Domino Coupling Relay Approach to Polycyclic Pyrrole-2-carboxylates

Rapid Access to Divergent Fused Polycycles Via One-Pot A3 Coupling and Intramolecular Diels-Alder Reaction

Divergent nitrogen-containing fused polycyclic ring systems are constructed from simple starting materials via a one-pot aldehyde-alkyne-amine (A3) coupling and intramolecular Diels-Alder reaction. This domino reaction directly furnishes linear 5/5/5 and 5/5/6, or nonlinear 5/5/6/5, polycyclic rings containing an oxa-bridged fused 5/5 bicycle and a 1,6-enyne substructure. One-step derivation of the oxa-bridged 5/5 bicycle leads to a polyfunctionalized 5/5 bicycle with tetrahydrofuran fused back-to-back to pyrroline or a 6/5 bicycle with the hexahydro-1H-isoindole structure, while cycloisomerizing the enyne substructure adds an extra fused 5-membered ring to afford functionalized linear 5/5/5/5 or 5/5/5/5/5 fused ring systems from selected substrates. In addition, the one-pot product can be designed so that the alkyne moiety is hydroalkoxylated to form an additional heterocyle in a linear 5/5/5/6 or nonlinear 5/5/6/5/5 ring system. This diversity-oriented synthetic approach thus allows rapid access to an under-explored structural space for discovery of new biological or non-biological activities or functions.

Rhodium(II)-Catalyzed Alkynyl Carbene Insertion into N-H Bonds

The first insertion of an alkynyl carbene into N-H bonds under Rh-catalysis is developed. Alkynyl hydrazone carboxylates are used as donor-acceptor carbene precursors and are exquisitely inserted into the N-H bonds of various amines, amides, and 1,2-diamines. A wide variety of 3-alkynyl 3,4-dihydroquinoxalin-2(1H)-ones and densely functionalized α-alkynyl α-amino esters are obtained in good to excellent yields. Further, chemoselective N-H insertion reactions, mechanistic studies, and various synthetic transformations for obtaining valuable heterocycles are demonstrated.

A Density Functional Theory Study on the Cobalt-Mediated Intramolecular Pauson–Khand Reaction of Enynes Containing a Vinyl Fluoride Moiety

The Co2(CO)8-mediated intramolecular Pauson–Khand reaction (PKR) is an effective method for constructing polycyclic structures. Recently, our group reported a series of this type of reaction involving fluorinated enynes that proceed with reasonable reaction rates and yields. However, mechanistic studies involving these fluorinated derivatives in intramolecular PKR are scarce. In this study, density functional theory calculations are used to clarify the mechanism and reactivity of enynes containing a vinyl fluoride moiety for this reaction. In agreement with previous studies, alkene insertion is considered to be the rate-determining step for the overall Pauson–Khand reaction of enynes containing a vinyl fluoride moiety. The effect of the substituent on the Co2(CO)8-mediated intramolecular Pauson–Khand reaction has also been investigated. When introducing heteroatoms as tethering units, the fluorinated enynes exhibited lower reactivity than the malonate homologues, whereas the use of a sulfur-based tether was unsuccessful. This computational study provides detailed information about the PKR mechanism and transition-state structures, and the results are validated with previous experimental results.

Formal nucleophilic pyrrolylmethylation via palladium-based auto-tandem catalysis: switchable regiodivergent synthesis and remote chirality transfer

Although nucleophilic benzylation-type reaction to introduce various aromatic systems into molecules has been widely explored, the related pyrrolylmethylation version remains to be disclosed. Reported herein is a palladium-catalysed multiple auto-tandem reaction between N-Ts propargylamines, allyl carbonates and aldimines in the presence of an acid, proceeding through sequential allylic amination, cycloisomerisation, vinylogous addition and aromatisation steps. A diversity of formal pyrrolylmethylated amine products were finally furnished efficiently. In addition, switchable regiodivergent 3-pyrrolylmethylation and 4-pyrrolylmethylation were realised by tuning catalytic conditions. Moreover, remote chirality transfer with readily available enantioenriched starting materials was well achieved with an achiral ligand, relying on diastereoselective generation of η2-Pd(0) complexes between Pd(0) and chiral 1,3-diene intermediates in the key vinylogous addition step. A few control experiments were conducted to elucidate the palladium-involved tandem reaction and regiodivergent synthesis.

Visible Light-Promoted Green and Sustainable Approach for One-Pot Synthesis of 4,4'-(Arylmethylene)bis(1H-pyrazol-5-ols), In Vitro Anticancer Activity, and Molecular Docking with Covid-19 Mpro

A visible light-promoted, efficient, green, and sustainable strategy has been adopted to unlatch a new pathway toward the synthesis of a library of medicinally important 4,4'-(arylmethylene)bis(1H-pyrazol-5-ols) moieties using substituted aromatic aldehydes and sterically hindered 3-methyl-1-phenyl-2-pyrazoline-5-one in excellent yield. This reaction shows high functional group tolerance and provides a cost-effective and catalyst-free protocol for the quick synthesis of biologically active compounds from readily available substrates. Synthesized compounds were characterized by spectroscopic techniques such as IR, 1HNMR, 13CNMR, and single-crystal XRD analysis. All the synthesized compounds were evaluated for their antiproliferative activities against a panel of five different human cancer cell lines and compared with Tamoxifen using MTT assay. Compound 3m exhibited maximum antiproliferative activity and was found to be more active as compared to Tamoxifen against both the MCF-7 and MDA-MB-231 cell lines with an IC50 of 5.45 and 9.47 μM, respectively. A molecular docking study with respect to COVID-19 main protease (Mpro) (PDB ID: 6LU7) has also been carried out which shows comparatively high binding affinity of compounds 3f and 3g (-8.3 and -8.8 Kcal/mole, respectively) than few reported drugs such as ritonavir, remdesivir, ribacvirin, favipiravir, hydroxychloroquine, chloroquine, and olsaltamivir. Hence, it reveals the possibility of these compounds to be used as effective COVID-19 inhibitors.

One-Pot Synthesis of Symmetrical and Asymmetrical 3-Amino Diynes via Cu(I)-Catalyzed Reaction of Enaminones with Terminal Alkynes

An economical and efficient protocol for the direct construction of amino skipped diynes through the Cu(I)-catalyzed reaction of enaminones and terminal alkynes has been described. Different kinds of symmetrical and asymmetrical 3-amino diynes could be obtained in up to 83% yield through a one-pot reaction under mild conditions.

Microwave-Assisted Cu(I)-Catalyzed Synthesis of Unsymmetrical 1,4-Diamino-2-butynes via Cross-A3-Coupling/Decarboxylative A3-Coupling

1,4-Diamino-2-butynes display both chemical and physiological properties. Here a highly efficient synthesis avenue to generate unsymmetric 1,4-diamino-2-butynes has been developed by microwave-assisted Cu(I)-catalyzed cross-A³-coupling/decarboxylative coupling of two different amines, formaldehyde, and propiolic acid through a domino process. This multicomponent reaction provides a series of target products in moderate to good yields with high chemoselectivity.

Ribose conversion with amino acids into pyrraline platform chemicals - expeditious synthesis of diverse pyrrole-fused alkaloid compounds

One-pot conversion of sustainable d-ribose with l-amino acid, methyl esters produced pyrrole-2-carbaldehydes 5 in reasonable yields (32-63%) under pressurized conditions of 2.5 atm at 80 °C. The value-added pyrraline compounds 5 as platform chemicals were utilized for quick installation of poly-heterocyclic cores for the development of pyrrole-motif natural and artificial therapeutic agents. A pyrrole-fused piperazin-2-one scaffold 6 was prepared by reductive amination of pyrralines 5 with benzylamine. While further cyclization of pyrralines 5 with ethane-1,2-diamine produced pyrrolo-piperazin-2-ones 7 with an extra imidazolidine ring, the reaction with 2-amino alcohols derived from natural l-amino acids, alanine, valine, and phenylalanine, respectively provided pyrrolo-piperazin-2-ones 8, 9, and 10 with oxazolidine as the third structural core. Cell viability and an anti-inflammatory effect of the synthesized compounds were briefly tested by the MTT method and the Griess assay, among which 8h and 10g exhibited significant anti-inflammatory effects with negligible cell toxicity.

Copper-catalyzed tandem annulation of 2-alkynoyl-2′-iodo-1,1′-biphenyls with isocyanoacetates: a rapid access to pyrrole-fused tetracyclic skeletons

A copper-catalyzed [3 + 2] cycloaddition/C–C coupling tandem process was developed based on the concept of trapping organocuprate intermediates.

Nanofibrils of a CuII-Thiophenyltriazine-Based Porous Polymer: A Diverse Heterogeneous Nanocatalyst

Herein, we report knitting of a thiophenyltriazine-based porous organic polymer (TTPOP) with high surface area and high abundance of nitrogen and sulfur sites, synthesized through a simple one-step Friedel-Crafts reaction of 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine and formaldehyde dimethyl acetal in the presence of anhydrous FeCl₃, and thereafter grafting of Cu(OAc)₂·H₂O in the porous polymer framework to achieve the potential catalyst (Cu^II-TTPOP). TTPOP and Cu^II-TTPOP were characterized thoroughly utilizing solid-state ¹³C-CP MAS NMR, Fourier transform infrared, wide-angle powder X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy and surface imaging by transmission electron microscopy and field emission scanning electron microscopy. The porosity of the nanomaterials was observed in the surface imaging and verified through conducting N₂ gas adsorption techniques. Keeping in mind the tremendous importance of C-C and C-N coupling and cyclization processes, the newly synthesized Cu^II-TTPOP was employed successfully for a wide range of organic catalytic transformations under mild conditions to afford directly valuable diindolylmethanes and spiro-analogues, phthalimidines, propargyl amines, and their sugar-based chiral compounds with high yields using readily available substrates. The highly stable new heterogeneous catalyst showed outstanding sustainability, robustness, simple separation, and recyclability.

Highly enantioselective copper-catalyzed propargylic amination to access N-tethered 1,6-enynes

A highly enantioselective copper-catalyzed propargylic amination has been developed with a new chiral N,N,P ligand, providing a series of N-tethered 1,6-enynes in good to excellent yields with excellent enantioselectivities.

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.

Bio-crosslinking of chitosan with oxidized starch, its functionalization with amino acid and magnetization: As a green magnetic support for silver immobilization and its catalytic activity investigation

In this study, we have reported the synthesis and characterization of new magnetic bionanocatalyst based on chitosan and investigated their catalytic activity in the A³-coupling reaction. In order to increase the stability of chitosan, starch oxide biopolymer was used as a green covalent linking agent between chitosan chains. After the cross-linking of chitosan with starch oxide, aldehyde functional groups were reacted with amine groups of cysteine to form the corresponding Schiff bases in the hybrid biopolymer. Then, the imine bonds were reduced to prevent possible their hydrolysis. The magnetic support was resulted with addition of iron oxide nanoparticles. In the presence of thiol and carboxylate coordinated groups of amino acid, silver ions were immobilized on this biosupport.

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.

Diversified Cycloisomerization/Diels-Alder Reactions of 1,6-Enynes through Bimetallic Relay Asymmetric Catalysis

We report the combination of transition-metal-catalyzed diversified cycloisomerization of 1,6-enynes with chiral Lewis acid promoted asymmetric Diels-Alder reaction to realize asymmetric cycloisomerization/Diels-Alder relay reactions of 1,6-enynes with electron-deficient alkenes. A broad spectrum of chiral [5,6]-bicyclic products could be acquired in high yields (up to 99 %) with excellent diastereoselectivy (>19:1 dr) and enantioselectivity (up to 99 % ee).

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Post-synthetically modified MOF for the A3-coupling reaction of aldehyde, amine, and alkyne

A new heterogeneous NHC catalyst (Ag-NHC-MOF) was synthesized by the post-synthetic modification of an azolium-containing metal–organic framework.

Metal- and catalyst-free, one-pot, three-component synthesis of propargylamines in magnetized water: experimental aspects and molecular dynamics simulation

Multi-component reactions of aldehydes, amines, and alkynes in magnetized water as a green-promoting medium.

Iron-catalyzed alkynylation of tertiary aliphatic amines with 1-iodoalkynes to synthesize propargylamines

An alkynylation of tertiary aliphatic amines with 1-iodoalkynes has been developed in the presence of FeCl₂ as a catalyst and tert-butyl hydroperoxide as an oxidant.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.