Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.     

Catalytic oxidation of primary aromatic amines with sodium periodate catalyzed by Mn(III)salophen complex supported on polystyrene-bound imidazole

The catalytic activity of Mn(III)salophen complex supported on polystyrene-bound imidazole, [Mn(salophen)Cl-PSI], was studied in the oxidation of primary aromatic amines in acetonitrile/water, using sodium periodate as an oxygen source. Amines were oxidized efficiently to their corresponding azo derivatives in the presence of this catalyst. The heterogeneous catalyst showed high stability and reusability in the oxidation reactions and could be reused several times without loss of its activity. The effect of different solvents was studied in the oxidation of p-toluidine and CH₃CN/H₂O was chosen as the solvent.     

A novel method for the synthesis of 5-substituted 1H-tetrazole from oxime and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazoles from various oximes and sodium azide (NaN₃) by using copper acetate as a catalyst.     

AgNO3 catalyzed synthesis of 5-substituted-1H-tetrazole via [3+2] cycloaddition of nitriles and sodium azide

An efficient one-pot, convenient catalysis for the synthesis of 5-substituted-1H-tetrazoles is reported. The [3+2] cycloaddition involves various nitriles, sodium azide in refluxing DMF and AgNO₃ as catalyst to give corresponding 5-substituted-1H-tetrazoles in good to excellent yields. It is expected that the reaction proceeds via in situ formation of a silver azide species, which participates in coordination of nitrile moiety followed by cycloaddition of azide ion to give tetrazole.     

One-pot three-component synthesis of 1,4-disubstituted 1H-1,2,3-triazoles using green and recyclable cross-linked poly(4-vinylpyridine)-supported copper sulfate/sodium ascorbate in water/t-BuOH system

Cross-linked poly(4-vinylpyridine)-supported copper sulfate, [P₄-VP]CuSO4 as a green and recyclable, heterogeneous catalyst in the presence of sodium ascorbate (NaAsc), is reported for the regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles from benzyl halides, sodium azide and terminal alkyne in water/t-BuOH (1/1:V/V) at 70 °C. Various alkyl halides and benzyl halides, with electron-withdrawing groups as well as electron-donating groups, were used for synthesis of various 1,4-disubstituted-1,2,3-triazoles in high yields. The present procedure offers as short reaction time and simple reaction work up. This catalyst can be recovered by simple filtration and recycled several consecutive runs without any loss of its efficiency.     

A convergent synthesis of (17R,5Z,8Z,11Z,14Z)-17-hydroxyeicosa-5,8,11,14-tetraenoic acid analogues and their tritiated derivatives

17(R)-OH-AA and 14,15-dehydro-17(R)-OH-AA were synthesized from a common tetraacetylenic precursor and their azide derivatives were obtained in moderate yields via the corresponding p-toluenesulfonates. Since the azido group remained stable during tritiation procedure on Lindlar's catalyst in benzene, both 14,15-dehydro-17(S)-N₃-AA and 14,15-dehydro-17(R)-OH-AA constitute useful intermediates in the synthesis of radio-labelled 17(S)-N₃-AA and 17(R)-OH-AA. In contrast, reduction of azide in methanol afforded 17(S)-NH₂-AA with 95% yield.     

An efficient synthesis of 5-substituted 1H-tetrazoles via B(C6F5)3 catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazole derivatives from various nitriles and sodium azide (NaN₃) via [3+2] cycloaddition reaction using B(C₆F₅)₃ as a catalyst. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, low toxicity, easy work-up, high yields, and compatibility with other functional groups.     

CuFe2O4 nanoparticles: a magnetically recoverable and reusable catalyst for the synthesis of 5-substituted 1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted 1H-tetrazoles from various nitriles and sodium azide is described using magnetically recoverable and reusable CuFe₂O₄ nanoparticles. A wide variety of aryl nitriles underwent [2+3] cycloaddition under mild reaction conditions to afford tetrazoles in good to excellent yields. The catalyst was magnetically separated and reused five times without significant loss of catalytic activity.     

[Mn(TPPS)] immobilized on ionic liquid-modified silica as a heterogeneous and reusable catalyst for epoxidation of alkenes with NaIO<Subscript>4</Subscript> under ultrasonic irradiation

Effective epoxidation of alkenes using sodium periodate was accomplished with Manganese (III) tetrakis(p-sulfonatophenyl)porphyrin, [C₄₄H₂₆N₄O₁₂S₄Na₄], supported on ionic liquids-modified silica, Im-SiO₂, under ultrasonic irradiation conditions is reported. This heterogeneous catalyst, [Mn(TPPS)@SiO₂-Im] was characterized by elemental analysis, scanning electron microscopy (SEM), FT-IR and UV–Vis spectroscopic methods. The synthesized hybrid catalyst was applied for efficient epoxidation of various alkenes with sodium periodate in acetonitrile under ultrasonic irradiation conditions. This solid catalyst can be easily recovered by simple filtration and reused several time without apparent loss of its catalytic activity.     

Synthesis of azido-polymers of butadiene

Iodine azide adds to cyclohexene in acetonitrile or 4:1 methylene chloride/acetonitrile to give trans-1-azido-2-iodocyclohexane. In methylene chloride this reaction gives a mixture of the cis-and trans-iodoazides owing to competing radical addition. Iodine azide adds to 1-hexene in acetonitrile by an ionic mechanism to give a 3:1 mixture of the 2-azido-1-azido- and 1-azido-2-iodohexanes. Dehydroiodination of the model iodoazides proceeds smoothly with potassium t-butoxide in diethyl ether or THF in the presence of 5 mol % 18-crown-6 at room temperature, giving in the previous example a mixture of 2-azido- and trans-1-azidohexenes. Polybutadiene, carboxyterminated poly(acrylonitrile-co-butadiene), and hydroxy-terminated polybutadiene gave iodoazide derivatives with up to 96% of the theoretical maximum nitrogen content and strong azide IR absorption. High azidoiodination gave polymer with N₃/I ratios slightly higher than unity while low percent azidoiodination led to polymer with N₃/I ratios of as low as 2:3. All of the nitrogen introduced was in the form of azide function. Dehydroiodination gave polymers with vinyl azide functionality and caused loss of some of the azide groups. All the azidoiodinated polymers decomposed between 120 and 160°C. The dehydroiodinated materials were less stable, decomposing between 100 and 150°C. The temperature of initial decomposition decreased as azide content increased. Polymers with >55–60% of the theoretical maximum azide content were shock sensitive.     

KIT-6-anchored sulfonic acid groups as a heterogeneous solid acid catalyst for the synthesis of aryl tetrazoles

In the current study, a simple, environmentally benign and cost-effective method is presented for the preparation of 5-substituted-1H-aryltetrazoles. To this goal, mesoporous KIT-6 silica anchored with sulfonic acid (–SO₃H) groups via post-grafting modification was synthesized using the sol–gel method and characterized by XRD, TGA, FTIR, BET, TEM and SEM techniques. For the preparation of tetrazole derivatives, the effect of various parameters such as catalyst amount, aryl nitrile:azide ratio, temperature and reaction time was tested. The hybrid organic/inorganic catalyst could be recovered easily through a simple filtration and reused multiple times without significant loss in activity.     

Silica supported lanthanum triflate mediated synthesis of 5-substituted-1H tetrazoles

Silica supported lanthanum triflate (Ln(OTf)₃-SiO₂) promoted synthesis of 5-substituted 1H-tetrazoles via [3+2] cycloaddition between aromatic/heteroaromatic nitriles and sodium azide is a high product yielding, facile, and straightforward procedure. Non toxicity, recovery, and reusability for three continuous cycles are the noteworthy features of the currently employed heterogeneous catalyst.     

Magnetically recoverable copper ferrite catalyzed cascade synthesis of 4-Aryl-1H-1,2,3-triazoles under microwave irradiation

Magnetically active CuFe₂O₄ catalyzed cascade synthesis of 4-Aryl-1H-1,2,3-triazoles under microwave irradiation starting from aromatic aldehydes, sodium azide and nitromethane has been developed and demonstrated here. The catalyst system needed for the purpose was prepared following a procedure by A. Dandiya et al. with a slight modification and was characterized using FT-IR, XRD, SEM-EDX and TEM analysis. The most notable advantage of the developed methodology is the excellent time economy to carry out the transformation. Other features include simple operating procedure, wide substrate coverage and easy recovery of the catalyst. Reusability of the catalyst has been tested and found to be very satisfactory up to sixth cycle without significant loss in efficiency. All the synthesized compounds have been characterized using FTIR, ¹H & ¹³CNMR spectroscopy, HRMS.     

Catalyst-free synthesis of N-rich heterocycles via multi-component reactions

Efficient and straightforward methods for the synthesis of 5-substituted 1H-tetrazoles via multi-component reaction of α-dicarbonyl compounds, 2,3-diaminomaleonitrile and sodium azide without any catalyst has been reported. These general protocols provide a wide variety of N-rich heterocyclic compounds (1H-tetrazole-5-yl) pyrazines and di(1H-tetrazole-5-yl) pyrazines, in good to excellent yields.     

Living cationic polymerization of an azide‐containing vinyl ether toward addressable functionalization of polymers

We first achieved the living cationic polymerization of azide‐containing monomer, 2‐azidoethyl vinyl ether (AzVE), with SnCl₄ as a catalyst (activator) in conjunction with the HCl adduct of a vinyl ether [H‐CH₂CH(OR)‐Cl; R ? CH₂CH₂Cl, CH₂CH(CH₃)₂]. Despite the potentially poisoning azide group, the produced polymers possessed controlled molecular weights and fairly narrow distributions (M_w/M_n ～ 1.2) and gave block polymers with 2‐chloroethyl vinyl ether. The pendent azide groups are easily converted into various functional groups via mild and selective reactions, such as the Staudinger reduction and copper‐catalyzed azide‐alkyne 1,3‐cycloaddition (CuAAC; a “click” reaction). These reactions led to quantitative pendent functionalization into primary amine (? NH₂), hydroxy (? OH), and carboxyl (? COOH) groups, at room temperature and without any acidic or basic treatment. Thus, poly(AzVE) is a versatile precursor for a wide variety of functional vinyl ether polymers with well‐defined structures and molecular weights. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1449–1455, 2010     

Kinetisch-katalytische Bestimmungen in einem zweiphasensystem unter verwendung eines fallrohres

A rather simple method for kinetic-catalytic determinations is described, in which the reactants are dissolved in two immiscible liquid phases. Drops of the heavier phase fall through the lighter one contained in a vertical glass tube. As the drops fall, the reactants come into contact with each other at the interface, thus causing a change in the drops. The length of fall needed for completion of reaction is a measure of the concentration of the catalyst (e.g., decolorization of the drops in the determination of copper by the reaction between iron(III) and thiosulphate). If a gaseous reaction product is formed (e.g., N₂ or O₂) and adsorbed on the falling drop, then the drop stops falling and rises again. The depth of fall or the time needed for the drop to return to the upper end of the tube can be used as a measure for the concentration of catalyst (e.g., determination of thiosulphate with the iodine/azide reaction, or of copper as catalyst for the decomposition of hydrogen peroxide).     

CS@Cu2O and magnetic Fe3O4@SiO2-pAMBA-CS-Cu2O as heterogeneous catalysts for CuAAC click reaction

The recovery of agricultural and food wastes are one of the main areas of current research for optimal biowaste management to reduce greenhouse gas (GHG) emissions that are generated when it is not properly treated. Corn silk (CS) as biowaste from the agricultural sector is a rich source of natural compounds especially polysaccharides. We present here a chemical activation method to convert CS to values added heterogeneous catalyst for the synthesis of triazoles compounds via copper catalyzed azide–alkyne cycloaddition (CuAAC) reaction. For this purpose, cuprous oxide coated CS (CS@Cu₂O) and multifunctional Fe₃O₄@SiO₂–para-aminomethyl benzoic acid–CS–Cu₂O composite (denoted as Fe₃O₄@SiO₂‐pAMBA-CS‐Cu₂O) were fabricated. Different analytical techniques have been used to describe the size, crystal structure, elemental composition and other physical properties of the fabricated catalysts. These heterogeneous catalysts showed excellent catalytic activities for the synthesis of 1,4-disubstituted-1,2,3-triazoles via click reaction in H₂O at 70 °C under base and external-reductant-free conditions. The magnetic properties of the catalyst allowed easy separation after reaction by simply applying an external magnet. Other advantages of this work are the recyclability of the catalyst, the absence of reducing agent and base, besides utilisation of bio wastes for the production of heterogeneous catalyst.     

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.     

Organocatalyzed regio- and stereoselective diamination of functionalized alkenes

The first organocatalyzed diamination reaction of alkenes with N,N-dichlorotoluenesulfonamide (TsNCl₂) and acetonitrile as nitrogen sources was reported. The catalytic diamination reaction was convenient to carry out, resulting in imidazoline products with good yields and excellent regio- and stereoselectivities. Several other organic molecules were also tried as catalyst for this reaction and good results were achieved. A new one-pot synthesis of vicinal diamines via the current PPh₃-catalyzed diamination and the hydrolysis of resulting imidazoline products with SnCl₄ as promoter was also established.     

Nano TiO2/SO4 as a heterogeneous solid acid catalyst for the synthesis of 5-substited-1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted-1H-tetrazoles from various nitriles and sodium azide is reported using nano TiO₂/SO₄²⁻ as an effective heterogeneous catalyst. A wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in good to excellent yields.