An approach to new chiral bicyclic imines and amines via Horner–Wadsworth–Emmons reaction

New chiral bicyclic imines, enamines and amines were prepared via Horner–Wadsworth–Emmons reaction of hexahydroquinoxalin-2(1H)-one-derived phosphonate, as the source of a phosphonate carbanion, and a wide range of structurally diverse carbonyl substrates. The simplicity of the synthetic protocol, high selectivity, and broad substrate scope are the main advantages of the presented methodology.

New chiral cyclic imines and enamines were prepared via HWE reaction, with selectivity dependent on the carbonyl substrate.     

A nanoscopic icosahedral {Mo72Fe30} cluster catalyzes the aerobic synthesis of benzimidazoles

In this study, the catalytic efficiency of amorphous {Mo₇₂Fe₃₀} nanocapsules as a safe Keplerate polyoxometalate in organic synthesis was exploited. The easy-made solid catalyst exhibited high efficiency using a very low dosage (0.02–0.05 mol%) in the catalyzed condensation of various aromatic 1,2-diamines and aldehydes for the aerobic synthesis of benzimidazoles with very small E-factor values (0.11–0.33). The superior catalytic activity of amorphous nanoclusters compared to that of its crystalline counterpart was demonstrated. The high activity and recyclability of heterogeneous catalysts in a green reaction media under oxygen atmosphere, make this environmentally benign organic process appropriate for our applied goals.

Catalytic activity of amorphous {Mo₇₂Fe₃₀} nanoclusters as a safe Keplerate polyoxometalate in aerobic synthesis of benzimidazoles was described.     

Facile synthesis of silver nanocatalyst decorated Fe3O4@PDA core–shell nanoparticles with enhanced catalytic properties and selectivity

In this work, we have successfully prepared core–shell nanoparticles (Fe₃O₄@PDA) wrapped with Ag using a simple and green synthesis method. Without an external reducing agent, silver nanoparticles (Ag NPs) with good dispersibility were directly reduced and deposited on a polydopamine (PDA) layer. Fe₃O₄@PDA@Ag showed excellent catalytic activity and recyclability for 4-nitrophenol, and also exhibited good catalytic selectivity for organic dyes (MO and MB). This simple and green synthesis method will provide a platform for other catalytic applications.

In this work, we have successfully prepared core–shell nanoparticles (Fe₃O₄@PDA) wrapped with Ag using a simple and green synthesis method.     

Metal- and oxidant-free electrochemically promoted oxidative coupling of amines

The selective oxidation of amines into imines is a priority research topic in organic synthesis and has attracted much attention over the past few decades. However, the oxidation of amines generally suffers from the drawback of transition-metal, even noble-metal catalysts. Thus, the strategy of metal- and oxidant-free selective synthesis of imines is highly desirable yet largely unmet. This paper unravels a metal-free and external oxidant-free electrochemical strategy for the oxidative coupling methodology of amines. This general transformation is compatible with various functional amines and led to functionalized imines in moderate to satisfactory yields.

This paper presents a metal-free and external oxidant-free electrochemical method for the oxidative coupling methodology of amines in moderate to satisfactory yields.     

Lithium bromide: an inexpensive and efficient catalyst for imine hydroboration with pinacolborane at room temperature

An efficient protocol for the hydroboration of imines is reported. Lithium halide salts are effective catalysts to convert aldimines and ketimines to their corresponding amines. Here, we report excellent isolated yield of secondary amines (>95%) using 3 mol% lithium bromide in THF at room temperature. In addition, DFT calculations for a plausible reaction pathway are reported.

An efficient protocol for the hydroboration of imines using LiBr is reported.     

Highly economical and direct amination of sp3 carbon using low-cost nickel pincer catalyst

Developing more efficient routes to achieve C–N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials. Over the past decade, improvements in catalyst design have moved synthesis away from expensive metals to newer inexpensive C–N cross-coupling approaches via direct amine alkylation. For the first time, we report the use of an amide-based nickel pincer catalyst (1) for direct alkylation of amines via activation of sp³ C–H bonds. The reaction was accomplished using a 0.2 mol% catalyst and no additional activating agents other than the base. Upon optimization, it was determined that the ideal reaction conditions involved solvent dimethyl sulfoxide at 110 °C for 3 h. The catalyst demonstrated excellent reactivity in the formation of various imines, intramolecularly cyclized amines, and substituted amines with a turnover number (TON) as high as 183. Depending on the base used for the reaction and the starting amines, the catalyst demonstrated high selectivity towards the product formation. The exploration into the mechanism and kinetics of the reaction pathway suggested the C–H activation as the rate-limiting step, with the reaction second-order overall, holding first-order behavior towards the catalyst and toluene substrate.

Developing more efficient routes to achieve efficient C–N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials.     

Direct synthesis of amides and imines by dehydrogenative homo or cross-coupling of amines and alcohols catalyzed by Cu-MOF

Oxidative dehydrogenative homo-coupling of amines to imines and cross-coupling of amines with alcohols to amides was achieved with high to moderate yields at room temperature in THF using Cu-MOF as an efficient and recyclable heterogeneous catalyst under mild conditions. Different primary benzyl amines and alcohols could be utilized for the synthesis of a wide variety of amides and imines. The Cu-MOF catalyst could be recycled and reused four times without loss of catalytic activity.

Oxidative dehydrogenative homo or cross-coupling of amines with alcohols to imines and amides was achieved with high to moderate yields at room temperature using Cu-MOF as an efficient and recyclable heterogeneous catalyst.     

A magnetically separable and recyclable g-C3N4/Fe3O4/porous ruthenium nanocatalyst for the photocatalytic degradation of water-soluble aromatic amines and azo dyes

Herein, we present the development of a visible-light-driven magnetically retrievable nanophotocatalyst made of porous ruthenium nanoparticles supported on magnetic carbon nitride (g-C₃N₄/Fe₃O₄/p-RuNP) for the facile removal/degradation of aromatic amines and azo dyes from wastewater. Aromatic amines and azo-based dyes in water bodies are highly toxic and carcinogenic even at very low concentrations and are difficult to separate because of their high solubility. Our nanocatalyst can efficiently degrade/decompose the aromatic amines and azo dyes under visible light (LED/sunlight) at room temperature and in a wide pH range (pH 5.0–9.0) without using any external chemicals. The magnetic property of the nanocatalyst facilitates its efficient and facile separation from the reaction mixture for reuse in multiple photocatalytic cycles. The nanocatalyst-based degradation of azo dyes and aromatic amines presented here is simple and convenient in terms of efficiency, energy, reusability and cost. The process also does not require any external chemicals and forms gaseous/less harmful end products.

A magnetically separable and recyclable g-C₃N₄/Fe₃O₄/porous ruthenium nanocatalyst display excellent photocatalytic degradation of water-soluble aromatic amines and azo dyes at ambient condition.     

Carboxylation of sodium arylsulfinates with CO2 over mesoporous K-Cu-20TiO2

A mesoporous ternary metal oxide (K-Cu-20TiO₂) from a simple sol–gel method was prepared to catalyze heterogeneously the carboxylation reaction of various sodium arylsulfinates under atmospheric carbon dioxide. The catalyst showed excellent selectivity and good functional group tolerance to carboxylation recycle. The oxidation state of active copper(i) by characterization using FTIR, XRD, TG, XPS and TEM techniques proved to be efficacious to conduct atom economical reactions.

A mesoporous ternary metal oxide (K-Cu-20TiO₂) from a simple sol–gel method was prepared to catalyze heterogeneously the carboxylation reaction of various sodium arylsulfinates under atmospheric carbon dioxide.     

Stereodivergent access to all four stereoisomers of chiral tetrahydrobenzo[f][1,4]oxazepines,through highly diastereoselective multicomponent Ugi–Joullié reaction

Starting from easily accessible chiral enantiopure 1,2-amino alcohols and salicylaldehydes, a concise route to cyclic imines has been developed. These chiral cyclic imines undergo a highly diastereoselective Ugi–Joullié reaction to give trans tetrahydrobenzo[f][1,4]oxazepines with the introduction of up to 4 diversity inputs. The cis isomer may also be attained, thanks to a thermodynamically controlled base catalysed epimerization. Free secondary amines have been obtained using an unprecedented “removable” carboxylic acid.

Starting from easily accessible enantiopure 1,2-aminoalcohols and salicylaldehydes, a concise and diastereodivergent route to tetrahydrobenzo[f][1,4]oxazepines has been developed.     

Conductivity and giant permittivity study of Zn0.5Ni0.5Fe2O4 spinel ferrite as a function of frequency and temperature

Ni_0.5Zn_0.5Fe₂O₄ was prepared by the solid state reaction route at different temperatures. The dielectric properties of spinel ferrites were investigated in the frequency range 50 Hz–10 MHz and in the temperature range 300–420 K. Conductance is shown to increase with increasing frequency and temperature. Impedance analyses indicated that the relaxation phenomenon is strongly dependent on temperature and frequency. The impedance plots displayed both intra- and inter-granular contributions. Electrical equivalent circuit was proposed to explain the impedance results. The decrease of giant permittivity values with the increase in frequency proves the dispersion in the low frequency range and is showing the Maxwell–Wagner interfacial polarization.

Ni_0.5Zn_0.5Fe₂O₄ was prepared by the solid state reaction route at different temperatures.     

A highly active worm-like PtMo nanowire for the selective synthesis of dibenzylamines

Worm-like nanowires are among the most active nanomaterials. In this study, we report the synthesis of dibenzylamine (DBA) motifs from reductive amination of either aldehydes or nitriles catalyzed by entirely new worm-like PtMo nanowires (PtMo WNWs). Under the assistance of H₂ gas, PtMo WNWs can be prepared in a facile manner, following which, their structure and composition are characterized by TEM, XRD, XPS, etc. Upon careful optimization of reaction parameters, the as-prepared PtMo WNWs work effectively in the activation of dihydrogen molecules, and both aldehydes and nitriles can be used as starting materials to fabricate DBAs under mild and green conditions. The reaction kinetics has been investigated, which reveals that the PtMo WNWs show superior activity in the conversion of imines into amines. This study provides a practical advancement in the preparation of amines. Moreover, the protocol reported herein is feasible for the synthesis of worm-like nanostructures with designed composition for various catalytic applications.

An efficient synthetic pathway of dibenzylamine (DBA) motifs from reductive amination of either aldehydes or nitriles catalyzed by highly active worm-like PtMo nanowires.     

Innovative application of magnetically modified bovine horn as a natural keratin resource in the role of value-added organocatalyst

This study presents the conversion of bovine horn powder (BHP) as an available and low-cost waste material to a value-added highly recyclable catalyst. This green catalyst was prepared through the immobilization of BHP, as a natural keratin resource, on the magnetic Fe₃O₄ nanoparticles. The successful preparation of the catalyst was fully investigated using Fourier transform infrared, X-ray diffraction, and energy-dispersive X-ray spectroscopies as well as field emission scanning electron microscopy, vibrating sample magnetometry, and thermogravimetry. The catalytic efficiency of the prepared magnetic organocatalyst was evaluated in the synthesis of a large series of amide derivatives through the solvent-free transamidation reaction of different amides and amines with yields of 75–96%.

The conversion of bovine horn powder as an available and low-cost waste material to a value-added recyclable organocatalyst for transamidation reaction.     

Tandem imine formation via auto-hydrogen transfer from alcohols to nitro compounds catalyzed by a nanomagnetically recyclable copper catalyst under solvent-free conditions

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst under solvent-free conditions. By this method, various imines were prepared in good to high yields from one-pot reaction of various alcohols (primary aromatic and aliphatic) and nitro compounds (aromatic and aliphatic) via an auto-hydrogen transfer reaction. Use of an inexpensive and easily reusable catalyst, without requiring any additives or excess amounts of benzyl alcohol as the reaction solvent are the other advantages of this method. This catalytic system has the merits of cost effectiveness, environmental benignity, excellent recyclability and good reproducibility.

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst.     

Robust,highly active,and stable supported Co(ii) nanoparticles on magnetic cellulose nanofiber-functionalized for the multi-component reactions of piperidines and alcohol oxidation

The new recyclable cobalt three-core magnetic catalyst obtained by anchoring a Schiff base ligand sector and cellulose nanofiber slings on MNP (Fe₃O₄) was prepared and named as MNP@CNF@ATSM–Co(ii). Separately, MNPs and CNF have adsorbent properties of great interest. In this way, this catalyst was designed to synthesize piperidine derivatives under solvent-free conditions and alcohol oxidation reactions in EtOH as the solvent. It should be noted that this catalyst is environmentally safe and does not need an external base. This MNPs@CNF@ATSM–Co(ii) separable catalyst has been evaluated using various characterization techniques such as FT-IR, XRD, FE-SEM, EDX, EDS, ICP, TGA, DLS, HRTEM, and VSM. The catalyst was compatible with a variety of benzyl alcohols, benzaldehydes, and amines derivatives, and gave complimentary coupling products with sufficient interest for all of them. The synergistic performance of Co (trinuclear) in the catalyst was demonstrated and its different homologs such as MNPs, MNPs@CNF, MNPs@CNF@ATS–Co(ii), and MNPs@CNF@ATSM–Co(ii) were separately synthesized and applied to a model reaction, and then their catalytic activity was investigated. Also, the performance of these components for the oxidation reaction of alcohols was evaluated. The advantages of the current protocol include the use of a sustainable and safe low temperature, eco-friendly solvent no additive, and long-term stability and magnetic recyclability of the catalyst for at least five successive runs, thus following green chemistry principles. This protocol is a benign and environment-friendly method for oxidation and heterocycle synthesis. This powerful super-magnetic catalyst can use its three arms to advance the reactions, displaying its power for multi-component reactions and oxidation.

The new recyclable cobalt three-core magnetic catalyst obtained by anchoring a Schiff base ligand sector and cellulose nanofiber slings on MNP (Fe₃O₄) was prepared and named as MNP@CNF@ATSM–Co(ii).     

One-pot synthesis of amides via the oxidative amidation of aldehydes and amines catalyzed by a copper-MOF

An efficient method for the oxidative amidation of aldehydes with primary aromatic and aliphatic amines has been developed for the synthesis of a wide variety of amides using inexpensive Cu₂(BDC)₂DABCO (Cu-metal–organic framework [MOF]) as a recyclable heterogeneous catalyst, and N-chlorosuccinimide and aqueous tert-butyl hydroperoxide as oxidants in acetonitrile. This amidation reaction is operationally straightforward and provides secondary amides in good yields in most cases, utilizing inexpensive and readily available reagents under mild conditions.

A method for oxidative amidation of aldehydes with primary amines was developed to synthesise a variety of amides using Cu₂(BDC)₂DABCO (Cu-MOF) as a recyclable heterogeneous catalyst, and N-chlorosuccinimide and aqueous tert-butyl hydroperoxide as oxidants in acetonitrile.     

Synthesis and evaluation of the SERS effect of Fe3O4–Ag Janus composite materials for separable,highly sensitive substrates

Fe₃O₄–Ag Janus composites were synthesized using a two-step solvothermal method. The optimal growth process was determined by investigating the relationship between the particle morphologies and reaction time. Magnetic and Raman spectroscopic measurements showed that the as-synthesized Janus composites have both good magnetic response and significant surface-enhanced Raman scattering (SERS) effects, as well as reproducibility. The calculated Raman enhancement factor reached an unprecedented magnitude of 10⁹ compared with the values of other Fe₃O₄–Ag compounds. Furthermore, the SERS effect was exhibited even at a concentration of probe molecules as low as 10⁻¹³ M. This demonstrates that the as-synthesized Fe₃O₄–Ag Janus composite particles have promise for application as separable, highly sensitive SERS substrates.

Fe₃O₄–Ag Janus composites were synthesized using a two-step solvothermal method.     

An efficient and recyclable nanocatalyst for the green and rapid synthesis of biologically active polysubstituted pyrroles and 1,2,4,5-tetrasubstituted imidazole derivatives

An effective process for the green and rapid synthesis of biologically active polysubstituted pyrroles and 1,2,4,5-tetrasubstituted imidazoles derivatives using Cu@imine/Fe₃O₄ MNPs catalyst under solvent-free conditions is explained. This catalyst showed high reactivity for the synthesis of a set of different derivatives of polysubstituted pyrroles and 1,2,4,5-tetrasubstituted imidazole derivatives under appropriate reaction conditions and short times. Moreover, the catalyst was also recycled and reused for six runs with no considerable reduction in reactivity and yields. Compared to the reported procedures, this method consistently demonstrates the advantages of low catalyst loading, short reaction times, easy separation and purification of the products, high yields, and high recoverability and recoverability of the catalyst.

So the use of Fe₃O₄@SiO₂–ZrCl₂-MNPs leads to an improved protocol in terms of the compatibility with the environment, yields of the products, reaction times and the amount of the catalyst when compared with other catalysts.     

Microflowers formed by complexation-driven self-assembly between palladium(ii) and bis-theophyllines: immortal catalyst for C–C cross-coupling reactions

The Pd catalyst for Suzuki–Miyaura or the other C–C coupling reactions is one of the central tools in organic synthesis related to medicine, agricultural chemicals and advanced materials. However, recycling palladium is a bottleneck for developing the extreme potential of Pd in chemistry. Herein, we established a new heterogeneous Pd catalytic system in which the catalyst is a nanopetal-gathered flower-like microsphere self-assembled from PdCl₂ and alkyl-linked bis-theophyllines. The microflowers catalyzed quantitatively the reaction of aryl bromides and phenylboronic acid in aqueous media at room temperature. It was found that the reaction proceeds better in an air atmosphere than in nitrogen gas even though the Pd(ii) species employed was lowered to 0.001 mol% in the substance. Very interestingly, the microflowers could be recycled 20 times without deactivation in the C–C coupling reaction between bromobenzene and phenylboronic acid in the presence of sodium chloride. We found that the sodium chloride added played an important role in maintaining the morphology of microflowers and preventing the formation of metallic Pd particles.

Bis-theophylline-palladium complex exhibit high catalytic activity in the C–C coupling reaction with excellent recyclability in the presence of NaCl.     

Hydroboration of nitriles and imines by highly active zinc dihydride catalysts

Eco-friendly zinc dihydrides stabilized by N-heterocyclic carbenes were demonstrated to be highly efficient catalysts for the double hydroboration of nitriles with pinacolborane, exhibiting turnover frequencies up to 3000 h⁻¹ at room temperature under solvent-free conditions. The reactions afforded corresponding diboronated amines with excellent yields and good functional group tolerance. A single Zn–H insertion product was isolated from a stoichiometric reaction of zinc dihydride with nitrile, and was proved to be an active species in this transformation. Kinetic studies were performed to give some insights into the catalytic reactions. In addition, zinc dihydride species also showed high activity for the hydroboration of imines to boronated amines.

Molecular zinc dihydrides were found to be highly efficient catalysts for the hydroboration of nitriles and imines at room temperature under solvent-free conditions.