Alkynes Research Articles

Carbon-carbon triple bond cleavage and reconstitution to achieve aryl amidation using nitrous acid esters

C–C bond cleavage and recombination provide an efficient strategy for the modification and reconstruction of molecule structures. Herein, we present a method for achieving amidation of aryl C(sp2)–H bond through the cleavage and recombination of C–C triple bond with the involvement of nitrous acid esters. This method marks the instance of precise and controlled stepwise cleavage of C–C triple bond, offering a fresh perspective for the cleavage of such bonds. Nitrous acid ester serves as both a radical source and a hydrogen atom transfer (HAT) reagent to functionalize and utilize the two carbon atoms of the C–C triple bond. The alkoxy radical captures the hydrogen atom from the aryl C(sp2)–H bond or N-hydroxyl to induce the 1,3-oxygen radical migration, which is crucial for the subsequent cleavage of the C–C bond.

Identifying Carbon-Carbon Triple Bonds from Double Bonds via Single-Molecule Conductance.

Molecular-scale electronics focuses on understanding and utilizing charge transport through individual molecules. A key issue is the charge transport capability of a single molecule characterized by current decay. We visualize the on-site formation of conjugated polymers with varying carbon-carbon bond orders by using scanning tunneling microscopy and noncontact atomic force microscopy. Although carbon-carbon double bonds and triple bonds exhibit similar electronic characteristics, single-molecule conductance measurements reveal distinct features based on different levels of conjugation. These findings, supported by density functional theory calculations, indicate that a higher bond order results in greater electron density and more symmetric molecular orbitals, leading to larger transmission rates and more rigid frontier orbitals. Consequently, this contributes to a higher conductance and a lower decay constant. These findings enhance the understanding of bond orders in molecular electronics and should facilitate the development of single-molecule devices and the applications of nanoscale circuitry.

UNUSUAL TRANSFORMATIONS OF 2,3- AND 1,3- BUTHANEDIOL MONOPROPARGYL ETHERS

Research in the field of chemistry of oxygen-containing derivatives of acetylene has acquired considerable interest. Of the simple ethers containing a triple carbon-carbon bond, ethynyl and propargyl ethers of monohydric alcohols and phenols, as well as alkyl and aryl ethers of acetylene glycols have been studied in most detail. Alkynyl, especially propargyl mono- and diesters of polyhydric alcohols have not been studied extensively. Due to the presence of highly reactive centers, ethers occupy a special place in the field of chemistry of oxygen-containing derivatives of acetylenes. Acetylene ethers of glycols usually form ketoxy esters under conditions of acid-catalytic hydration. Using the tendency of propargyl compounds to prototropy in a basic medium, we studied under these conditions the possibility of converting monopropargyl ethers of 2,3- and 1,3-butanediols into oxygen-containing heterocycles. The available data indicate that these types of triple-bonded ethers are of great interest, both theoretically and practically. Among acetylenic ethers of polyhydric alcohols, which are the most interesting class of oxygen-containing alkynes in terms of synthesis and practice, propargyl ethers of acyclic glycols have been studied. In this regard, we have undertaken an experimental study of the synthesis routes of mono- and dipropargyl ethers of glycols and their unusual transformations. Acetylene ethers have proven themselves to be very valuable substances used in various fields of organic synthesis and exhibiting interesting properties of applied nature. Propargyl mono- and diesters of polyhydric alcohols with a triple bond are of great interest, both theoretically and practically. The paper presents the results of a study of acid-catalytic intramolecular cyclohydration and the synthesis of heterocyclic compounds based on propargyl ethers of glycols. The latter were monopropargyl ethers of 2,3- and 1,3-butanediols (I, II). The structure of the obtained heterocyclic compounds was confirmed by NMR and IR absorption spectra. Keywords: cyclohydration, monopropargyl ethers, heterocyclization, butanediols, spectrum, dioxane, t-BuO, NaOH.

Novel Methods for the Formation of Free Carbyne Radicals in Solution.

Carbyne free radicals (RC) are usually associated with high-energy processes, thus research on their preparation, chemical reactivity, and prevalence under mild conditions is scarce. Recently, it was reported that metallo-complexes containing CR ligands may undergo spontaneous degradation in aqueous solutions to produce free RC radicals. These highly reactive species may react with each other to form the corresponding alkyne and other products. The reaction of 1,1,1 halo-carbo-hydrates with Cr(II) ions also forms RC radicals under mild conditions. Herein, we report two additional synthetic routes that produce free RC radicals under mild conditions. First, the reaction between metallic zinc and acetic anhydride produces 2-butyne and several other C2, C3, and C4 compounds. Isotopic-labeling experiments indicate that the formation of 2-butyne results from an inter-molecular reaction in which two RC moieties from two acetic anhydride molecules combine in solution. In addition, the degradation of the tri-molybdenum complex [Mo3(H3CC≡CCH3)(OAc)(H2O)2Br7], in which a 2-butyne ligand is coordinated to the Mo3 framework in a μ3-η2 (⊥) binding mode in aqueous solution produces several C2, C3, C4 and C5 molecules. This indicates the formation of free CH3C radicals by a homolytic cleavage of the carbon-carbon triple bond.

Reshaping the aggregation landscape of benzothiadiazole employing steroidal scaffolds and conformationally free alkyne tethers

In this study, we target the introduction of conformational freedom to BTD, aiming to unlock new solid-state arrangements that were previously inaccessible, while striving to maintain its high fluorescence quantum yield. Our approach is grounded in a detailed exploration of the conformational space of designed molecules, employing molecular mechanics to predict and evaluate the impact of structural modifications on solubility and solid-state behavior. By strategically flanking the BTD core with steroidal fragments through alkyne bridges, we not only introduce bulky elements that disrupt the native crystal-packing landscape of pristine BTD, but also ensure significant rotational freedom around the carbon-carbon triple bonds. This design strategy allows the molecules to explore a wide range of conformations, potentially facilitating the formation of novel solid-state supramolecular arrangements.The synthesis of these compounds revealed that they exhibit adequate processability in solution and form solids that prove crystalline by powder X-ray diffraction, but do not readily form macroscopic crystals as BTD normally does. The steroid fragments play a crucial role in determining the supramolecular organization of these compounds. Depending on the specific functional groups present on the steroid skeleton, primary interactions such as hydrogen bonding and secondary interactions related to facial amphiphilicity dictate the overall arrangement of molecules in the solid state.Remarkably, the modifications successfully preserve the intrinsic high fluorescence quantum yield of the BTD core. This achievement underscores the potential of incorporating conformational flexibility into molecular design to access new material properties while retaining desirable photophysical characteristics.

Catalytic engineering of transition metal (TM: Ni, Pd, Pt)-coordinated Ge-doped graphitic carbon nitride (Ge@g-c3n4) nanostructures for petroleum hydrocarbon separation: An outlook from theoretical calculations

The extraction, processing, and utilization of petroleum often results in the release of diverse hydrocarbon pollutants into the environment, leading to severe ecological and health implications. Herein, the adsorption and separation of ethane (EAN), ethene (EEN), ethyne (EYN), and benzene (BZN) fractions of paraffin, olefin, acetylene, and aromatic petroleum hydrocarbons were investigated via the catalytically engineered nickel group transition metals; nickel (Ni), palladium (Pd), and platinum (Pt). These transition metals were coordinated on Germanium-doped graphitic carbon nitride (Ge@g-C3N4) nanostructures, and the behavior of the systems was studied through Kohn–Sham density functional theory (KS-DFT) with the B3LYP–D3(BJ)/Def2-SVP computational method. The adsorption of petroleum hydrocarbons decreased in the order Ge_Ni@C3N4 > Ge_Pd@C3N4 > Ge_Pt@C3N4>Ge_Pt@C3N4. These results showed that the coordination of Ni, Pd, and Pt within Ge@C3N4 improved the separation of petroleum hydrocarbons.

Syntheses of Phosphonylated Pyrido-Dihydrofurans by Regioselective 5-Exo-dig Addition to Carbon-Carbon Triple Bond Catalyzed by AgNO3.

The tandem nucleophilic addition-cyclization reaction of o-alkynylpyridinecarbaldehyde 1 with dialkyl phosphites 2 took place very smoothly in the presence of AgNO3 under base conditions in DCE at 50 °C. In all cases, the reaction proceeded in a regioselective manner leading to the 5-exo-dig phosphonylated pyrido-dihydrofurans 3 in moderate to good yields.

Facile synthesis of diphosphoryl acetylenes through copper-catalyzed cross coupling

Organic molecules containing 1,2-diphosphonate moiety are of great value in organic synthesis. Diphosphoryl acetylenes (or named as ethyne-1,2-diyldiphosphonates) are a class of molecules utilized for synthesis of diverse phosphorus compounds applicable in multiple fields. However, present stoichiometric methods for the preparation of diphosphoryl acetylenes generally requires multiple steps or harsh conditions. Herein, we report a facile synthesis of diphosphoryl acetylenes, in which the readily available ethynyl phosphonates couple with dialkyl phosphonates through cheap copper catalysis. A series of diphosphoryl acetylenes in symmetric or unsymmetric fashions are facilely prepared. This protocol demonstrates advantages of mild reaction conditions, inert atmosphere-free, cheap catalyst, base-free, and high efficiency to serve as a practical method for synthesis of diphosphoryl acetylenes.

Axial Ligand Enables Synthesis of Allenylsilane through Dirhodium(II) Catalysis.

Described herein is a dirhodium(II)-catalyzed silylation of propargyl esters with hydrosilanes, using tertiary amines as axial ligands. By adopting this strategy, a range of versatile and useful allenylsilanes can be achieved with good yields. This reaction not only represents a SN2'-type silylation of the propargyl derivatives bearing a terminal alkyne moiety to synthesize allenylsilanes from simple hydrosilanes, but also represents a new application of dirhodium(II) complexes in catalytic transformation of carbon-carbon triple bond. The highly functionalized allenylsilanes that are produced can be transformed into a series of synthetically useful organic molecules. In this reaction, an intriguing ON-OFF effect of the amine ligand was observed. The reaction almost did not occur (OFF) without addition of Lewis base amine ligand. However, the reaction took place smoothly (ON) after addition of only catalytic amount of amine ligand. Detailed mechanistic studies and density functional theory (DFT) calculations indicate that the reactivity can be delicately improved by the use of tertiary amine. The fine-tuning effect of the tertiary amine is crucial in the formation of the Rh-Si species via a concerted metalation deprotonation (CMD) mechanism and facilitating β-oxygen elimination.

Nickel-catalyzed defluorinative asymmetric cyclization of Trifluoromethyl-substituted 1,6-Enynes: Insights from DFT calculations on the reaction mechanism and selectivity

Density functional theory (DFT) calculations were employed to elucidate the mechanism and selectivity of nickel-catalyzed defluorinative asymmetric cyclization reactions of trifluoromethyl-substituted 1,6-enynes. The results indicate that the product is formed via a stepwise addition cyclization mechanism, including sequential steps of ligand coordination, transmetalation, ligand exchange, alkyne insertion, olefin insertion, β-F elimination, another transmetalation, and a final ligand exchange. The regioselectivity is primarily governed by the alkyne insertion step, where electrostatic interactions strongly favor 1,2-insertion of the carbon-carbon triple bond over 2,1-insertion. The enantioselectivity is largely determined during the insertion step of the olefin insertion step, with the (S)-product forming preferentially over the (R)-product due to stronger non-covalent interactions between the ligand and the substrate, minimal catalyst conformational distortion, and enhanced electronic interactions between the catalyst and the substrate.

Remote Functionalization by Pd-Catalyzed Isomerization of Alkynyl Alcohols.

In recent years, progress has been made in the development of catalytic methods that allow remote functionalizations based on alkene isomerization. In contrast, protocols based on alkyne isomerization are comparatively rare. Herein, we report a general Pd-catalyzed long-range isomerization of alkynyl alcohols. Starting from aryl-, heteroaryl-, or alkyl-substituted precursors, the optimized system provides access preferentially to the thermodynamically more stable α,β-unsaturated aldehydes and is compatible with potentially sensitive functional groups. We showed that the migration of both π-components of the carbon-carbon triple bond can be sustained over several methylene units. Computational investigations served to shed light on the key elementary steps responsible for the reactivity and selectivity. These include an unorthodox phosphine-assisted deprotonation rather than a more conventional β-hydride elimination in the final tautomerization event.

Encapsulation and Evolution of Polyynes Inside Single-Walled Carbon Nanotubes.

Polyyne is an sp-hybridized linear carbon chain (LCC) with alternating single and triple carbon-carbon bonds. Polyyne is very reactive; thus, its structure can be easily damaged through a cross-linking reaction between the molecules. The longer the polyyne is, the more unstable it becomes. Therefore, it is difficult to directly synthesize long polyynes in a solvent. The encapsulation of polyynes inside carbon nanotubes not only stabilizes the molecules to avoid cross-linking reactions, but also allows a restriction reaction to occur solely at the ends of the polyynes, resulting in long LCCs. Here, by controlling the diameter of single-walled carbon nanotubes (SWCNTs), polyynes were filled with high yield below room temperature. Subsequent annealing of the filled samples promoted the reaction between the polyynes, leading to the formation of long LCCs. More importantly, single chiral (6,5) SWCNTs with high purity were used for the successful encapsulation of polyynes for the first time, and LCCs were synthesized by coalescing the polyynes in the (6,5) SWCNTs. This method holds promise for further exploration of the synthesis of property-tailored LCCs through encapsulation inside different chiral SWCNTs.

Spontaneous dispersion of metallic nickel centers in inert metal substrate for the selective hydrogenation of carbon-carbon triple bonds

Spontaneous dispersion of metallic nickel centers in inert metal substrate for the selective hydrogenation of carbon-carbon triple bonds

Ru(II)-Catalyzed Deoxygenative Formal [3 + 1 + 2] Benzannulation of Allyl Alcohols and Acetylenediesters via C-H Activation and Selective Carbon-Carbon Triple Bond Cleavage.

An unprecedented Ru(II)-catalyzed deoxygenative, site-selective formal [3 + 1 + 2] benzannulation reaction for the efficient synthesis of highly substituted benzene molecules is reported. This reaction between allyl alcohols and acetylenedicarboxylate esters proceeds via cascade C-H activation, consecutive double migratory insertion with alkynes, and cycloaromatization followed by an unusual specific C-C triple bond cleavage.

Copper-Catalyzed Regio- and Stereoselective Hydroarylation of Ynamide.

Presented herein is a copper-catalyzed trans-hydroarylation of ynamides. The reaction showcases the assembly of boronic acids across the carbon-carbon triple bond of ynamides. The reaction proceeds under mild conditions offering a complementary approach for the versatile synthesis of multifunctional (E)-α,β-disubstituted enamides. Moreover, the hydroarylation process is highly regio- and stereoselective. The transformation shows a broad scope (30 examples) and tolerates a wide range of labile functional groups. Control experiments provide substantive evidence supporting the mechanistic cycle and the observed selectivity.

Peroxodisulfate-assisted synthesis of 2-thiocyanato glycals and their transformation to C-2-thio acrylo/aryl nitrile-substituted glycals.

An efficient regioselective method to attach thiocyanato groups at the β-position of enol double bonds in sugar enol ethers using KSCN and potassium persulfate has been developed. The highly regioselective addition of the resulting sugar thiocyanate to electron rich species like terminal alkynes and benzynes under Pd catalysis generated C-2-thio acrylo/aryl nitrile glycals via simultaneous introduction of thio and cyano groups into carbon-carbon triple bonds.

Ni-catalysed assembly of axially chiral alkenes from alkynyl tetracoordinate borons via 1,3-metallate shift.

Asymmetric synthesis based on a metallate shift of tetracoordinate borons is an intriguing and challenging topic. Despite the construction of central chirality from tetracoordinate boron species via a 1,2-metallate shift, catalytic asymmetric synthesis of axially chiral compounds from such boron 'ate' complexes is an ongoing challenge. Axially chiral alkenes have received great attention due to their unique characteristics and intriguing molecular scaffolds. Here we report an enantioselective nickel-catalysed strategy for the construction of axially chiral alkenes via a 1,3-metallate shift of alkynyl tetracoordinate boron species. The chemoselectivity, regioselectivity and atroposelectivity can be regulated and well-controlled from readily accessible starting materials with a cheap transition-metal catalyst. Downstream transformations indicate the powerful conversion ability of such compounds in this protocol, and late-stage elaborations of bioactive compounds can also be achieved. Mechanistic experiments reveal that regioselective syn-addition of an aryl-Ni complex with a carbon-carbon triple bond and subsequent 1,3-phenyl migration are the two key steps for the synthesis of axially chiral alkenes.

Bacterial polyynes uncovered: a journey through their bioactive properties, biosynthetic mechanisms, and sustainable production strategies.

Covering: up to 2023Conjugated polyynes are natural compounds characterized by alternating single and triple carbon-carbon bonds, endowing them with distinct physicochemical traits and a range of biological activities. While traditionally sourced mainly from plants, recent investigations have revealed many compounds originating from bacterial strains. This review synthesizes current research on bacterial-derived conjugated polyynes, delving into their biosynthetic routes, underscoring the variety in their molecular structures, and examining their potential applications in biotechnology. Additionally, we outline future directions for metabolic and protein engineering to establish more robust and stable platforms for their production.

Gem-Difluorination of carbon-carbon triple bonds using Brønsted acid/Bu4NBF4 or electrogenerated acid.

gem-Difluorination of carbon-carbon triple bonds was conducted using Brønsted acids, such as Tf2NH and TfOH, combined with Bu4NBF4 as the fluorine source. The electrochemical oxidation of a Bu4NBF4/CH2Cl2 solution containing alkyne substrates could also give the corresponding gem-difluorinated compounds (in-cell method). The ex-cell electrolysis method was also applicable for gem-difluorination of alkynes.

Photoredox-Catalyzed Divergent Radical Cascade Annulations of 1,6-Enynes via Pyridine N-Oxide-Promoted Vinyl Radical Generation.

The divergent organophotoredox-catalyzed radical cascade annulation reactions of 1,6-enynes were developed. A series of cyclopropane-fused hetero- and carbo-bicyclic, tricyclic, and spiro-tetracyclic compounds were facilely synthesized from a broad scope of 1,6-enynes and 2,6-lutidine N-oxide under mild and metal-free conditions with blue light-emitting diode light irradiation. The cascade annulation reaction occurs with the intermediacy of a β-oxyvinyl radical, which is produced from photocatalytically generated pyridine N-oxy radical addition to the carbon-carbon triple bond.