Synthesis and Reactivity of Propargylamines in Organic Chemistry

Yolk-Shell Au NPs@Carbon Porous Nanoreactors Derived from ZIF-8: A High-Efficiency Catalyst for Three-Component Coupling Reaction

A yolk-shell Au NPs@carbon porous nanoreactor with an active gold (Au) core and a porous carbon shell has been fabricated and demonstrates excellent high activity and cyclic stability as a heterogeneous catalyst for the three-component coupling reaction of aldehyde, amine, and alkyne. Remarkably, the unique yolk-shell nanostructure can protect gold nanoparticles (Au NPs) from aggregation, allow for efficient mass transport, and benefit substrate enrichment, giving rise to enhanced activity, stability, and recyclability.

Regioselective 1,4-/1,3-Difunctionalization of 1,3-Enynes with Selenosulfonates in Water

1,4-/1,3-Regioselective bifunctionalization of 1,3-enynes with selenosulfonates in water under catalyst-free conditions for the construction of sulfonyl allene and 1,3-disulfonyl-conjugated dienes respectively have been developed. The reactions feature mild reaction conditions in aqueous solution and remarkable regioselectivity controlled by substrates.

Isocyanide-Based Multicomponent Reactions Coupled One-Pot Process: Efficient Tools to Diversity-Oriented Synthesis of Structural Peptidomimetics

Multicomponent diversity-oriented synthesis (DOS) of conformationally anchored structural peptidomimetics like 2,5-diketopiperazines (2,5-DKP) containing heterocyclic bioisosteres of the amide bond, such as 1,2,3-triazoles and 1,5-disubstituted tetrazoles (1,5-DS-T) is described. Structural peptidomimetics are synthesized from similar available starting materials, via a strategy based on isocyanide-based multicomponent reactions (IMCRs): Ugi-4CR and Ugi-Azide (UA), followed by a one-pot process: SN2/intramolecular alkyne-azide cycloaddition (IAAC). The sequential aligning of two powerful synthetic tools (IMCR and IAAC) has parallelly contributed to generate anchored conformation and complexity in target molecules, which are considered structural peptidomimetics of 2,5-DKP. Herein, the 1,2,3-triazole ring plays a key role in the preference for the boat conformation. Furthermore, the use of UA reaction generates scaffold diversity at the N-1 α-carbon of the pyrazinone ring, replacing a linear amide bond with a heterocyclic bioisostere such as 1,5-DS-T leading to the synthesis of novel tricyclic peptidomimetics. The DFT calculations confirmed the boat conformation of the synthesized molecules.

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.

Consecutive π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition promoted by in situ generated 2-benzopyrylium as the photoredox catalyst

A π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition sequence was developed, which utilises in situ generated 2-benzopyrylium cation intermediates as photoredox catalysts and electrophilic substrates to form 1H-isochromene derivatives in good yields in most cases. The key 2-benzopyrylium intermediates were generated through the activation of the alkyne moiety of ortho-carbonyl alkynylbenzene derivatives by such π-Lewis acidic metal catalysts as AgNTf2 and Cu(NTf2)2, and the subsequent intramolecular cyclisation and proto-demetalation using trifluoroacetic acid. Further photo-excitation of the 2-benzopyrylium intermediates facilitated single-electron transfer from a benzyltrimethylsilane derivative as a donor molecule to promote the radical addition of arylmethyl radicals to the 2-benzopyrylium intermediates.

The untold story of starch as a catalyst for organic reactions

Starch is one of the members of the polysaccharide family. This biopolymer has shown many potential applications in different fields such as catalytic reactions, water treatment, packaging, and food industries. In recent years, using starch as a catalyst has attracted much attention. From a catalytic point of view, starch can be used in organic chemistry reactions as a catalyst or catalyst support. Reports show that as a catalyst, simple starch can promote many heterocyclic compound reactions. On the other hand, functionalized starch is not only capable of advancing the synthesis of heterocycles but also is a good candidate catalyst for other reactions including oxidation and coupling reactions. This review tries to provide a fair survey of published organic reactions which include using starch as a catalyst or a part of the main catalyst. Therefore, the other types of starch applications are not the subject of this review.

Enantioselective and Regiodivergent Synthesis of Propargyl- and Allenylsilanes through Catalytic Propargylic C-H Deprotonation

We report a highly enantioselective intermolecular C-H bond silylation catalyzed by a phosphoramidite-ligated iridium catalyst. Under reagent-controlled protocols, propargylsilanes resulting from C(sp3)-H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less-hindered site was also observed. A variety of electrophilic silyl sources (R3SiOTf and R3SiNTf2), either commercial or in situ-generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, 1,3-enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η3-propargyl/allenyl Ir intermediate is generated upon π-complexation-assisted deprotonation and undergoes outer-sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step.

Copper-Catalyzed Enantioconvergent Radical N-Alkylation of Diverse (Hetero)aromatic Amines

The 3d transition metal-catalyzed enantioconvergent radical cross-coupling provides a powerful tool for chiral molecule synthesis. In the classic mechanism, the bond formation relies on the interaction between nucleophile-sequestered metal complexes and radicals, limiting the nucleophile scope to sterically uncongested ones. The coupling of sterically congested nucleophiles poses a significant challenge due to difficulties in transmetalation, restricting the reaction generality. Here, we describe a probable outer-sphere nucleophilic attack mechanism that circumvents the challenging transmetalation associated with sterically congested nucleophiles. This strategy enables a general copper-catalyzed enantioconvergent radical N-alkylation of aromatic amines with secondary/tertiary alkyl halides and exhibits catalyst-controlled stereoselectivity. It accommodates diverse aromatic amines, especially bulky secondary and primary ones to deliver value-added chiral amines (>110 examples). It is expected to inspire the coupling of more nucleophiles, particularly challenging sterically congested ones, and accelerate reaction generality.

Enantioselective propargylic amination and related tandem sequences to α-tertiary ethynylamines and azacycles

Chiral α-tertiary amines and related azacycles are sought-after compounds for drug development. Despite progress in the catalytic asymmetric construction of aza-quaternary stereocentres, enantioselective synthesis of multifunctional α-tertiary amines remains underdeveloped. Enantioenriched α-disubstituted α-ethynylamines are attractive synthons for constructing chiral α-tertiary amines and azacycles, but methods for their catalytic enantioselective synthesis need to be expanded. Here we describe an enantioselective asymmetric Cu(I)-catalysed propargylic amination (ACPA) of simple ketone-derived propargylic carbonates to give both α-dialkylated and α-alkyl-α-aryl α-tertiary ethynylamines. Sterically confined pyridinebisoxazoline (PYBOX) ligands, with a C4 shielding group and relaying groups, play a key role in achieving excellent enantioselectivity. The syntheses of quaternary 2,5-dihydropyrroles, dihydroquinines, dihydrobenzoquinolines and dihydroquinolino[1,2-α]quinolines are reported, and the synthetic value is further demonstrated by the enantioselective catalytic total synthesis of a selective multi-target β-secretase inhibitor. Enantioselective Cu-catalysed propargylic substitutions with O- and C-centred nucleophiles are also realized, further demonstrating the potential of the PYBOX ligand.

Metal-free synthesis of propargylamines via light-mediated persulfate activation and phase-transfer catalysis

We present a metal-free method to synthesize secondary and tertiary propargylamines from primary and secondary amines and alkynes using light-mediated persulfate activation and phase-transfer catalysis. Our method explores a tandem oxidative coupling/alkynylation reaction for the generation of diverse compounds, highlighting the sustainability of the process and its wide scope.

Catalytic Enantioselective Alkyne Addition to Nitrones Enabled by Tunable Axially Chiral Imidazole-Based P,N-Ligands

Although catalytic enantioselective alkyne addition is an established method for the synthesis of chiral propargylic alcohols and amines, addition to nitrones presents unique challenges, and no general chiral catalyst system has been developed. In this manuscript, we report the first Cu-catalyzed enantioselective alkyne addition to nitrones utilizing tunable axially chiral imidazole-based P,N-ligands. Our approach effectively overcomes difficulties in both reactivity and selectivity, resulting in a simple Cu-catalyzed protocol. The reaction accommodates a wide range of nitrones and alkynes, enabling the streamlined synthesis of chiral propargyl N-hydroxylamines via the enantioselective C-C bond formation. A diverse array of optically active nitrogen-containing compounds, including chiral hydroxylamines, can be accessed directly through facile transformations of the reaction products.

Silver and Gold Complexes with NHC-Ligands Derived from Caffeine: Catalytic and Pharmacological Activity

N-heterocyclic carbene (NHC) silver(I) and gold(I) complexes have found different applications in various research fields, as in medicinal chemistry for their antiproliferative, anticancer, and antibacterial activity, and in chemistry as innovative and effective catalysts. The possibility of modulating the physicochemical properties, by acting on their ligands and substituents, makes them versatile tools for the development of novel metal-based compounds, mostly as anticancer compounds. As it is known, chemotherapy is commonly adopted for the clinical treatment of different cancers, even though its efficacy is hampered by several factors. Thus, the development of more effective and less toxic drugs is still an urgent need. Herein, we reported the synthesis and characterization of new silver(I) and gold(I) complexes stabilized by caffeine-derived NHC ligands, together with their biological and catalytic activities. Our data highlight the interesting properties of this series as effective catalysts in A3-coupling and hydroamination reactions and as promising anticancer, anti-inflammatory, and antioxidant agents. The ability of these complexes in regulating different pathological aspects, and often co-promoting causes, of cancer makes them ideal leads to be further structurally functionalized and investigated.

Reactive Vapor-Phase Inhibitors for Area-Selective Depositions at Tunable Critical Dimensions

Area-selective depositions (ASD) take advantage of the chemical contrast between material surfaces in device fabrication, where a film can be selectively grown by chemical vapor deposition on metal versus a dielectric, for instance, and can provide a path to nontraditional device architectures as well as the potential to improve existing device fabrication schemes. While ASD can be accessed through a variety of methods, the incorporation of reactive moieties in inhibitors presents several advantages, such as increasing thermal stability and limiting precursor diffusion into the blocking layer. Alkyne-terminated small molecule inhibitors (SMIs)─propargyl, dipropargyl, and tripropargylamine─were evaluated as metal-selective inhibitors. Modeling these SMIs provided insight into the binding mechanism, influence of sterics, and complex polymer network formed from the reaction between inhibitors consisting of alkene, aromatic, and network branchpoints. While a significant contrast in the binding of the SMIs on copper versus a dielectric was observed, residual amounts were detected on the dielectric surfaces, leading to variable ALD growth rates dependent on pattern-critical dimensions. This behavior can be controlled and utilized to direct film growth on patterns only above a critical threshold dimension; below this threshold, both the dielectric and metal features are protected. This method provides another design parameter for ASD processes and may extend its application to broader-ranging device fabrication schemes.

Eco-friendly and sustainable basil seed hydrogel-loaded copper hydroxide-based catalyst for the synthesis of propargylamines and tetrazoles

The broad use of propargyl amines and tetrazoles in pharmaceutical applications presents a well-established challenge. Their synthesis relies heavily on catalysis, which, in turn, has been hindered by the scarcity of stable and practical catalysts. In response to this issue, we have developed an environmentally friendly and sustainable catalyst by infusing copper hydroxide into basil seed hydrogel (Cu(OH)2-BSH), creating a 3D nanoreactor support structure. To verify the structural, physical, chemical, and morphological properties of the prepared samples, a comprehensive analysis using various techniques, including FT-IR, EDX, FE-SEM, TEM, XRD, BET, TGA, and XPS, were conducted. The results not only confirmed the presence of Cu(OH)2 but also revealed a porous structure, facilitating faster diffusion and providing a substantial number of active sites. This catalyst boasts a high surface area and can be easily recovered, making it a cost-effective, safe, and readily available option. This catalyst was applied to the synthesis of propargyl amines and tetrazoles through multi-component reactions (MCRs), achieving excellent results under mild conditions and in a remarkably short timeframe. Consequently, this work offers a straightforward and practical approach for designing and synthesizing metal hydroxides and 3D hydrogels for use in heterogeneous catalysis during organic syntheses. This can be achieved using basic and affordable starting materials at the molecular level.

A Regioselective [3 + 2] Cycloaddition of Alkynols and Ketones To Access Diverse 1,3-Dioxolane Scaffolds

This study presents a stepwise exoselective [3 + 2] cycloaddition reaction of alkynols with ketones, leading to the synthesis of 4-methylene-1,3-dioxolane derivatives. Remarkably, without any Thorpe-Ingold induced effect, the cyclization reaction was demonstrated with complete regio- and chemoselectivity, which was solely promoted by cesium carbonate. A wide range of unactivated ketones are viable under these mild reaction conditions, and both primary and tertiary alkynols are compatible with these cyclization reactions. We have prepared a diverse array of highly dense exomethylene 1,3-dioxolane rings demonstrating a remarkable tolerance for various functional groups.

Amidative Cyclization of Alkynyl Esters to Access Pyrazin-1(2H)-ones: Application to the Synthesis of Peramine and Dibromophakellin

Herein, we report an efficient 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed tandem intermolecular amidation and regioselective intramolecular 6-exo-dig cyclization of alkynyl esters to efficiently access pyrazine-1(2H)-one scaffolds. This organo-catalyzed [5 + 1] annulation features a broad substrate scope concerning both annulating partners. Total syntheses of peramine and formal syntheses of dibromophakellin natural products were achieved to show the application potential of the method.

Synthesis of a new fluorophore: wavelength-tunable bisbenzo[f]isoindolylidenes

The creation of new functional molecules is a central task in chemical synthesis. Herein, we report the synthesis of a new type of fluorophore, bisbenzo[f]isoindolylidenes, from easily accessible dipropargyl benzenesulfonamides. Wavelength-tunable fluorophores emitting strong fluorescence of green to red light were obtained in this reaction. Late-stage modifications and incorporation of bioactive molecules into these fluorophores give rise to potential applications in biological studies. Detailed computational and experimental studies were conducted to elucidate the mechanism, and suggest a reaction sequence involving Garratt-Braverman type cyclization, isomerization, fragmentation, dimerization and oxidation.

The Development of Aldehyde Catalytic System

Aldehyde catalysts have proven to be highly effective in facilitating and accelerating a wide range of challenging transformations in organic chemistry. This article is structured into three main sections, focusing on the utilization of aldehydes as organocatalysts, the aldehydes/transition metals catalytic systems, and photochemical initiators. Finally, we provide a concise summary of the advancements in this fascinating research field, offering our perspectives and insights.

Base-Promoted [4 + 2] Annulation Reaction of In Situ-Generated Azadienes from N-Propargylamines with Active Methylene Compounds: Access to Highly Functionalized 2-Pyridones

A facile and efficient synthesis of structurally diversified 2-pyridones is demonstrated using the [4 + 2] annulation of in situ generated azadienes from N-propargylamines and active methylene compounds. The reaction is promoted by an inorganic base giving moderate to good yields. The developed methodology is applicable for the direct and formal synthesis of various bioactive molecules. The synthetic utility of the protocol was also illustrated by late-stage functionalization of the products.

A Highly Stereoselective Redox Isomerization-Reductive Deuteration Sequence of Propargyl Amines to α-Deuterated Amino Acids

Herein, we report a Cu-catalyzed redox isomerization-reductive deuteration sequence, providing facile access to a range of α-deuterated amino acid esters featuring an Z-configured alkene moiety with high yields. The advantages of this sequence include mild conditions, broad substrate scope, and excellent stereoselectivity. This research also represents a rare example of the Z-selective redox isomerization of propargyl amines.

Atomically precise ultrasmall copper cluster for room-temperature highly regioselective dehydrogenative coupling

Three-component dehydrogenative coupling reactions represent important and practical methodologies for forging new C-N bonds and C-C bonds. Achieving highly all-in-one dehydrogenative coupling functionalization by a single catalytic system remains a great challenge. Herein, we develop a rigid-flexible-coupled copper cluster [Cu3(NHC)3(PF6)3] (Cu3NC(NHC)) using a tridentate N-heterocyclic carbene ligand. The shell ligand endows Cu3NC(NHC) with dual attributes, including rigidity and flexibility, to improve activity and stability. The Cu3NC(NHC) is applied to catalyze both highly all-in-one dehydrogenative coupling transformations. Mechanistic studies and density functional theory illustrate that the improved regioselectivity is derived from the low energy of ion pair with copper acetylide and endo-iminium ions and the low transition state, which originates from the unique physicochemical properties of the Cu3NC(NHC) catalyst. This work highlights the importance of N-heterocyclic carbene in the modification of copper clusters, providing a new design rule to protect cluster catalytic centers and enhance catalysis.

Catalytic enantioselective reductive alkynylation of amides enables one-pot syntheses of pyrrolidine, piperidine and indolizidine alkaloids

The primary objective in synthetic organic chemistry is to develop highly efficient, selective, and versatile synthetic methodologies, which are essential for discovering new drug candidates and agrochemicals. In this study, we present a unified strategy for a one-pot, catalytic enantioselective synthesis of α-alkyl and α,α'-dialkyl pyrrolidine, piperidine, and indolizidine alkaloids using readily available amides and alkynes. This synthesis is enabled by the identification and development of an Ir/Cu/N-PINAP catalyzed highly enantioselective and chemoselective reductive alkynylation of α-unbranched aliphatic amides, which serves as the key reaction. This reaction is combined with Pd-catalyzed tandem reactions in a one-pot approach, enabling the collective, catalytic enantioselective total syntheses of eight alkaloids and an anticancer antipode with 90-98% ee. The methodology's enantio-divergence is exemplified by the one-step access to either enantiomer of alkaloid bgugaine.

Magnetic nanoparticles modified with a copper(i) complex as a novel and efficient reusable catalyst for A3 coupling leading to C-N bond formation

Propargylamines are an important and valuable family of nitrogen-containing compounds with many applications in the fields of medical, industrial, and chemical processes. One-pot multicomponent A3 coupling reactions of aldehydes, amines, and alkynes in the presence of transition metals as catalysts is an efficient strategy for preparing propargylamines. In this study, we fabricated a novel magnetically reusable copper nanocatalyst [Fe3O4-BIm-Pyrim-CuI] through the immobilization of the copper(i) complex on the surface of the magnetic nanoparticles modified with benzimidazole-pyrimidine ligand and evaluated its catalytic activity in the preparation of propargylamines through one-pot multicomponent A3 coupling reactions of aldehydes, amines, and alkynes. Under this catalytic system, aryl substrates with both electron-donating and electron-withdrawing substituents also gave the desired products in excellent yields under standardized conditions. The Fe3O4-BIm-Pyrim-CuI catalyst was easily separated using an external magnet, and the recovered catalyst was reused in 8 cycles without significant loss of activity.

Enantioselective Alkynylation of 2-Aryl-3H-indol-3-ones via Cooperative Catalysis of Copper/Chiral Phosphoric Acid

A facile enantioselective alkynylation of cyclic ketimines attached to a neutral functional group utilizing the dual Cu(I)-CPA catalysis is described. The strategy of the alkynylation of 2-aryl-3H-indol-3-one directly to chiral propargylic amines containing indolin-3-one moiety in good yields and enantioselectivities. Moreover, gram-scale synthesis of chiral propargylamines based C2-quaternary indolin-3-ones was performed. The synthetic applications were confirmed by transformations of the products with no decrease in the yield and enantioselectivity.

Highly Selective Cyclization and Isomerization of Propargylamines to Access Functionalized Quinolines and 1-Azadienes

Developing new organic reactions with excellent atom economy and high selectivity is significant and urgent. Herein, by ingeniously regulating the reaction conditions, highly selective transformations of propargylamines have been successfully implemented. The palladium-catalyzed cyclization of propargylamines generates a series of functionalized quinoline heterocycles, while the base-promoted isomerization of propargylamines affords diverse 1-azadienes. Both reactions have good functional group tolerance, mild conditions, excellent atom economy and high yields of up to 93%. More importantly, these quinoline heterocycles and 1-azadienes could be flexibly transformed into valuable compounds, illustrating the validity and practicability of the propargylamine-based highly selective reactions.

Domino Approach for the Synthesis of Pyridinium Salts and 1,2,3,8a-Tetrahydroimidazo[1,2-a]pyridines from 2-Imidazolines and Propiolic Acid Esters

Adducts of 1-alkyl-2-imidazolines and two molecules of alkyl propiolate, possessing an N-propargyl-β-enaminoester fragment, easily undergo a domino reaction to form pyridinium salts with β-(alkylammonio)ethyl group at the nitrogen atom in the presence of 2 equiv of a protic acid. Treatment of the above reaction mixture with a base gives 1,2,3,8a-tetrahydroimidazo[1,2-a]pyridines. Reaction of the latter compounds with acid chlorides affords pyridinium salts with β-(alkylamido)ethyl moiety at the nitrogen atom.

Bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction for construction of 5-oxazoylmethyl α-silyl alcohol

A bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction was developed. The reaction proceeded well with a broad range of N-propargylamides and acylsilanes, affording the target chiral 5-oxazoylmethyl α-silyl alcohols in up to 95% yield and 99% ee under mild conditions. Importantly, this facile protocol was available for the late-stage modification of several bioactive molecules. Based on the mechanistic study and control experiments, a possible catalytic cycle and transition state are proposed to elucidate the reaction process and enantioinduction.

Regio- and Enantioselective Catalytic δ-C-H Amidation of Dioxazolones Enabled by Open-Shell Copper-Nitrenoid Transfer

Controlling regio- and enantioselectivity in C-H functionalization reactions is of paramount importance due to their versatile synthetic utilities. Herein, we describe a new approach for the asymmetric δ-C(sp³)-H amidation catalysis of dioxazolones using a Cu(I) precursor with a chiral bisoxazoline ligand to access six-membered lactams with high to excellent regio- and enantioselectivity (up to >19:1 rr and >99:1 er). Combined experimental and computational mechanistic studies unveiled that the open-shell character of the postulated Cu-nitrenoids enables the regioselective hydrogen atom abstraction and subsequent enantio-determining radical rebound of the resulting carbon radical intermediates. The synthetic utility of this asymmetric cyclization was demonstrated in the diastereoselective introduction of additional functional groups into the chiral δ-lactam skeleton as well as in the rapid access to biorelevant azacyclic compounds.

Copper-Catalyzed Enantioconvergent Radical C(sp3)-N Cross-Coupling of Activated Racemic Alkyl Halides with (Hetero)aromatic Amines under Ambient Conditions

The enantioconvergent C(sp³)-N cross-coupling of racemic alkyl halides with (hetero)aromatic amines represents an ideal means to afford enantioenriched N-alkyl (hetero)aromatic amines yet has remained unexplored due to the catalyst poisoning specifically for strong-coordinating heteroaromatic amines. Here, we demonstrate a copper-catalyzed enantioconvergent radical C(sp³)-N cross-coupling of activated racemic alkyl halides with (hetero)aromatic amines under ambient conditions. The key to success is the judicious selection of appropriate multidentate anionic ligands through readily fine-tuning both electronic and steric properties for the formation of a stable and rigid chelating Cu complex. Thus, this kind of ligand could not only enhance the reducing capability of a copper catalyst to provide an enantioconvergent radical pathway but also avoid the coordination with other coordinating heteroatoms, thereby overcoming catalyst poisoning and/or chiral ligand displacement. This protocol covers a wide range of coupling partners (89 examples for activated racemic secondary/tertiary alkyl bromides/chlorides and (hetero)aromatic amines) with high functional group compatibility. When allied with follow-up transformations, it provides a highly flexible platform to access synthetically useful enantioenriched amine building blocks.

Copper-catalysed enantioconvergent alkylation of oxygen nucleophiles

Carbon-oxygen bonds are commonplace in organic molecules, including chiral bioactive compounds; therefore, the development of methods for their construction with simultaneous control of stereoselectivity is an important objective in synthesis. The Williamson ether synthesis, first reported in 18501, is the most widely used approach to the alkylation of an oxygen nucleophile, but it has significant limitations (scope and stereochemistry) owing to its reaction mechanism (SN2 pathway). Transition-metal catalysis of the coupling of an oxygen nucleophile with an alkyl electrophile has the potential to address these limitations, but progress so far has been limited2-7, especially with regard to controlling enantioselectivity. Here we establish that a readily available copper catalyst can achieve an array of enantioconvergent substitution reactions of α-haloamides, a useful family of electrophiles, by oxygen nucleophiles; the reaction proceeds under mild conditions in the presence of a wide variety of functional groups. The catalyst is uniquely effective in being able to achieve enantioconvergent alkylations of not only oxygen nucleophiles but also nitrogen nucleophiles, giving support for the potential of transition-metal catalysts to provide a solution to the pivotal challenge of achieving enantioselective alkylations of heteroatom nucleophiles.

Photocatalytic Benzylic C-H Oxidation/Cyclization of Enaminones to the Synthesis of Polysubstituted Oxazoles

Photocatalytic benzylic C-H oxidation/cyclization of enaminones was efficiently achieved to afford oxazole derivatives under mild conditions. The oxygen in the oxazole ring originated from green oxidant molecular oxygen. The synthetic protocol features broad substrate scopes and good functional group tolerance. The combined experimental and theoretical studies reveal that in suit benzylic C-H oxidation/cyclization is involved in the reaction transformations.

Synthesis of Ag-Cu-Ni Nanoparticles Stabilized on Functionalized g-C3N4 and Investigation of Its Catalytic Activity in the A3-Coupling Reaction

In the present research, using ethylenediamine and hydrazine hydrate as the capping and reducing agents in this investigation, respectively, Ag-Cu-Ni NPs were immobilized on the functionalized g-C₃N₄ surface. This nanocatalyst was studied in terms of its catalytic activities for the A³-coupling reaction to synthesize propargylamine derivatives. According to the results, in the presence of 1 mL of toluene as the solvent and 20 mg of the g-C₃N₄-TCT-2AEDSEA-Ag-Cu-Ni nanocatalyst, the maximum efficiency of the nanocatalyst occurred at a temperature of 80 °C. Products were purified using thin-layer chromatography plates (silica gel) by employing n-hexane/ethyl acetate with a 90:10 ratio. In addition, the prominent benefits of the synthesized nanocatalyst include its high yields of the product, cost-effectiveness, recyclability, and easy separation. The novelty of the catalyst is due to the presence of Ag-Cu-Ni nanoparticles at the same time in the structure of the functionalized g-C₃N₄ substrate. So, Ag-Cu-Ni can be strongly connected to the substrate. The structure of the synthesized nanocatalyst was characterized using Fourier transformed infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating-sample magnetometry, and transmission electron microscopy.

Rapid Construction of Tricyclic Furanobenzodihydropyrans by Asymmetric Tandem Reaction

A process based on the organocatalyzed Mannich/cycloketalization/transesterification tandem reaction of 1-(2-hydroxyaryl)-1,3-diketones and β,γ-alkynyl α-imino esters has been developed, delivering a variety of tricyclic furanobenzodihydropyrans with excellent results (up to 99% yield, 99% ee, and >19:1 dr).

Catalytic Methylene Insertion between Amines and Terminal Alkynes via C-N Bond Cleavage of N,N-Dimethylacetamide: A Unique Route to Propargylic Amines

A copper-based system allows for the methylene insertion between an amine and a milder nucleophile, including a terminal alkyne counterpart, via C-N bond cleavage of N,N-dimethylacetamide. The method gives an expedient access to propargylic amines in good to excellent yields. A wide-ranging substrate scope and late-stage functionalization of complex molecules make the protocol practically valuable.

Cadmium-Doped and Pincer Ligand-Modified Gold Nanocluster for Catalytic KA2 Reaction

A gold nanocluster Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ (PNP=2,6-bis(diphenylphosphinomethyl)pyridine, SR=4-MeOPhS) consisting of an icosahedral Au₁₃ kernel, two Au₂ CdS₆ staple motifs, and two PNP pincer ligands has been designed, synthesized and well characterized. This cadmium and PNP pincer ligand co-modified gold nanocluster showed high catalytic efficiency in the KA² reaction, featuring high TON, mild reaction conditions, broad substrate scope as well as catalyst recyclability. Comparison of the catalytic performance between Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ and the structurally similar single cadmium (or PNP) modified gold nanoclusters demonstrates that the co-existence of the cadmium and PNP on the surface is crucial for the high catalytic activity of the gold nanocluster. This work would be enlightening for developing efficient catalysts for cascade reactions and discovering the catalytic potential of metal nanoclusters in organic transformations.

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.

Synthesis of dithioacetals via gold-catalysed hydrothiolation of vinyl sulfides

The synthesis of unsymmetrical dithioacetals based on gold catalysis is described. Although many approaches to the preparation of symmetrical dithioacetals have been developed, the methods to access unsymmetrical ones remain limited. In this regard, we report a mild synthetic method with a broad substrate scope. Screening of various gold catalysts identified a catalyst, which allows the hydrothiolation of both activated and unactivated vinyl sulfides with high efficiency. Moreover, the reaction displays broad compatibility for both aryl and aliphatic thiols.

Propargylamine Amino Acids as Constrained Nε-Substituted Lysine Mimetics

Herein, alkylated propargylamines are reported as constrained lysine mimetics and constructed in a single step using a copper(I)-catalyzed A³-coupling reaction. Using multiple secondary amines, the reaction allowed the generation of a structurally diverse set of N-Fmoc protected amino acid derivatives. In addition, the A³-reaction was applied on solid phase via the assembly of short model tripeptides. Moreover, the internal alkyne moiety allowed further functionalization toward novel 1,4,5-trisubstituted 1,2,3-triazole-based amino acids.

Propargylamine: an important moiety in drug discovery

Propargylamine is a chemical moiety whose properties have made it a widely distributed group within the fields of medicinal chemistry and chemical biology. Its particular reactivity has traditionally popularized the preparation of propargylamine derivatives using a large variety of synthetic strategies, which have facilitated the access to these compounds for the study of their biomedical potential. This review comprehensively covers and analyzes the applications that propargylamine-based derivatives have achieved in the drug discovery field, both from a medicinal chemistry perspective and from a chemical biology-oriented approach. The principal therapeutic fields where propargylamine-based compounds have made an impact are identified, and a discussion of their influence and growing potential is included.

Tetra(phenylethynyl)tin Is a New Reagent for Solvent-Free Alkynylation of Imines

The first ZnCl2-catalyzed alkynylation of aldimines with tetra(phenylethynyl)tin was achieved under solvent-free conditions. The present methodology provides propargylamines in 38–62% yields.

Design, Synthesis and Assay of Novel Methylxanthine-Alkynylmethylamine Derivatives as Acetylcholinesterase Inhibitors

Xanthine derivatives have been a great area of interest for the development of potent bioactive agents. Thirty-eight methylxanthine derivatives as acetylcholinesterase inhibitors (AChE) were designed and synthesized. Suzuki-Miyaura cross-coupling reactions of 8-chlorocaffeine with aryl(hetaryl)boronic acids, the CuAAC reaction of 8-ethynylcaffeine with several azides, and the copper(I) catalyzed one-pot three-component reaction (A³-coupling) of 8-ethynylcaffeine, 1-(prop-2-ynyl)-, or 7-(prop-2-ynyl)-dimethylxanthines with formaldehyde and secondary amines were the main approaches for the synthesis of substituted methylxanthine derivatives (yield 53-96%). The bioactivity of all new compounds was evaluated by Ellman's method, and the results showed that most of the synthesized compounds displayed good and moderate acetylcholinesterase (AChE) inhibitory activities in vitro. The structure-activity relationships were also discussed. The data revealed that compounds 53, 59, 65, 66, and 69 exhibited the most potent inhibitory activity against AChE with IC₅₀ of 0.25, 0.552, 0.089, 0.746, and 0.121 μM, respectively. The binding conformation and simultaneous interaction modes were further clarified by molecular docking studies.

Multicatalysis protocol enables direct and versatile enantioselective reductive transformations of secondary amides

The catalytic asymmetric geminal bis-nucleophilic addition to nonreactive functional groups is a type of highly desirable yet challenging transformation in organic chemistry. Here, we report the first catalytic asymmetric reductive/deoxygenative alkynylation of secondary amides. The method is based on a multicatalysis strategy that merges iridium/copper relay catalysis with organocatalysis. A further combination with the palladium-catalyzed alkyne hydrogenation allows the one-pot enantioselective reductive alkylation of secondary amides. This versatile protocol allows the efficient synthesis of four types of α-branched chiral amines, which are prevalent structural motifs of active pharmaceutical ingredients. The protocol also features excellent enantioselectivity, chemoselectivity, and functional group tolerance to be compatible with more reactive functional groups such as ketone and aldehyde. The synthetic utility of the method was further demonstrated by the late-stage functionalization of two drug derivatives and the concise, first catalytic asymmetric approach to the κ-opioid antagonist aticaprant.

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.