Aromatic Alkynes Research Articles

Synthesis of flower-shaped cyclodextrin microporous organic networks for selective recovery of acetophenone and 1-phenylethanol from petrochemical effluents

Fabrication of efficient and renewable biomass-derivatives-based porous materials with large surface area, good stability and selectivity for recovering acetophenone (AP) and 1-phenylethanol (PE) from petrochemical by-products is of great significance and challenge. In this work, nine novel cyclodextrins-based microporous organic networks (CD-MONs) are designed and synthesized by choosing various CD-based building blocks and aromatic alkynes. Among them, a flower-shaped DEB-γ-CD-MON not only retains the cage-type cavity and the high density of hydroxyl sites within γ-CD, possesses the large surface area, outstanding chemical robustness and strong hydrophobicity, but also offers high AP adsorption capacity (1.93 mmol g−1), good AP/PE selectivity (8.1), and recycle stability both in batch and continuous adsorption modes. The experimental and theoretical results indicate that the hydrogen bonding, π-π stacking and van der Waals interaction between adsorbents and adsorbates are favorable for binding AP toward PE. This work not only provides a biomass-derivatives-based adsorbent for the separation and recovery of AP and PE from PO/SM waste effluent, but also breaks the limitation of the original structure and characteristic of natural biomass to realize added value in biomass valorization.

Photocatalytic Terminal C-C Coupling Reaction Inside Water Soluble Nanocages.

Developing methods that activate C-H bonds directly with high selectivity for C-C bond formation in complex organic synthesis has been a major chemistry challenge. Recently it has been shown that photoactivation of weakly polarized C-H bonds can be carried out inside a cationic water-soluble nanocage with visible light-mediated host-guest charge transfer (CT) chemistry. Using this novel photoredox activation paradigm, here we demonstrate C-C bond formation to photo-generate 1,3-diynes at room temperature in water from terminal aromatic alkynes for the first time. The formation of cavity-confined alkyne radical cation and the proton-removed neutral radical species highlight the unique C-C coupling step driven by supramolecular preorganization.

Photocatalytic Terminal C−C Coupling Reaction Inside Water Soluble Nanocages

AbstractDeveloping methods that activate C−H bonds directly with high selectivity for C−C bond formation in complex organic synthesis has been a major chemistry challenge. Recently it has been shown that photoactivation of weakly polarized C−H bonds can be carried out inside a cationic water‐soluble nanocage with visible light‐mediated host‐guest charge transfer (CT) chemistry. Using this novel photoredox activation paradigm, here we demonstrate C−C bond formation to photo‐generate 1,3‐diynes at room temperature in water from terminal aromatic alkynes for the first time. The formation of cavity‐confined alkyne radical cation and the proton‐removed neutral radical species highlight the unique C−C coupling step driven by supramolecular preorganization.

Click synthesis and self-assembly of novel dendritic ethylene glycol/alkyl-substituted diarylated triazoles into supramolecular nanofibers

Copper-catalyzed 1, 3-dipolar cycloaddition reaction between azides and alkynes under mild conditions has been known to exhibit high selectivity and good yields of 1, 2, 3-triazole. Additionally, 1, 2, 3-triazoles are used in various medical and pharmaceutical applications. Herein, we present novel low molecular weight organogelators from fluorescent ethylene glycol/alkyl-substituted 2, 6-diarylated pyridine 1, 2, 3-triazoles. Compact supramolecular architectures were created by the self-assembly of the synthesized gelators. The gel formation activity of the prepared ethylene glycol/alkyl-substituted 2, 6-diarylated pyridine triazoles were presented. The synthesis process was achieved by copper-catalyzed alkyne-azide cycloaddition (CuAAC) of ethylene glycol/alkyl-functionalized aromatic azide with aromatic alkyne bearing alkyl ester tails of various lengths. The ethylene glycol/alkyl-functionalized diaryl triazoles were investigated by 1H/13C NMR and FTIR spectroscopic methods. Triazoles with long ethylene glycol and/or alkyl ester tails showed an enhanced gelation activity as compared to those with shorter ethylene glycol and/or alkyl ester tails. The morphological features of the self-assembled ethylene glycol/alkyl-substituted arylated triazoles were studied by scanning electron microscopy (SEM), demonstrating supramolecular nanofibrous assemblies. Those supramolecular assemblies were forced by van der Waals and π-stacks interactions. Both antibacterial activity and cytotoxicity of the synthesized arylated triazole gelators were studied.

Cobalt nanoparticles-catalyzed aerobic oxygenation and esterification of alkynes via C≡C bonds cleavage

An unprecedented efficient protocol is developed for the oxidative cleavage of C≡C bonds in alkynes to produce structure-diverse esters using heterogeneous cobalt nanoparticles as catalyst with molecular oxygen as the oxidant. A diverse set of mono- and multisubstituted aromatic and aliphatic alkynes can be effectively cleaved and converted into the corresponding esters. Characterization analysis and control experiments indicate high surface area and pore volume, as well as nanostructured nitrogen-doped graphene-layer coated cobalt nanoparticles are possibly responsible for excellent catalytic activity. Mechanistic studies reveal that ketones derived from alkynes under oxidative conditions are formed as intermediates, which subsequently are converted to esters through a tandem sequential process. The catalyst can be recycled up to five times without significant loss of activity.

Tröger's base derived 3D-porous aromatic frameworks with efficient exciton dissociation and well-defined reactive site for near-unity selectivity of CO2 photo-conversion

The overall photocatalytic conversion of CO2 and H2O to fuel and O2 is challenging. In this study, a series of three-dimensional Tröger's base-derived porous aromatic frameworks (3D-X-TB-PAFs (X = TEPE, TEPM, SPF)) featuring designated reaction sites and unique charge transfer properties were developed. The incorporation of V-shaped Tröger's base (TB) units and aromatic alkynes imparts the polymers with permanent porosity, additional photon scattering cross-sections, and enhanced CO2 adsorption/activation capabilities. Density functional theory calculations and optoelectronic measurements revealed the formation of intramolecular built-in polarization and electron-trap sites induced by TB, which modulated charge separation and customized reaction sites in collaboration with 3D networks. In addition, product allocation during the photoreduction of CO2 was regulated by the photooxidation of H2O. Among the as-prepared 3D-PAFs, the most efficient electron transport channel was demonstrated by the TEPE-TB-PAF with fully conjugated TEPE-T. In the absence of cocatalysts and sacrificial agents, TEPE-TB-PAF exhibits a competitive CO formation rate (194.50 μmol g−1 h−1) with near-unity selectivity (99.74%). Significantly, the low energy barrier for CO desorption and the high energy barrier for *CHO formation contribute to the high efficiency of TEPE-TB-PAF, as demonstrated by computational exploration and in situ diffuse reflectance infrared Fourier transform spectra. This work offers efficient building blocks for the synthesis of multifunctional organic photocatalysts and groundbreaking insights into the simultaneous enhancement of photocatalytic reactivity and selectivity.

A general palladium‐catalyzed carbonylation synthesis of aurones with aryl bromides using CO2

AbstractA general and efficient strategy synthesis of aurones by carbonylation reaction of aryl bromides and terminal aromatic alkynes using CO2 has been established. Various terminal aromatic alkynes and 2‐bromophenol by using CO2 with hydrosilane could be leveraged to provide various aurones in good yields under mild reaction conditions. Moreover, palladium‐catalyzed carbonylation reaction mechanism is proposed for the preparation of aurones.

A Simple and Practical Bis-N-Heterocyclic Carbene as an Efficient Ligand in Cu-Catalyzed Glaser Reaction.

Conjugated diyne derivatives are important scaffolds in modern organic synthetic chemistry. Using the Glaser reaction involves the coupling of terminal alkynes which can efficiently produce conjugated diyne derivatives, while the use of a stoichiometric amount of copper salts, strong inorganic base, and excess oxidants is generally needed. Developing an environmentally friendly and effective method for the construction of symmetrical 1,3-diynes compounds by Glaser coupling is still highly desirable. In this study, we present an economical method for the production of symmetric diynes starting from various terminal acetylenes in a Glaser reaction. A simple and practical bis-N-heterocyclic carbene ligand has been introduced as efficient ligands for the Cu-catalyzed Glaser reaction. High product yields were obtained at 100 °C for a variety of substrates including aliphatic and aromatic terminal alkynes and differently substituted terminal alkynes including the highly sterically hindered substrate 2-methoxy ethynylbenzene or 2-trifluoromethyl ethynylbenzene and a series of functional groups, such as trifluoromethyl group, ester group, carboxyl group, and nitrile group. The established protocol is carried out in air under base-free condition and is operationally simple. These research work suggest that bis-N-heterocyclic carbene could also an appealing ligand for Glaser reaction and provide a reference for the preparation of symmetric 1,3-diynes in industrial filed.

Micelle-Mediated Sonogashira Coupling for DNA-Encoded Library Synthesis.

DNA-Encoded Libraries (DELs) are becoming widely established as a hit identification strategy for drug discovery campaigns. Their successful application relies on the availability and efficiency of the reactions that can be carried out on DNA. These reactions should proceed with high conversion to the desired product and have a broad substrate scope to synthesise chemically diverse and drug-like DELs. The Sonogashira coupling provides a unique means of coupling an sp-hybridized carbon centre to an aryl halide and methods to achieve this reaction on DNA are highly desirable. We report the application of our micellar technology for on-DNA chemistry to the Sonogashira reaction. This method gives highly efficient conversions for the coupling of (hetero)aromatic and aliphatic alkynes to (hetero)aryl iodides and bromides allowing the preparation of highly diverse DELs.

Gold-catalyzed four-component multifunctionalization of alkynes

The alkyne unit is a versatile building block in organic synthesis and the development of selective multifunctionalization of alkynes is an important object of research in this field. Herein, we report an interesting gold-catalyzed, four-component reaction that achieves the oxo-arylfluorination or oxo-arylalkenylation of internal aromatic or aliphatic alkynes, efficiently breaking a carbon-carbon triple bond and forming four new chemical bonds. The reaction divergence can be controlled by site-directing functional groups in the alkynes; the presence of a phosphonate unit favors the oxo-arylfluorination, while the carboxylate motif benefits oxo-arylalkenylation. This reaction is enabled by an Au(I)/Au(III) redox coupling process using Selectfluor as both an oxidant and a fluorinating reagent. A wide range of structurally diverse α,α-disubstituted ketones, and tri- or tetra-substituted unsaturated ketones have been prepared in synthetically valuable yields and with excellent chemo-, regio- and stereoselectivity. The gram-scale preparation and late-stage application of complex alkynes have further enhanced their synthetic value.

A novel nanomagnetic palladium (II) complex of bisimidazolium-based N[sbnd]heterocyclic carbene; An efficient heterogeneous catalyst for A3 coupling reactions

Herein, a novel nanomagnetic NHC-Palladium complex was successfully prepared applying post-synthetic modification (PSM) condensation between Fe3O4-support imidazole and a synthetic bisamide moiety, carrying the alkyl halide functionalities at the end of its chain, followed by chelation of Pd ions to generate the corresponding complex. The [Fe3O4@bisimidazolium-Pd]2Cl− complex gave the best catalytic performance in synthesizing propargylamines through A3 coupling of various substituted aromatic and cycloaliphatic aldehydes and secondary amines with aromatic and liner alkynes in PEG-400. Primary amines are inefficient to produce unknown byproducts; whereas, secondary amines react quickly. Significantly, alkynes having a high electron density reduce the conversion rate. Moreover, aromatic and aliphatic aldehydes are active, but the electron-drawing substituent on benzaldehyde decreases the rate of conversion. Furthermore, the [Fe3O4@bisimidazolium-Pd]2Cl− catalyst can be reused seven times without metal leaching or losing its ability, which shows how stable it is when used in a reaction.

Direct Access to α,β-Alkynylamides via Pd-Catalyzed Carbonylation of Terminal Alkynes with Amines Using Chloroform as the CO Surrogate.

We describe the first-time use of a palladium-di(1-adamantyl)-n-butylphosphine catalytic system for the synthesis of alk-2-ynamides from terminal alkynes via aminocarbonylation reaction. This method avoids the direct use of toxic CO gas by utilizing chloroform as an in situ CO source. The aminocarbonylation of both aromatic and aliphatic electron-rich alkyne nucleophiles is reported for the first time. The mild condition provides alk-2-ynamides within 50 min under microwave irradiation at 80 °C.

CuBr2@g-C3N4-catalyzed cyclization of aromatic alkyne ketones to obtain indenones with K2S2O8 under blue light irradiation

We developed a new scheme of preparing indenones by cyclization of aromatic alkyne ketones based on an admixture of photocatalysts CuBr2@g-C3N4. Also, benzoylindenone was obtained in the yield of 95.2% under blue light at room temperature. By screening the experimental conditions, the mechanism of CuBr2@g-C3N4 catalyzed aryl cyclization was the formation of cyclic 1H-inden-1-one compounds by the generation of transfer electrons excited under blue light. According to the goal of sustainable development of green chemistry, an economical method for preparing indenone from aromatic alkyne ketone was proposed by our team.

Dehydroborylation of Terminal Alkynes Using Lithium Aminoborohydrides.

Dehydrogenative borylation of terminal alkynes has recently emerged as an atom-economical one-step alternative to traditional alkyne borylation methodologies. Using lithium aminoborohydrides, formed in situ from the corresponding amine-boranes and n-butyllithium, a variety of aromatic and aliphatic terminal alkyne substrates were successfully borylated in high yield. The potential to form mono-, di-, and tri-B-alkynylated products has been shown, though the mono-product is primarily generated using the presented condition. The reaction has been demonstrated at large (up to 50 mmol) scale, and the products are stable to column chromatography as well as acidic and basic aqueous conditions. Alternately, the dehydroborylation can be achieved by treating alkynyllithiums with amine-boranes. In that respect, aldehydes can act as starting materials by conversion to the 1,1-dibromoolefin and in situ rearrangement to the lithium acetylide.

Harnessing Protonated 2,2'-Bipyridinium Salts as Powerful Brønsted Acid Catalysts in Organic Reactions.

It is the first time that the readily available protonated 2,2'-bipyridinium salts are used as Brønsted acid catalysts to accelerate a series of organic transformations that included the hydration of aromatic alkynes, etherification of alcohols, cyclotrimerization of aliphatic aldehydes, Ritter reaction, Mannich reaction, Biginelli reaction, preparation of substituted alkenes from alcohols, synthesis of spirooxindole, bisindolylmethane, and noncyclized tetraketone with good to excellent yields. These results strongly suggest that there exists enormous potentiality in the development of the protonated 2,2'-bipyridinium catalytic system.

Palladium-Catalyzed Carbonylation for General Synthesis of Aurones Using CO2.

The carbonylation of alkynes using CO2 to generate aurones is to date unknown. In this study, a palladium-catalyzed carbonylation of terminal aromatic alkynes and the waste hydrosilane, poly(methylhydrosiloxane) (PMHS), is carried out with 2-iodophenol using CO2 to produce aurones. A variety of terminal alkynes and substituted 2-iodophenols are transformed into aurones in good yields. Preliminary mechanistic studies indicate that silyl formate, generated from CO2 and PMHS, plays a crucial role in the carbonylation reaction.

Palladium-catalyzed Sonogashira coupling to synthesis of gem‑difluoroenynes

Herein, we developed the palladium-catalyzed Sonogashira-type cross-coupling of 1‑bromo-2,2-difluoroethylene with a variety of aromatic and aliphatic terminal alkynes proceeds smoothly at mild reaction condition to access the corresponding gem‑difluoroenyne derivatives. 1-Bromo-2,2-difluoroethylene is a useful difluoroethenyl source because of its commercially available and easy-to-handle. This new synthetic protocol provided a novel strategy to directly construct gem‑difluoroenynes with good functional group tolerance and high yields.

CeO2‐Nanorods‐Catalyzed Protoboration of Alkenes and Alkynes with Bis(pinacolato)diboron

AbstractThe protoboration of alkenes and alkynes with B2pin2 (pin=OCMe2CMe2O) using a heterogeneous CeO2 nanorods catalyst has been developed to afford the corresponding alkyl and vinyl boronate esters in 41–99% yield under mild reaction conditions. A series of aromatic and aliphatic alkenes and alkynes with synthetically important functional groups were well tolerated. In both the systems, the catalyst could be reused for up to six runs without significant loss in activity. Stoichiometric reactions revealed that the protoboration may proceed through the in situ formed catalytically active boryl species.magnified image

Novel pH-sensitive catechol dyes synthesised by a three component one-pot reaction.

The synthesis and characterisation of new dyes based on indolizines bearing catechol groups in their structure is presented. The preparation was carried out through a simple three component one-pot reaction promoted by CuNPs/C, between pyridine-2-carbaldehyde, an aromatic alkyne and a tetrahydroisoquinoline (THIQ) functionalized with catechol groups. The products were isolated in 30%-34% yield, which was considered more than acceptable considering that the catechol hydroxyl groups were not protected prior to reaction. In view of the colour developed by the products and their response to the acidic and basic conditions of the medium, product 3aa was studied by UV-Vis and NMR spectroscopies at different pH values. We concluded that product 3aa suffered two deprotonations at pKa of 4.4 and 9.5, giving three species in a pH range between 2-12, with colours varying from light red to deep orange. The reversibility of the process observed for 3aa at different pH values, together with its changes in colour, make this new family of products attractive candidates to use them as pH indicators.

Applications of sulfonyl hydrazides in radical cyclization of alkenes.

Radical cyclization is regarded as a powerful and promising strategy for the assembly of diverse important cyclic structures because of its high atom- and step-economy. As excellent radical acceptors, alkenes offer two potential directions, pushing the research domain of radical cyclization. In this context, as a radical precursor, sulfonyl hydrazide plays an important role in accomplishing radical cyclization of alkenes in a facile and efficient way. This review focuses on the applications of sulfonyl hydrazides in radical cyclization of alkenes, which generally has two radical conversion modes, sulfonyl radicals and sulfoxide radicals. In particular, the section of sulfonyl radicals consists of eight parts containing aromatic rings, alkenes, alkynes, cyanides, aldehydes, carboxylic acids, amides, and small ring compounds, according to the objects of cyclization after addition with alkenes. Within each category, representative instances are presented and discussed in terms of their general mechanistic perspectives when needed.