Synthesis of Naturally Occurring Polyynes

Expedient synthesis of conjugated triynes via alkyne metathesis

The first synthesis of conjugated triynes by molybdenum-catalysed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site-selective alkyne metathesis to produce the desired conjugated triyne products. The steric hindrance of the alkyne moiety was found to be crucial in preventing the formation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity.

The first synthesis of symmetrical and dissymmetrical conjugated triynes by self- and cross-metathesis was successfully achieved thanks to the use of hindered diynes.

Ligand and additive free aerobic synthesis of diynes using Pd–CuFe2O4magnetic nanoparticles as an efficient reusable catalyst

Herein, we present the synthesis of Pd–CuFe₂O₄magnetic nanoparticles as an efficient and recyclable catalyst for the oxidative homocoupling of various terminal alkynes to form symmetric 1,3-diynes.

Phosphine-catalyzed [3 + 2] cycloadditions of trifluoromethyl enynes/enediynes with allenoates: access to cyclopentenes containing a CF3-substituted quaternary carbon center

The first use of trifluoromethyl-substituted enynes/enediynes as non-classical electron-deficient olefins for phosphine-catalyzed [3 + 2] cycloaddition with allenoates is presented.

Cu2O polyhedra for aryl alkyne homocoupling reactions

Cu₂O rhombic dodecahedra display good catalytic activities toward diverse aryl alkyne homocoupling reactions.

Solvent-dependent termination, size and stability in polyynes synthesized via laser ablation in liquids

UV-vis and SERS spectroscopy reveal the solvent effect on termination, size and stability in polyynes synthesized via laser ablation in liquids.

Sulphonic acid functionalized porphyrin anchored with a meso-substituted triazolium ionic liquid moiety: a heterogeneous photo-catalyst for metal/base free C–C cross-coupling and C–N/C–H activation using aryl chloride under visible light irradiation

We report an easy process to synthesize sulphonic acid functionalized porphyrin with meso-substituted triazolium ionic liquid moiety for metal/base free C–C cross-coupling and C–N/C–H activation using aryl chloride under visible light irradiation.

Investigations into the mechanism of copper-mediated Glaser-Hay couplings using electrochemical techniques

The mechanism of the copper mediated C-C bond forming reaction known as Glaser-Hay coupling (alkyne dimerization) has been investigated using electrochemical techniques. Applying an oxidative potential to a copper or copper-coated graphite electrode in the presence of the organic base DABCO results in the dimerization of phenylacetylene in good yield. Further mechanistic investigation has shown that this reaction medium results in the assembly of a dinuclear Cu(i) complex which, although previously reported, has never been shown to have catalytic properties for C-C bond formation. The complex is reminiscent of that proposed in the Bohlmann model for the Glaser-Hay reaction and as such lends weight to this proposed mechanism above the alternative proposed mononuclear catalytic cycle.

Study of Iron Gall Inks, Ingredients and Paper Composition Using Non-Destructive Techniques

Old manuscripts are among the most important elements of the cultural and historical heritage of ancient knowledge. Unfortunately, many of them suffer from degradation, mostly those written with iron gall inks. In the present work, a study using non-destructive techniques was designed with the aim of analyzing the elemental composition and structural characteristics of iron gall inks, reproduced in laboratory, paper and their interaction when the ink is deposited on paper, inducing the paper degradation. Proton induced X-ray emission, X-ray diffraction and Fourier-transform infrared spectroscopy provided the elemental and structural information, and photography under infrared (IR) and ultraviolet (UV) light allowed the differentiation between manufactured inks. Results show that the first step of inked paper deterioration is due to acid-hydrolysis of the cellulose and the presence of reactive Fe(II) species by reducing the crystallinity index of the paper, which is affected depending on the ink recipe and the starting raw materials. These results will be useful to future studies on ancient documents written with iron gall inks, which suffer deterioration due to ink corrosion, and to differentiate between the different paper degradation mechanisms.

Palladium-Catalyzed Decarboxylative Alkynylation of α-Acyloxyketones by C(sp3 )-O Bond Cleavage

Palladium-catalyzed decarboxylative alkynylation of α-acyloxyketones triggered by C(sp³ )-O bond cleavage is disclosed. The decarboxylation strategy featuring a neutral reaction condition enabled an unprecedent catalytic alkynylation of a ketone enolate. The reaction was applied to a variety of substrates, giving desired products in good yields. We successfully obtained X-ray crystallography of a new palladium-enolate intermediate that was synthesized by a reaction of [Pd(cod)(CH₂ TMS)₂ ] with XPhos and α-acyloxyketone at room temperature, indicating facile C(sp³ )-O bond disconnection.

Benzotriazole as an Efficient Ligand in Cu-Catalyzed Glaser Reaction

Benzotriazole has been established as an efficient ligand in Cu-catalyzed cross-coupling of terminal alkynes to form 1,3-dialkynes using CuI as the catalyst and K2CO3 as the base at room temperature in an open round-bottom flask. The established protocol has the following notable advantages: simple to handle, easy work-up, mild reaction condition, high substrate scope, requirement of less quantity of ligand and also Cu-catalyst, less expensive, and high reaction yield.

General Immobilization of Ultrafine Alloyed Nanoparticles within Metal-Organic Frameworks with High Loadings for Advanced Synergetic Catalysis

The development of a general synthesis approach for creating fine alloyed nanoparticles (NPs) in the pores of metal-organic frameworks (MOFs) shows great promise for advanced synergetic catalysis but has not been realized so far. Herein, for the first time we proposed a facile and general strategy to immobilize ultrafine alloyed NPs within the pores of an MOF by the galvanic replacement of transition-metal NPs (e.g., Cu, Co, and Ni) with noble-metal ions (e.g., Pd, Ru, and Pt) under high-intensity ultrasound irradiation. Nine types of bimetallic alloyed NPs of base and noble metals were successfully prepared and immobilized in the pores of MIL-101 as a model host, which showed highly dispersed and well-alloyed properties with average particle sizes ranging from 1.1 to 2.2 nm and high loadings of up to 10.4 wt %. Benefiting from the ultrafine particle size and high dispersity of Cu-Pd NPs and especially the positive synergy between Cu and Pd metals, the optimized Cu-Pd@MIL-101 exhibited an extremely high activity for the homocoupling reaction of phenylacetylene under unprecedented base- and additive-free conditions and room temperature, affording at least 19 times higher yield (98%) of 1,4-diphenylbuta-1,3-diyne than its monometallic counterparts. This general strategy for preparing various MOF-immobilized alloyed NPs potentially paves the way for the development of highly active metal catalysts for a variety of reactions.

Computational study on the 1,3-diyne synthesis from gold(i)-catalyzed alkynylation of terminal alkynes with alkynyl hypervalent iodine reagents under the aid of a silver complex and 1,10-phenanthroline

DFT calculations reveal a new Au/Ag co-catalyzed π-activation mechanism for the formation of unsymmetrical 1,3-diyne.

Fluorinated analogues of lipidic dialkynylcarbinol pharmacophores: synthesis and cytotoxicity in HCT116 cancer cells

Lipidic alkynylcarbinols (LACs) have been identified as potential antitumor compounds, and a thorough understanding of their pharmacophoric environment is now required to elucidate their biological mode of action. In the dialkynylcarbinol (DAC) series, a specific study of the pharmacophore potential has been undertaken by focusing on the synthesis of three fluorinated derivatives followed by their biological evaluation. This work highlights the requirement of an electron-rich secondary carbinol center as a key structure for cytotoxicity in HCT116 cells.

Recent trends and applications of the Cadiot–Chodkiewicz reaction

The Cadiot–Chodkiewicz reaction offers an elegant strategy for the formation of 1,3-diynes via Cu-catalyzed cross-coupling of alkynyl halides with terminal alkynes in the presence of an amine.

Selective synthesis of iridium(iii) end-capped polyynes by oxidative addition of 1-iodopolyynes to Vaska's complex

The reaction of bis(triphenylphosphine)iridium(i) carbonyl chloride (Vaska's complex) with a series of 1-iodopolyynes (1-C_nI and 2-C_nI) gave σ-polyynyl iridium(iii) complexes with general formula R(C[triple bond, length as m-dash]C)_nIr(PPh₃)₂(Cl)(I)(CO). The use of acetonitrile as a solvent appeared crucial and allowed selectively obtaining only one from a few possible isomers. The X-ray single crystal diffraction experiment for 2-C₄[Ir]I allowed the determination of the exact structure of this complex. Further spectroscopic measurements, especially ³¹P NMR, confirmed the formation of the same type of isomers with trans coordinated phosphines in each case. All complexes were fully characterized with the use of NMR (¹H, ¹³C and ³¹P), IR, UV/Vis, cyclic voltammetry and (ESI)HRMS techniques. Moreover, DFT calculations were performed for all the resulting species. The complexes with a linear carbon chain from butadiyne to decapentayne are the longest iridium end-capped polyynes known to date since only compounds with a (C[triple bond, length as m-dash]C)₂ structural motif have been reported so far. Moreover, we confirmed that the synthetic approach, first used for palladium(ii) end-capped polyynes, may be also applied for the synthesis of other structurally new organometallic polyynes.

Well-Defined Alkyne Metathesis Catalysts: Developments and Recent Applications

Although alkyne metathesis has been known for 50 years, rapid progress in this field has mostly occurred during the last two decades. In this article, the development of several highly efficient and thoroughly studied alkyne metathesis catalysts is reviewed, which includes novel well-defined, in situ formed and heterogeneous systems. Various alkyne metathesis methodologies, including alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), cyclooligomerization, acyclic diyne metathesis polymerization (ADIMET), and ring-opening alkyne metathesis polymerization (ROAMP), are presented, and their application in natural product synthesis, materials science as well as supramolecular and polymer chemistry is discussed. Recent progress in the metathesis of diynes is also summarized, which gave rise to new methods such as ring-closing diyne metathesis (RCDM) and diyne cross-metathesis (DYCM).

Transition metal-free coupling of terminal alkynes and hypervalent iodine-based alkyne-transfer reagents to access unsymmetrical 1,3-diynes

A variety of unsymmetrical 1,3-diynes can easily be accessed in good yields under catalyst- and transition metal-free conditions by reacting terminal alkynes with hypervalent iodine-based electrophilic alkyne-transfer reagents.

CuAAC click chemistry for the enhanced detection of novel alkyne-based natural product toxins

In the context of discovering and quantifying terminal alkyne-based natural products, here we report the combination of CuAAC click chemistry with LC-MS for the detection of polyether toxins (prymnesins) associated with harmful algal blooms. The added-value of the CuAAC-based approach is evident from our ability to detect novel prymnesin-like compounds in algal species with previously uncharacterised toxins.

Synthesis of 1,3-Diynes via Cadiot-Chodkiewicz Coupling of Volatile, in Situ Generated Bromoalkynes

A convenient Cadiot-Chodkiewicz protocol that facilitates the use of low molecular weight alkyne coupling partners is described. The method entails an in situ elimination from a dibromoolefin precursor and immediate subjection to copper-catalyzed conditions, circumventing the hazards of volatile brominated alkynes. The scope of this method is described, and the internal 1,3-diyne products are preliminarily evaluated in ruthenium-catalyzed azide-alkyne cycloadditions.

Oplopanax horridus: Phytochemistry and Pharmacological Diversity and Structure-Activity Relationship on Anticancer Effects

Oplopanax horridus, well-known as Devil's club, is probably the most important ethnobotanical to most indigenous people living in the Pacific Northwest of North America. Compared with the long history of traditional use and widespread distribution in North America, the study of O. horridus is relatively limited. In the past decade, some exciting advances have been presented on the phytochemistry and pharmacological diversity and structure-activity relationship on anticancer effects of O. horridus. To date, no systematic review has been drafted on the recent advances of O. horridus. In this review, the different phytochemicals in O. horridus are compiled, including purified compounds and volatile components. Animal and in vitro studies are also described and discussed. Especially, the potential structural-activity relationship of polyynes on anticancer effects is highlighted. This review aimed to provide comprehensive and useful information for researching O. horridus and finding potential agents in drug discovery.

Stereoselective total synthesis and structural revision of the diacetylenic diol natural products strongylodiols H and I

The stereoselective total synthesis of strongylodiol H and I has been accomplished. The synthetic procedure comprised the stereoselective reduction of a ketone functionality in an ene-yne-one employing CBS as a catalyst and a Cadiot-Chodkiewicz coupling reaction as the key reaction steps. A common aldehyde intermediate has been used for the synthesis of both strongylodiols.

Extraction of Linear Carbon Chains Unravels the Role of the Carbon Nanotube Host

Linear carbon chains (LCCs) have been shown to grow inside double-walled carbon nanotubes (DWCNTs), but isolating them from this hosting material represents one of the most challenging tasks toward applications. Herein we report the extraction and separation of LCCs inside single-walled carbon nanotubes (LCCs@SWCNTs) extracted from a double-walled host LCCs@DWCNTs by applying a combined tip-ultrasonic and density gradient ultracentrifugation (DGU) process. High-resolution transmission electron microscopy, optical absorption, and Raman spectroscopy show that not only short LCCs but clearly long LCCs (LLCCs) can be extracted and separated from the host. Moreover, the LLCCs can even be condensed by DGU. The Raman spectral frequency of LCCs remains almost unchanged regardless of the presence of the outer tube of the DWCNTs. This suggests that the major importance of the outer tubes is making the whole synthesis viable. We have also been able to observe the interaction between the LCCs and the inner tubes of DWCNTs, playing a major role in modifying the optical properties of LCCs. Our extraction method suggests the possibility toward the complete isolation of LCCs from CNTs.

Acetylenotrophy: a hidden but ubiquitous microbial metabolism?

Acetylene (IUPAC name: ethyne) is a colorless, gaseous hydrocarbon, composed of two triple bonded carbon atoms attached to hydrogens (C2H2). When microbiologists and biogeochemists think of acetylene, they immediately think of its use as an inhibitory compound of certain microbial processes and a tracer for nitrogen fixation. However, what is less widely known is that anaerobic and aerobic microorganisms can degrade acetylene, using it as a sole carbon and energy source and providing the basis of a microbial food web. Here, we review what is known about acetylene degrading organisms and introduce the term 'acetylenotrophs' to refer to the microorganisms that carry out this metabolic pathway. In addition, we review the known environmental sources of acetylene and postulate the presence of an hidden acetylene cycle. The abundance of bacteria capable of using acetylene and other alkynes as an energy and carbon source suggests that there are energy cycles present in the environment that are driven by acetylene and alkyne production and consumption that are isolated from atmospheric exchange. Acetylenotrophs may have developed to leverage the relatively high concentrations of acetylene in the pre-Cambrian atmosphere, evolving later to survive in specialized niches where acetylene and other alkynes were produced.

Skeletal Optimization of Cytotoxic Lipidic Dialkynylcarbinols

In line with a recent study of the pharmacological potential of bioinspired synthetic acetylenic lipids, after identification of the terminal dialkynylcarbinol (DAC) and butadiynyl alkynylcarbinol (BAC) moieties as functional antitumor pharmacophoric units, this work specifically addresses the issue of carbon backbone length. A systematic variation of the aliphatic chain length was thus carried out in both the DAC and BAC series. The critical impact of the length of the lipidic skeleton was first confirmed in the racemic series, with the highest cytotoxic activity observed for C₁₇ to C₁₈ backbones. Enantiomerically enriched samples were prepared by asymmetric synthesis of the optimal C₁₈ DAC and C₁₇ BAC derivatives. Samples with upgraded enantiomeric purity were alternatively produced by enzymatic kinetic resolution. Eutomers possessing the S configuration displayed cytotoxicity IC₅₀ values as low as 15 nm against HCT116 cancer cells, the highest level of activity reached to date in this series.

An Efficient Heterogeneous Palladium(0)-Catalysed Cross-Coupling between 1-Bromoalkynes and Terminal Alkynes Leading to Unsymmetrical 1,3-Diynes

An efficient heterogeneous palladium(0)-catalysed cross-coupling of 1-bromoalkynes with terminal alkynes was achieved in DMF at room temperature in the presence of 5 mol% of MCM-41-immobilised bidentate phosphine palladium(0) complex [MCM-41-2P-Pd(0)] and 2 mol% of CuI with Et3N as base, yielding a variety of unsymmetrical 1,3-diynes in moderate to good yields. This heterogeneous palladium(0) complex could be easily recovered by a simple filtration of the reaction solution and recycled at least seven times without significant decrease in activity.

Most favorable cumulenic structures in iron-capped linear carbon chains are short singlet odd-carbon dications: a theoretical view

DFT computations suggest that the odd iron-capped linear-carbon dications exhibit large ΔE_S–T values and more cumulenic structures than short even-carbon chains.

Alkyne-Substituted Fimbrolide Analogues as Novel Bacterial Quorum-Sensing Inhibitors

Gram-negative bacteria such as Pseudomonas aeruginosa use furanosyl diesters as autoinducers for quorum sensing (QS), a major regulatory and cell-to-cell communication system for social adaptation, virulence factor production, biofilm formation, and antibiotic resistance. A range of natural and synthetic brominated furanones, i.e. fimbrolide derivatives, have been found to act as inhibitors of QS-dependent bacterial phenotypes, complementing the bactericidal ability of traditional antibiotics. In this work, several novel acetylene analogues of fimbrolides were synthesised in moderate to high yields via Sonogashira coupling reactions of brominated furanones 4-bromo-5-(bromomethylene)furan-2(5H)-one 4 and 5-(dibromomethylene)-3-ethylfuran-2(5H)-one 5. The Sonogashira reaction of acetylenes on 4-bromo-5-(bromomethylene)furan-2(5H)-one 4 was favoured at the C5 methylene bromide over the C4 bromide substituent. On biological testing, the most potent compounds 13 and 14 showed 82 and 98 % bacterial quorum-sensing inhibitory (QSI) activity against Pseudomonas aeruginosa reporter strain respectively.