Sonogashira Cross-coupling Research Articles

Hollow porous organic framework nanotube for efficient photocatalytic H2O2 generation by promoting H2O oxidation

The hydrogen peroxide (H2O2) generation by photocatalytic O2 reduction coupling H2O oxidation is a promising alternative to the traditional anthraquinone method. However, the low mass transfer and weak water oxidation are still the major responsible for the low efficiency of photocatalytic H2O2 production. Herein, we present a porous organic framework (BPTEE-POF) with hollow nanotube structure containing 2,2′-bipyridine active center of H2O oxidation, which was synthesized by template-free Sonogashira cross-coupling reaction of 5,5′-dibromo-2,2′-bipyridine (BP) and 1,1,2,2-tetrakis(4-ethynylphenyl)ethene (TEE). The 2,2′-bipyridine moieties can effectively weaken HO bond and facilitate H2O oxidation to generate O2 and H+, which can be subsequently employed as reactants for non-sacrificial H2O2 production. Meanwhile, the throughout hollow structure of BPTEE-POF is conducive to mass transfer/diffusion of substrate and product by siphoning, which promotes O2 and H2O molecules to contact with catalytic active sites and causes the quick dissociation of H2O2 from active sites, thereby boosting the overall reaction kinetic and efficiency.

Design of highly effective organic catalyst for hydrazine electrooxidation: Iodobenzo[b]furan derivatives

In this study, we investigate the electrochemical characteristics of 2-aryl/alkyl-3-iodobenzo[b]furans as anode catalysts for hydrazine (N2H4) fuel cells. Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques are employed to investigate the performance of these heteroaromatic compounds. The results demonstrate the promising potential of the 2-aryl/alkyl-3-iodobenzo[b]furans in fuel cell technology. Among the tested organic catalysts (2a, 2b, 2c, 2d, and 2e), 2a exhibited the highest electrocatalytic activity, giving a total current density of 26.62 mA/cm2 within the potential range of −0.4 to −0.8 V. 2-aryl/alkyl-3-iodobenzo[b]furans were synthesized by using palladium/copper-catalyzed Sonogashira cross-coupling reactions, followed by electrophilic cyclization with iodine (I2). All products were characterized using 1H and 13C NMR spectroscopy, confirming their structures and providing insights into their chemical properties.

Synthesis, structural characterization, and quantum chemical study of the 7-acetyl-5-nitrobenzofurans as anticancer agents with antioxidant properties

Synthesis of 7-acetyl-2-aryl-5-nitrobenzofurans 2a–j involved sequential Sonogashira cross-coupling of 2-hydroxy-3-iodo-5-nitroacetophenone with terminal acetylenes and in situ Cacchi-type cycloisomerization of 5-alkynylated intermediates. Hirshfeld's fingerprint diagrams and surface analysis showed varied intermolecular interactions. Additionally, intramolecular interactions were examined using DFT and QTAIM calculations. Benzofuran derivatives were tested for antiproliferative efficacy in vitro against MDA-MB-231 and Caski cell lines. The 1-(5-nitro-2-(p-tolyl)benzofuran-7-yl)ethan-1-one 2h showed promising antiproliferative activity against Caski and MDA-MB-231 cell lines, with IC50 values of 26.96 ± 4.97 µM and 5.13 ± 0.86 µM, respectively, compared to Camptothecin (IC50 = 8.96 ± 0.23 and 24.69 ± 0.26 µM). Derivatives with 2-(4-fluorophenyl)-2c, 2-(4-methoxyphenyl)- 2g, and 2-(3,5-bis(trifluoromethyl)phenyl)-2j groups showed significant antioxidant activity, with Fe-reducing power values of 520.14 ± 1.34 µM, 433.50 ± 1.30 µM, and 466.08 ± 1.91 µM, respectively, compared to ascorbic acid (IC50 = 538.05 µM). The most active molecules that docked with protease (2c, 2g, and 2j) and FKBP12-mTOR (2d, 2h and 2j) active site residues showed significant interactions which were confirmed by Molecular dynamic simulation. ADME investigation indicated drug-like characteristics, safe in silico toxicity, and no carcinogenic or mutagenicity.

Programmed Heterocycle Synthesis Using Halomucononitriles as Pyridinimine Precursors.

Herein we report a method to convert primary amines, ubiquitous motifs found in pharmaceutical libraries, to either imidazo[1,2-a]pyridines or 7-alkyl azaindoles in two steps from known compounds. Using halomucononitrile reagents, we can directly access 5-bromo-6-imino-1-alkyl-1,6-dihydropyridine-2-carbonitriles (pyridinimines) in a single step from primary amines (25-93% yield) through the cyclization of transient aminomucononitrile intermediates. We then demonstrate that these compounds can be readily converted to 7-alkylazaindoles using Sonogashira cross-coupling conditions (13 examples, up to 91% yield). Under oxidative conditions, the pyridinimines serve as directing groups for C-H functionalization reactions to afford imidazo[1,2-a]pyridines. We also studied the mechanism of the cyclization event using DFT calculations and propose that this takes place via sequential base-mediated E/Z isomerization and cyclization steps.

Difluoro Dipyridomethene Boron Complexes: Synthesis, Characterization, and Ab Initio Calculations.

Molecular engineering studies on the meso-cyano difluoro dipyridomethene boron complexes are presented and two series (a and b) of novel fluorophores are extensively studied. Halogenated derivatives were reacted under Suzuki-Miyaura or Sonogashira cross coupling reactions to introduce electron-donating or electron-withdrawing functional groups on positions 1 and 2 of the aromatic ligand. All derivatives were obtained in 14-90% yields and studied in detail by structural, photophysical, and computational analyses. Both series display excellent emissive properties in solution with blue to orange fluorescence emission upon blue light absorption and promising features as solid emitters. All the spectroscopic measurements are supported and confirmed by first-principles theoretical calculations combining TD-DFT and CC2. Series b, featuring an aryl substituent onto position 1 of the aromatic core, showed significantly large Stokes shifts values.

5‐Aryl Substituted 2‐(2‐Methoxyphenyl)benzoxazoles with Large Stokes Shifts: Synthesis, Crystal Structures and Optical Properties

Abstract2‐(2‐methoxyphenyl)benzoxazole (MBO) displays similar photophysical properties to 2‐(2‐hydroxyphenyl)benzoxazole (HBO), but it lacks the large Stokes shifts necessary for fluorescence microscopy applications. In this paper, we report the 5‐substitution of MBO with aryl groups to produce 2‐(4‐methoxy‐[1,1’‐biphenyl]‐3‐yl)benzoxazoles (MBBOs) with large Stokes shifts. The synthesis of MBBOs 6–15 was accomplished in moderate to good yields by microwave‐assisted Sonogashira cross couplings. Crystal structures for compounds 6–9 and 15 are provided. MBBOs 6–10, 12, and 14 displayed considerably blue‐shifted absorption maxima and slight bathochromic shifts of their fluorescence maxima relative to the unsubstituted MBO.

Facile synthesis of diiodoheteroindenes and understanding their Sonogashira cross-coupling selectivity for the construction of unsymmetrical enediynes.

Electrophile-promoted cyclizations of functionalized alkynes offer a useful tool for constructing halogen-substituted heterocycles primed for further derivatization. Preinstallation of an iodo-substituent at the alkyne prior to iodo-cyclization opens access to ortho di-iodinated heterocyclic precursors for the preparation of unsymmetrical heterocycle-fused enediynes. This general approach was used to prepare 2,3-diiodobenzothiophene, 2,3-diiodoindole, and 2,3-diiodobenzofuran, a useful family of substrates for systematic studies of the role of heteroatoms on the regioselectivity of cross-coupling reactions. Diiodobenzothiophene showed much higher regioselectivity for Sonogashira cross-coupling at C2 than diiodoindole and diiodobenzofuran. As a result, benzothiophene can be conveniently involved in a one-pot sequential coupling with two different alkynes, yielding unsymmetrical benzothiophene-fused enediynes. On the other hand, the Sonogashira reaction of diiodoindole and diiodobenzofuran formed considerable amounts of di-substituted enediynes in addition to the monoalkyne product by coupling at C2. Interestingly, no C3-monocoupling products were observed for all of the diiodides, suggesting that the incorporation of the 1st alkyne at C2 activates the C3 position for the 2nd coupling. Additional factors affecting regioselectivity were detected, discussed and connected, through computational analysis, to transmetalation being the rate-determining step for the Sonogashira reaction. Several enediynes synthesized showed cytotoxic activity, which is not associated with DNA strand breaks typical of natural enediyne antibiotics.

Synthesis of the methyl ester of 17(R/S)-Me-RvD5n-3 DPA and relief of postoperative pain in male mice.

The synthesis and biological evaluation of 17(R/S)-Me-RvD5n-3 DPA, an analog of the specialized pro-resolving mediators RvD5 and RvD5n-3 DPA, are presented. The synthesis was successfully accomplished utilizing Midland Alpine borane reduction, Sonogashira cross-coupling and a one-pot hydrozirconation/iodination protocol. In vivo evaluation of RvD5, RvD5n-3 DPA and 17(R/S)-Me-RvD5n-3 DPA in a mouse model of fracture revealed that all three compounds inhibited postoperative pain in male mice, but not in female mice.

NIR absorbing ferrocenyl perylenediimide-based donor-acceptor chromophores.

A set of ferrocenyl-functionalized perylenediimide (PDI) compounds and their 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) derivatives 1-5 were designed and synthesized using palladium-catalyzed Sonogashira cross-coupling, followed by a thermally activated [2 + 2] cycloaddition-retroelectrocyclization [CA-RE] reaction with a 1,1,2,2-tetracyanoethylene (TCNE) acceptor in good yields. The TCBD group works as an acceptor, whereas the ferrocenyl group acts as a donor at the central PDI core. The effects of varying the number of ferrocenyl and TCNE groups on the photophysical, thermal, electrochemical, and spectroelectrochemical properties were studied. The di-substituted PDI derivatives 3, 4, and 5 exhibit bathochromic shifts in the absorption spectra compared to 1 and 2, attributed to the extended π-conjugation. The electrochemical analysis of derivatives 2, 4, and 5 shows multiple reduction waves in the low potential region due to the presence of TCBD and perylenediimide acceptor units. Spectroelectrochemical studies were performed, showing that upon applying redox potentials, the absorption spectra shifted from the visible to the near-infrared (NIR) region. Computational calculations indicate that in the HOMO, the electron density is localized on the ferrocene unit, while in the LUMO, it is distributed over the PDI-TCBD unit, indicating a strong D-A interaction.

Desulfitative Sonogashira cross-coupling of thiopyronin for the synthesis of NIR arylacetylene-containing rhodamines.

A classical, safe and efficient red-shift strategy contributing to NIR arylacetylene-containing rhodamines has been developed via the desulfitative Sonogashira cross-coupling reaction of thiopyronin for the first time, exhibiting a broad substrate scope with good yields. In addition, compound 3m shows great potential for application as a singlet oxygen probe, demonstrating the practicality of the method.

Expanding the Frontier of Linear Drug Design: Cu-Catalyzed Csp -Csp 3 -Coupling of Electron-Deficient SF4 -Alkynes with Alkyl Iodides.

Despite the attractive properties of tetrafluorosulfanyl (SF4 ) compounds in drug discovery, medicinal research on SF4 molecules is hindered by the scarcity of suitable synthetic methodologies. Drawing inspiration from the well-established Sonogashira cross-coupling of terminal alkynes under Pd-catalysis, it is envisioned that SF4 -alkynes can serve as effective coupling partners. To overcome the challenges associated with the electron-deficient nature of SF4 -alkynes and the lability of the SF4 unit under transition-metal catalysis, an aryl radical mediated Csp -Csp 3 cross-coupling reaction is successfully developed under Cu catalysis. This methodology facilitates the coupling of SF4 -alkynes with alkyl iodides, leading to the immediate synthesis of SF4 -attached drug-like molecules. These findings highlight the potential impact of SF4 -containing molecules in the drug industry, paving the way for further research in this emerging field.

NIR-absorbing TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD bridged derivatives of 1,1′-bis(N,N-dimethylaniline)-substituted ferrocene

Symmetrical and unsymmetrical donor-acceptor (D–A) based chromophores were designed and synthesized by the Pd–catalyzed Sonogashira cross–coupling reaction of 1,1′-diiodoferrocene with (4-N,N-dimethylaminophenyl)ethyne followed by [2+2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). Ferrocene was used as a central donor unit and 4-(N,N-dimethylamino)phenyl group as the end-capping donor. Herein, we report the cycloaddition-retrocyclization reaction of TCNE/TCNQ groups on the disubstituted ferrocene containing more than one triple bond to get disubstituted tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD products. The effect of the conjugation length and different π–acceptor linkers were investigated by photophysical, redox and computational studies. The redox study reveals multiple oxidation waves corresponding to donor moieties (ferrocene and 4-(N,N-dimethylamino)phenyl group) and reduction waves corresponding to acceptor units (TCBD / cyclohexa-2,5- diene-1,4-diylidene-expanded TCBD). The thermogravimetric analysis data shows that the compounds exhibit high thermal stability. The computational studies reveal HOMO-LUMO gaps consistent with the experimentally obtained data.

Synthesis and antituberculosis activity of new 5-alkynyl derivatives of 2-thiouridine: application of new scaffold

We herein describe new potent inhibitors of mycobacteria based on 5-substituted 2-thiouridine derivatives. A series of new 5-alkynyl-substituted 2-thiouridine derivatives were synthesized via palladium-catalysed Sonogashira cross-coupling reaction of 5-iodo-2-thiopyrimidine base with terminal acetylenes with good yields in DMF at room temperature. It was found that sulfur atom in C2 position of pyrimidine ring had no impact on yields of target compounds. All obtained compounds were evaluated for their antimycobacterial activity against Mycobacetrium bovis and Mycobacterium tuberculosis at concentrations of 0.1-100 µg/ml using MABA test. Synthesized nucleosides showed high antimycobacterial activity against Mycobacterium bovis and Mycobacteri um tuberculosis. The obtained MIC50 values of 2-thionucleosides 14, 15 and 16 (0.28-0.75 µg/ml) significantly exceed characteristics of reference drug rifampicin, D-cycloserine and isoniazid, which gives prerequisites for further more detailed studies.

Synthesis and Antitubercular Activity of New 5-Alkynyl Derivatives of 2-Thiouridine

New efficient mycobacterial inhibitors based on 5-substituted 2-thiouridine derivatives have been described. A series of new 5-alkynyl-substituted 2-thiouridines have been synthesized in good yields by the palladium-catalyzed Sonogashira cross-coupling of 5-iodo-2-thiopyrimidine base with terminal alkynes in DMF at room temperature. The presence of a sulfur atm at C2 of the pyrimidine ring has been shown not to affect the yield of the target compounds. The synthesized 2-thiouridine derivatives were evaluated for their antimyco­bacterial activity against Mycobacterium bovis and Mycobacterium tuberculosis at concentrations of 0.1 to 100 μg/mL using microplate Alamar Blue assay (MABA). The compounds showed high antimycobacterial activity against both tested strains. The MIC50 values for 2-thionucleosides 14–16 (0.28–0.75 μg/mL) were much superior to those of the reference drugs rifampicin, D-cycloserine, and isoniazid, which makes these compounds promising for further more detailed study.

Copper- and Ligand-Free Sonogashira Cross-Coupling: Access to Novel 3-Aminoindole Derivatives and Their Biological Evaluations

Indole-containing compounds are widely distributed in the plant and animal kingdom, and their biological activity and pharmacological properties have prompted research into their chemical properties. This study developed a one-pot methodology for the synthesis of 3-aminoindole derivatives using copper- and ligand-free Sonogashira cross-coupling reaction conditions. The synthesised 3-aminoindole derivatives were confirmed using spectroscopic techniques. The resulting 3-aminoindole derivatives were biologically evaluated against Mycobacterium tuberculosis and Plasmodium falciparum. For example, indole derivatives 10a (7.813 µM) and 10j (8.332 µM) were the most active derivatives in the CAS and ADC media, respectively.

Recent Advances in Transition-Metal-Catalyzed Sonogashira Cross-Coupling Reactions of Alkyl Electrophiles

AbstractCatalytic Sonogashira cross-coupling reactions represent an efficient and versatile approach for constructing complex alkynes from readily available starting materials. Despite notable progress in this field, the development of transition-metal-catalyzed Sonogashira cross-coupling reactions of alkyl electrophiles remains limited. This limitation primarily stems from the low reactivity and pronounced propensity of these compounds towards β-H elimination. To overcome these challenges, researchers have investigated the use of palladium, nickel, and copper catalysts for Sonogashira reactions of alkyl electrophiles. Furthermore, significant strides have been made in achieving asymmetric Sonogashira cross-coupling reactions of electrophiles. This short review provides an overview of recent breakthroughs in this area.1 Introduction2 Palladium-Catalyzed Sonogashira Cross-Coupling of Alkyl Halides3 Nickel-Catalyzed Sonogashira Cross-Coupling of Alkyl Halides4 Copper-Catalyzed Sonogashira Cross-Coupling of Alkyl Electrophiles4.1 Copper-Catalyzed Racemic Sonogashira Cross-Coupling of Alkyl Electrophiles4.2 Copper-catalyzed Asymmetric Sonogashira Cross-Coupling of Alkyl Electrophiles5 Conclusions and Perspectives

NIR-Absorbing 1,1,4,4-Tetracyanobuta-1,3-diene- and Dicyanoquinodimethane-Functionalized Donor-Acceptor Phenothiazine Derivatives: Synthesis and Characterization.

A series of symmetrical and unsymmetrical donor-acceptor type phenothiazine derivatives 1-18 were designed and synthesized via Pd-catalyzed Sonogashira cross-coupling and [2 + 2] cycloaddition-retroelectrocyclization reactions. The incorporation of cyano-based acceptors 1,1,4,4-tetracyanobutadiene (TCBD) and dicyanoquinodimethane (DCNQ) in the phenothiazine derivatives resulted in systematic variation in the photophysical, thermal, and electrochemical properties. The electronic absorption spectra of the phenothiazine derivatives with strong acceptors 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 show red-shifted absorption as compared to phenothiazine derivatives 1, 4, 7, 10, 13, and 16 in the near-IR region due to a strong intramolecular charge transfer (ICT) transition. The electrochemical analysis of the phenothiazine derivatives 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 reveals two reduction waves at low potential due to the TCBD and DCNQ acceptors. The mono-TCBD-functionalized phenothiazine 2 shows higher thermal stability compared to other phenothiazine derivatives. The computational studies on phenothiazines 1-18 reveal the LUMO is substantially stabilized as acceptor strength increases, which lowers the HOMO-LUMO gap.

Development of Multivalent Conjugates with a Single Non-Canonical Amino Acid.

Proteins represent powerful biomacromolecules due to their unique functionality and broad utility both in the cell and in non-biological applications. The genetic encoding of non-canonical amino acids (ncAAs) facilitates functional diversification of these already powerful proteins. Specifically, ncAAs have been demonstrated to provide unique functional handles to bioorthogonally introduce novel functionality via conjugation reactions. Herein we examine the ability of a single ncAA to serve as a handle to generate multivalent bioconjugates to introduce two or more additional components to a protein, yielding a multivalent conjugate. To accomplish this aim, p-bromopropargyloxyphenyalanine (pBrPrF) was genetically encoded into both superfolder green fluorescent protein (sfGFP) and ubiquitin model proteins to serve as a conjugation handle. A sequential bioconjugation sequence involving a copper-assisted cycloaddition reaction coupled with a subsequent Sonogashira cross-coupling was then optimized. The linkage of two additional molecules to the model protein via these reactions yielded the desired multivalent bioconjugate. This domino approach using a single ncAA has a plethora of applications in both therapeutics and diagnostics as multiple unique moieties can be introduced into proteins in a highly controlled fashion.

Designing PdxCuy octahedra alloy nanocatalysts supported on solid substrates for solvent-free sonogashira cross-coupling reaction: Rational optimization of metal precursors

The current research details a scientific inquiry into an economic, reproducible, and adaptable synthetic process for the formation of PdxCuy octahedra (Oh) alloy nanocatalysts. Herein, several alloys such as Pd3Cu7, Pd4Cu6, Pd5Cu5, Pd6Cu4, and Pd7Cu3 are synthesized by altering the metal precursors quantities, resulting in a specific octahedral shape for all the ratios. After a thorough optimization study, Pd6Cu4 alloy was selected and anchored onto three solid substrates to achieve Pd6Cu4@hBNNs, Pd6Cu4@ZrO2 and Pd6Cu4@GONs nanocatalysts. Furthermore, the nanocatalysts were investigated for the Sonogashira cross-coupling reaction under solvent-free conditions, with the 15 wt% of the metal-support ratio of Pd6Cu4@hBNNs exhibiting remarkable catalytic activity when compared to the other two supported nanocatalysts. In advance, highly active Pd6Cu4@hBNNs nanocatalyst has many advantages, including mild reaction conditions, benign and minimum reaction duration. Moreover, the catalyst showed an efficient yield of 95 % for the model Sonogashira cross-coupling and considerable recyclability up to the 8th consecutive cycle achieving a 65 % yield. The outstanding performance of this economically viable nanocatalyst is most likely influenced by the synergistic effect of the catalyst and its strong metal-support contact.

Electroactive Dyes Based on 1,8-Naphthalimide with Acetylene Linkers as Promising OLED Materials - the Relationship Between Structure and Photophysical Properties.

Four A-π-D-π-A type small organic molecules with 1,8-naphthalimide motifs were successfully synthesised. The designed compounds are built of two 1,8-naphthalimide units linked via ethynyl π-linkages with selected functionalised donor motifs i. e. 2,2'-bithiophene, fluorene, phenothiazine and carbazole derivative. The synthesis based on Sonogashira cross-coupling allowed us to obtain the presented dyes with good yields. The resulting symmetrical small molecules' optical, electrochemical and thermal properties were thoroughly investigated, and their potential applicability for the OLED devices was demonstrated. In addition, the relationship between molecular structure and properties was considered by employing experimental and theoretical studies. As a result of using various donor groups, it was possible to achieve efficient electroluminescence in the range from green (DEV4) to orange-red light (DEV3) with a maximum luminance of 3 820 cd/m2 for DEV4. Upon the insertion of an acetylene linker to the designed molecules, the free rotation of D and A fragments, and hence the effective π-electron communication within the entire molecule, is possible, which was confirmed by DFT studies. The obtained dyes are characterised by high thermal stability, reversible oxidation-reduction process, satisfactory optoelectronic properties and good solubility in organic solvents, which is advisable for the application in small molecular organic light-emitting diodes (SM-OLEDs) technology.