terminal alkynes, in water via a one‐pot three‐component click reaction. The new heterogeneous catalyst was prepared by a simple ball mill reduction of CuO with NaBH₄ using a ball‐to‐powder weight ratio of 50:1 under air atmosphere at room temperature. The catalyst was fully characterized using scanning electron microscopy, energy‐dispersive X‐ray analysis, Fourier transform infrared spectroscopy and X‐ray diffraction. The copper nanostructures catalysed both ring opening and triazole cyclization steps. Products were obtained in high yields and short reaction times. The reactions were performed at ambient temperature in water as a green solvent. The Cu/Cu₂O nanostructures revealed high reusability and high stability via a simple recycling process.     

A new magnetic nanoparticle‐supported Schiff base complex of manganese: an efficient and recyclable catalyst for selective oxidation of alcohols

A new magnetic nanoparticle‐supported Schiff base complex of manganese was prepared via the copper‐catalyzed ‘click’ reaction of an aminosalicylidene manganese complex bearing terminal alkynyl with azide‐functionalized shell–core magnetic nanoparticles. The as‐prepared catalyst was applied in the oxidation of alcohols to corresponding aldehydes or ketones with high yield and selectivity when the reaction was carried out in dimethylsulfoxide at 110°C for 4 h using tert‐butyl hydroperoxide as oxidant. Moreover, the catalyst can be easily separated from the reaction mixture using an external magnet and reused five times with no significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

CuII‐Catalyzed Oxidative Formation of 5‐Alkynyltriazoles

In an alcoholic solvent under the catalysis of Cu(OAc)₂?H₂O, 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.     

Claycop/hydrazine: A new and highly efficient recyclable/reusable catalytic system for 1,4‐disubstituted‐1,2,3‐triazole synthesis under solvent‐free conditions

Clay‐supported copper(II) nitrate (claycop) has been used as an efficient catalyst for azide–alkyne cycloaddition reactions leading to 1,4‐disubstituted 1,2,3‐triazoles. The highly efficient claycop/hydrazine hydrate catalytic system affords triazoles in a few minutes (1–20 min) at room temperature, under mild and solvent‐free conditions. High regioselectivity, excellent yields, ease of claycop synthesis and recyclability/reusability of the catalyst are considered as practical merits of the protocol.     

Integration of CuAAC Polymerization and Controlled Radical Polymerization into Electron Transfer Mediated “Click‐Radical” Concurrent Polymerization

The successful chain‐growth copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) polymerization employing Cu(0)/pentamethyldiethylenetriamine (PMDETA) and alkyl halide as catalyst is first investigated by a combination of nuclear magnetic resonance, gel‐permeation chromatography, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. In addition, the electron transfer mediated “click‐radical” concurrent polymerization utilizing Cu(0)/PMDETA as catalyst is successfully employed to generate well‐defined copolymers, where controlled CuAAC polymerization of clickable ester monomer is progressed in the main chain acting as the polymer backbone, the controlled radical polymerization (CRP) of acrylic monomer is carried out in the side chain. Furthermore, it is found that there is strong collaborative effect and compatibility between CRP and CuAAC polymerization to improve the controllability.

     

Anchoring of Cu(II)–vanillin Schiff base complex on MCM‐41: A highly efficient and recyclable catalyst for synthesis of sulfides and 5‐substituted 1H–tetrazoles and oxidation of sulfides to sulfoxides

A copper(II)–vanillin complex was immobilized onto MCM‐41 nanostructure and was used as an inexpensive, non‐toxic and heterogeneous catalyst in the synthesis of symmetric aryl sulfides by the cross‐coupling of aromatic halides with S₈ as an effective sulfur source, in the oxidation of sulfides to sulfoxides using 30% H₂O₂ as a green oxidant and in the synthesis of 5‐substituted 1H –tetrazoles from a smooth (3 + 2) cycloaddition of organic nitriles with sodium azide (NaN₃). The products were obtained in good to excellent yields. This catalyst could be reused several times without loss of activity. Characterization of the catalyst was performed using Fourier transform infrared, energy‐dispersive X‐ray and atomic absorption spectroscopies, X‐ray diffraction, thermogravimetric analysis, and scanning and transmission electron microscopies.     

Sunlight‐Driven Copper‐Catalyst Activation Applied to Photolatent Click Chemistry

The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction of a copper(II)–DMEDA (N,N′‐dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.22 in MeOH, and a value approaching unity as determined in THF. The reduction process, which can also be conducted by irradiation at 365 nm by using a standard TLC (thin layer chromatography) lamp, is ascribed to a highly efficient photoinduced electron transfer (PET) process mediated by the benzophenone photosensitizer present in the carboxylate counterion. Having deaerated the reaction mixture, the photogenerated copper(I) species proved to be highly active for the CuAAC reaction, demonstrated by reactions conducted with low catalyst loading (0.5 mol %) on a range of clickable protected and non‐protected mono‐ and disaccharides. Once initiated, the reaction can be stopped at any time on introducing air into the reaction medium. Deoxygenation followed by irradiation restores the activity, making the copper(II)–DMEDA complex a switchable catalyst of practical value.     

A reusable polymer‐supported copper(I) catalyst for triazole click reaction on water: An experimental and computational study

In the search for establishing a clickable copper‐catalysed (3 + 2) Huisgen azide–alkyne cycloaddition (CuAAC) reaction under strict conditions, in particular in terms of preventing the presence of copper particles/traces in reaction products and using an environmentally benign medium such as water, we describe here the synthesis of an aminomethyl polystyrene‐supported copper(I) catalyst (Cu(I)‐AMPS) and its characterization by means of Fourier transform infrared and energy‐dispersive X‐ray spectroscopies and scanning electron microscopy. Cu(I)‐AMPS was found to be highly active in the CuAAC reaction of various organic azides with alkynes affording the corresponding 1,4‐disubstituted 1,2,3‐triazoles in a regioselective manner in air at room temperature and using water as solvent. The insolubility and/or partial solubility of the organic azide and alkyne precursors as well as the heterogeneous Cu(I)‐AMPS catalytic system points to the occurrence of the cycloaddition at the organic–water interface ‘on water’ affording quantitative yields of water‐insoluble 1,2,3‐triazoles. A mechanistic study was performed using density functional theory aiming at explaining the observed reactivity and selectivity of the Cu (I)‐AMPS catalyst in CuAAC reactions.     

Preparation and functionalization of linear and reductively degradable highly branched cyanoacrylate‐based polymers

Ethyl cyanoacrylate (ECA) was polymerized radically in the presence of small amounts of trifluoroacetic acid as effective inhibitor of incidental anionic polymerization. Methyl methacrylate and other functional vinyl monomers (e.g., 2‐chloroethyl and 2‐bromoethyl methacrylate) were copolymerized with ECA, yielding linear ECA‐rich copolymers, which could readily undergo further modifications, for instance nucleophilic substitution with azide. In the presence of a disulfide‐containing dimethacrylate crosslinker and a chain transfer agent (CBr₄) during the free radical copolymerizations of ECA with methacrylates, highly branched ECA‐based polymers containing disulfide groups at the branching points were obtained prior to gelation. The polymers degraded upon addition of reducing agents. The prepared polymers, which contained peripheral (chain end) alkyl bromide groups as well as pendant alkyl chloride or bromide groups were then reacted with sodium azide, affording azide‐containing polymers that were reacted with functional alkynes under copper‐catalyzed “click” chemistry conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3683–3693     

Click chemistry in materials synthesis. III. Metal‐adhesive polymers from Cu(I)‐catalyzed azide–alkyne cycloaddition

1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007     

Dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe3O4@SiO2 nanoparticles as a novel recyclable catalyst for N‐arylation of nitrogen heterocycles and green synthesis of 5‐substituted 1H‐tetrazoles

In this study, dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe₃O₄@SiO₂ nanoparticles were prepared via a multistep‐synthesis. Then, the synthesized composite was fully characterized by various techniques such as fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), dynamic light scattering (DLS), UV‐vis spectroscopy, energy dispersive X‐ray analysis (EDX), thermogravimetric analysis (TGA) and vibration sample magnetometer (VSM). From the information gained by FE‐SEM and TEM studies it can be inferred that the particles are mostly spherical in shape and have an average size of 50 nm. Also, the amount of Cu is determined to be 0.51 mmol/g in the catalyst by inductively coupled plasma (ICP) analyzer. This magnetic nano‐compound has been successfully applied as a highly efficient, magnetically recoverable and stable catalyst for N‐arylation of nitrogen heterocycles with aryl halides (I, Br) and arylboronic acids without using external ligands or additives. The catalyst was also employed in a one‐pot, three‐component reaction for the efficient and green synthesis of 5‐substituted 1H‐tetrazoles using various aldehydes, hydroxylamine hydrochloride and sodium azide in water. The magnetic catalyst can be easily separated by an external magnet bar and is recycled seven times without significant loss of its activity.