Three-Component Coupling of Aldehydes, Amines, and Alkynes Catalyzed by Oxidized Copper Nanoparticles on Titania

Synthesis of propargylamine: pioneering a green path with non-conventional KA2 coupling approach

The KA2 coupling reaction is a well-explored and versatile method for forming C-C bonds in synthetic chemistry. It is composed of ketone, amine, and alkyne, which play a major role in the synthesis of propargylamines, known for their diverse biological activities and are used in treating neurogenetical disorders. The KA2 coupling is highly challenging due to the low reactivity of ketimines toward nucleophilic attacks with metal acetylide intermediates formed by activating the C-H bond of the alkyne. Despite predominant studies conducted on thermal conditions for KA2 coupling reactions, green and sustainable approaches like non-conventional methods still have a lot to achieve. This review article provides a comprehensive introduction to the non-conventional approach in the KA2 coupling reaction, outlining its mechanisms and exploring future aspects.

Stabilization of copper nanoparticles onto the double Schiff-base-functionalized ZSM-5 for A3 coupling reaction catalysis aimed under mild conditions

In this research a highly efficient and heterogeneous catalyst of ZSM-5@APTMS@(E)-4-((pyridin-2-ylimino)methyl) benzaldehyde@Cu-NPs was synthesized for upgrading the A³ coupling reaction for the synthesis of propargylamines under mild conditions. Rational tuning of the microenvironment of metallic NPs to improve efficiency and reusability in catalytic performances is of significance for scalable applications. Firstly, ZSM-5 was immobilized with APTMS (3-aminopropyltrimethoxysilane) and further modified with (E)-4-((pyridin-2-ylimino)methyl)benzaldehyde. Subsequently, the amine-activated zeolite@(E)-4-((pyridin-2-ylimino)methyl)benzaldehyde was applied to increase the stabilization of Cu metal nanoparticles. The catalyst was treated with hydrazine to reduce Cu(ii) to Cu(0), which led to active metal sites. The results of catalytic performance in comparison with different parts of catalysis indicate high efficiency due to the stabilization of copper nanoparticles onto the newly synthesized support of MOF modified with nitrogen aromatic groups. The addition of N-rich organic ligand through modification alters the electronic structure of the final composite in favor of the progress of the A³-coupling reaction. Moreover, the proposed catalyst showed no reduction in the catalytic performance up to four cycles, and a minor loss of efficiency occurs after the seventh cycle. In addition, the catalyst was effectively recycled up to 7 times without leaching of Cu-NPs.

N-Heterocyclic Carbene Silver Complex Modified Polyacrylonitrile Fiber/MIL-101(Cr) Composite as Efficient Chiral Catalyst for Three-Component Coupling Reaction

Complex asymmetric synthesis can be realized by the chiral induction of amino acids in nature. It is of great significance to design a new biomimetic catalytic system for asymmetric synthesis. In this context, we report the preparation and characterization of the composite of polyacrylonitrile fiber (PANF) and metal-organic framework to catalyze the chiral synthesis of propargylamines. A confined microenvironment is established with N-heterocyclic carbene (NHC) silver complex-supported PANF and D-proline-encapsulated MIL-101(Cr). This novel supported catalyst demonstrated high activity in addition to excellent stereoselectivity in the three-component reaction between alkynes, aldehydes, and amines (A3). The regeneration can be realized by adsorption of D-proline again when the stereoselectivity decreases after recycle uses. By regulating the confined microenvironment on the composite, the activity and selectivity of the catalytic system are improved with turnover numbers of up to 2800 and 98% ee. The biomimetic catalytic system to A3 coupling reaction is systematically studied, and the synergistic catalytic mechanism between NHC-Ag and D-proline in the confined microenvironment is revealed.

Supported metals on porous solids as heterogeneous catalysts for the synthesis of propargylamines

This perspective summarizes recent developments in the synthesis of propargylamines using porous solids (zeolites, MOFs and carbon) as supports/catalysts.

Copper nanocatalysts applied in coupling reactions: a mechanistic insight

Copper-based nanocatalysts have seen great interest for use in synthetic applications since the early 20th century, as evidenced by the exponential number of contributions reported (since 2000, more than 48 000 works published out of about 81 300 since 1900; results from SciFinder using "copper nanocatalysts in organic synthesis" as keywords). These huge efforts are mainly based on two key aspects: (i) copper is an Earth-abundant metal with low toxicity, leading to inexpensive and eco-friendly catalytic materials; and (ii) copper can stabilize different oxidation states (0 to +3) for molecular and nanoparticle-based systems, which promotes different types of metal-reagent interactions. This chemical versatility allows different pathways, involving radical or ionic copper-based intermediates. Thus, copper-based nanoparticles have become convenient catalysts, in particular for couplings (both homo- and hetero-couplings), transformations that are involved in a remarkable number of processes affording organic compounds, which find interest in different fields (medicinal chemistry, natural products, drugs, materials, etc.). Clearly, this richness in reactivity makes understanding the mechanisms more complex. The present review focuses on the analysis of reported contributions using monometallic copper-based nanoparticles as catalytic precursors applied in coupling reactions, paying attention to those shedding light on the reaction mechanism.

Ultra-fast Cu-based A3-coupling catalysts: faceted Cu2O microcrystals as efficient catalyst-delivery systems in batch and flow conditions

Cu(I) catalysts were studied for the synthesis of a propargylamine via A3-coupling of aldehyde, amine, and alkyne, under solvent-free and low loading conditions, using batch microwave or flow thermal heating. We explored ultra-low loading conditions with Cu(I) salts as fast and active catalysts featuring turnover frequencies (TOFs) above 105 h−1. Well-defined octahedral and cubic Cu2O microcrystals were also successfully applied and compared with this reaction. Both types of microcrystals exhibited excellent catalytic activities within minutes, via in situ generation of low dose of Cu(I) ions within the reaction medium, to achieve TON beyond 2000 and recycling up to 10 times in a flow reactor. The study of the catalytic system demonstrated that the activity was surface-structure dependent and allowed for the design of low Cu contamination A3-coupling systems, affording a product at the decigram scale, with Cu contamination below FDA recommendations for drug synthesis, without the need for a purification procedure.

Silver incorporated into g-C3N4/Alginate as an efficient and heterogeneous catalyst for promoting click and A3 and KA2 coupling reaction

Fe3O4/g-C3N4/Alginate-Ag nanocomposite as a novel and effective nanocatalyst was successfully prepared. This nanocomposite was fully characterized using several techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy with energy dispersive spectroscopy (FESEM-EDS), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). In addition, the catalytic activity of this novel and characterized nanocatalyst was investigated in the regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles via click reaction and A3 and KA2 coupling reaction in aqueous media. The prepared nanocatalyst was simply recovered by using an external magnet and reused for several times with a slight loss of catalytic activity.

Solvent-free synthesis of propargylamines: an overview

Propargylamines are a class of compounds with many pharmaceutical and biological properties. A green approach to synthesize such compounds is very relevant. This review aims to describe the solvent-free synthetic approaches towards propargylamines via A3 and KA2 coupling reactions covering the literature up to 2021.

Cu/SiO2-Pr-NH-Benz as a novel nanocatalyst for the efficient synthesis of 1,4-disubstituted triazoles and propargyl amine derivatives in an aqueous solution

In this work, an innovative nanocatalyst (Cu/SiO₂-Pr-NH-Benz) was synthesized and applied to coupling and click reaction in an aqueous solution. This work reports an efficient and straightforward approach for synthesizing diverse propargylamine and 1,2,3-triazole derivatives in excellent yield and short-time reaction. Also, a novel method involving the Cu NPs supported on the SiO₂ nanocatalyst as a heterogeneous novel catalyst for the “one-pot” three-component A³-coupling of aldehyde, amine, and alkynes and “one-pot” click reaction between alkyne, benzyl halide, and sodium azide in the water at room temperature was developed. Significant advantageous such as enhanced catalytic activity with efficient recycling for the one-pot synthesis of 1,4-disubstituted triazoles and propargyl amine derivatives and in green condition were observed. Also, after five successive reactions, the catalytic activity of recycled Cu/SiO₂-Pr-NH-Benz remained high without significant loss in its intrinsic activity.

Crystal structure of tert-butyl 4-[4-(4-fluoro-phen-yl)-2-methyl-but-3-yn-2-yl]piperazine-1-carboxyl-ate

The title sterically congested piperazine derivative, C20H27FN2O2, was prepared using a modified Bruylants approach. A search of the Cambridge Structural Database identified 51 compounds possessing an N-tert-butyl piperazine substructure. Of these only 14 were asymmetrically substituted on the piperazine ring and none with a synthetically useful second nitro-gen. Given the novel chemistry generating a pharmacologically useful core, determination of the crystal structure for this compound was necessary. The piperazine ring is present in a chair conformation with di-equatorial substitution. Of the two N atoms, one is sp 3 hybridized while the other is sp 2 hybridized. Inter-molecular inter-actions resulting from the crystal packing patterns were investigated using Hirshfeld surface analysis and fingerprint analysis. Directional weak hydrogen-bond-like inter-actions (C-H⋯O) and C-H⋯π inter-actions with the dispersion inter-actions as the major source of attraction are present in the crystal packing.

A review on multicomponent reactions catalysed by zero-dimensional/one-dimensional titanium dioxide (TiO2) nanomaterials: Promising green methodologies in organic chemistry

Heterogeneous catalysis has currently become an emerging tool for the design and development of sustainable manufacturing processes in order to obtain advanced intermediates, fine chemicals, and bioactive molecules. This field has been considered efficient and eco-friendly, as it investigates the utilization of non-hazardous metals for atom-economical reactions. Nanomaterials have created a significant impact on scientific and engineering advancements due to their tunable properties with superior performance over their massive counterparts. Due to the increased demand for heterogeneous catalysts in industries and academia, different transition metal oxides have been made into substantial nanostructures. Among them, titanium dioxide (TiO₂) nanomaterials have received more attention on account of their chemical stability, low cost, dual acid-base properties, good oxidation rate and refractive index. Different modifications of TiO₂ extend their applications as active catalysts or catalyst supports in diverse catalytic processes, such as photovoltaics, lithium batteries, pigments and others. One-dimensional (1-D) TiO₂ nanostructures such as nanotubes, nanowires and nanorods have achieved greater importance owing to the unique properties of improved porosity, decreased inter-crystalline contacts, large surface-to-volume ratio, superior dispersibility, amplified accessibility of hydroxyl (-OH) groups and presence of good concentrations of Brønsted/Lewis acid sites. Since the discovery, 1-D TiO₂ nanostructures have served good photocatalytic applications, but were less explored in organic transformations. While many articles and reviews have covered the applications of 0-D and 1-D TiO₂ nanostructured materials (NSMs) in photoelectrochemical reactions and solar cells, there are other interesting applications of these as well. In contrast to the conventional multi-step processes that utilise the stepwise formation of individual bonds, one-pot conversions based on multicomponent reactions (MCRs) have acquired much significance in contemporary organic synthesis. This paper presents a critical review on history, classification, design and synthetic utility of titania-based nanostructures, which could be used as robust solid-acid catalysts and catalyst supports for MCRs. Further, to put ideas into perspective, the introduction and applications of MCRs for various organic transformations have been discussed.

Magnetic AgNPs/Fe3O4@chitosan/PVA nanocatalyst for fast one-pot green synthesis of propargylamine and triazole derivatives

A new green magnetic nanocatalyst was introduced for one-pot fast synthesis of propargylamine and triazole derivatives.

A core–shell superparamagnetic metal–organic framework: a recyclable and green catalyst for the synthesis of propargylamines

This is the first report on the use of a magnetic metal–organic framework for the green synthesis of propargylamine derivatives.

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

Gold nanoparticles stabilized by PEG-tagged imidazolium salts as recyclable catalysts for the synthesis of propargylamines and the cycloisomerization of γ-alkynoic acids

Water-soluble gold nanoparticles prepared in the presence of PEG-tagged tris-imidazolium bromide, containing Au(0) and Au(i) species, are reusable catalysts.

Synthesis of polyhydroquinolines and propargylamines through one-pot multicomponent reactions using an acidic ionic liquid immobilized onto magnetic Fe3O4 as an efficient heterogeneous catalyst under solvent-free sonication

A nano-sized Fe₃O₄-supported Lewis acid ionic liquid catalyst for the synthesis of polyhydroquinolines and propargylamines under ultrasound irradiation has been developed. LAIL@MNP was synthesized from imidazolium chlorozincate(ii) ionic liquid grafted onto the surface of Fe₃O₄ nanoparticles and evaluated by FT-IR, TGA, SEM, Raman, TEM, ICP-OES, and EDS. The multicomponent synthesis of polyhydroquinolines and propargylamines proceeded smoothly to afford the desired products in high yields. LAIL@MNP can be separated easily from the reaction mixture and reused for several runs without a significant degradation in catalytic activity.

A nano-sized Fe₃O₄-supported Lewis acid ionic liquid catalyst for the synthesis of polyhydroquinolines and propargylamines under ultrasound irradiation has been developed.

Synthesis of Propargylamines via Michael Addition Using Methyl Vinyl Ketone Derivatives, 1-Alkynes, and Secondary Amines Catalyzed by Copper (I) Halides

Propargylamines are synthesized from methyl vinyl ketone derivatives, 1-alkynes, and secondary amines catalyzed by Cu salts involving the Michael addition of amine followed by an unusual C-C bond cleavage and addition of metal acetylides formed in situ to iminium ions. In this approach, the di-, tri-, and tetrasubstituted propargylamines are synthesized in 46-98% yields.

ZnCl2 loaded TiO2 nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines

One-pot green synthesis of propargylamines using ZnCl₂ loaded TiO₂ nanomaterial under solvent-free conditions has been effectively accomplished. The aromatic aldehydes, amines, and phenylacetylene were reacted at 100 °C in the presence of the resultant catalyst to form propargylamines. The nanocrystalline TiO₂ was initially synthesized by a sol-gel method from titanium(iv) isopropoxide (TTIP) and further subjected to ZnCl₂ loading by a wet impregnation method. X-ray diffraction (XRD) patterns revealed the formation of crystalline anatase phase TiO₂. Field emission scanning electron microscopy (FESEM) showed the formation of agglomerated spheroid shaped particles having a size in the range of 25-45 nm. Transmission electron microscopy (TEM) validates cubical faceted and nanospheroid-like morphological features with clear faceted edges for the pure TiO₂ sample. Surface loading of ZnCl₂ on spheroid TiO₂ nanoparticles is evident in the case of the ZnCl₂ loaded TiO₂ sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti⁴⁺ and Zn²⁺ species in the ZnCl₂ loaded TiO₂ catalyst. Energy-dispersive X-ray (EDS) spectroscopy also confirmed the existence of Ti, O, Zn and Cl elements in the nanostructured catalyst. 15% ZnCl₂ loaded TiO₂ afforded the highest 97% yield for 3-(1-morpholino-3-phenylprop-2-ynyl)phenol, 2-(1-morpholino-3-phenylprop-2-ynyl)phenol and 4-(1,3-diphenylprop-2-ynyl)morpholine under solvent-free and aerobic conditions. The proposed nanostructure-based heterogeneous catalytic reaction protocol is sustainable, environment-friendly and offers economic viability in terms of recyclability of the catalyst.

Zn-Catalyzed Multicomponent KA2 Coupling: One-Pot Assembly of Propargylamines Bearing Tetrasubstituted Carbon Centers

Tetrasubstituted propargylamines comprise a unique class of highly useful compounds, which can be accessed through the multicomponent coupling between ketones, amines, and alkynes (KA² coupling), an underexplored transformation. Herein, the development of a novel, highly efficient, and user-friendly catalytic system for the KA² coupling, based on the environmentally benign, inexpensive, and readily available zinc acetate, is described. This system is employed in the multicomponent assembly of unprecedented, tetrasubstituted propargylamines derived from structurally diverse, challenging, and even biorelevant substrates. Notable features of this protocol include the demonstration of the enhancing effect that neat conditions can have on catalytic activity, as well as the expedient functionalization of hindered, prochiral cyclohexanones, linear ketones, and interesting molecular scaffolds such as norcamphor and nornicotine.