Aliphatic Alkynes Research Articles

ChemInform Abstract: Copper Nanoparticle Catalyzed Formation of C—S Bonds Through Activation of S—S and C—H Bonds: An Easy Route to Alkynyl Sulfides.

AbstractThe scalable reaction of diphenyl sulfide with aliphatic terminal alkynes is not applicable the corresponding transformation of 1‐ethynylcyclohexene.

Improved molecular weight control in ring‐opening metathesis polymerization reactions in organic and aqueous media using N‐heterocyclic carbene–ruthenium arene/alkyne catalyst systems

A binary catalytic system, RuCl2(N‐heterocyclic carbene)(p‐cymene)/alkyne, was developed for improved molecular weight control in ring‐opening metathesis polymerization (ROMP) reactions of norbornene derivatives in organic and aqueous media. Monometallic ruthenium arene compounds were activated using aryl and aliphatic terminal alkynes to form highly active metathesis species. The effects of alkyne structure and concentration on the overall catalytic activity were systematically investigated. The catalytic activity of the metathesis active species can be tuned by varying alkyne substituents. Also, the initiation rate of the ROMP reaction can be tuned by increasing the alkyne‐to‐Ru ratio. ROMP polymers with a wide range of molecular weights (91–832 kDa) were isolated in organic media, whereas polymers with a molecular weight range of 110–280 kDa with average particle sizes of 150–250 nm were isolated in aqueous media. Copyright © 2016 John Wiley & Sons, Ltd.

ChemInform Abstract: Cobalt‐Catalyzed Cyclization of Aliphatic Amides and Terminal Alkynes with Silver‐Cocatalyst.

AbstractThe reaction is successfully extended to aromatic amides to yield various isoindolinones.

ChemInform Abstract: Copper‐Catalyzed Direct Transformation of Simple Alkynes to Alkenyl Nitriles via Aerobic Oxidative N‐Incorporation.

AbstractA novel direct transformation of aliphatic terminal alkynes to alkenyl nitriles through the incorporation of a nitrogen atom into the simple hydrocarbons is reported.

Kinetic study of thermal polymerization reactions between diazide and different diynes

The reaction kinetics between diazide(4,4’-biphenyl dibenzyl azide) and different diynes (dipropargyl bisphenol A and 1,3-diethynylbenzene) were studied by means of differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (1H-NMR). DSC was adopted to analyze the reactions under bulk polymerization condition, while 1H-NMR for solution reaction polymerization was conducted. The apparent activation energies (Eα) calculated by Kissinger’s method were 77.96, 81.24 kJ/mol, which were confirmed by Friedman’s method, and 65.45, 69.36 kJ/mol by 1H-NMR for dispropargyl bisphenol A/4,4’-biphenyl dibenzyl azide and 1,3-diethynylbenzene/4,4’-biphenyl dibenzyl azide, respectively. The polymerizations between the diazide and diynes were first-order reactions based on calculation from both DSC and 1H-NMR. The results showed that the reaction between dipropargyl bisphenol A and 4,4’-biphenyl dibenzyl azide was easier than that between 1,3-diethynylbenzene and 4,4’-biphenyl dibenzyl azide, verifying that the reactivity of aliphatic alkyne was higher than that of aromatic alkyne.

C−C Bond‐Forming Strategy by Manganese‐Catalyzed Oxidative Ring‐Opening Cyanation and Ethynylation of Cyclobutanol Derivatives

AbstractA novel C−C bond‐forming strategy employing manganese‐catalyzed ring‐opening of cyclobutanol substrates, followed by cyanation or ethynylation, is described. A cyano C1 unit and ethynyl C2 unit are regiospecifically introduced to the γ‐position of ketones at room temperature, providing a mild yet powerful method for production of elusive aliphatic nitriles and alkynes. All transformations described are based on a common sequence: 1) oxidative ring‐opening of cyclobutanol substrates by C−C bond cleavage; 2) radical addition to triple bonds bearing an arylsulfonyl group; and 3) radical‐mediated C−S bond cleavage.

C-C Bond-Forming Strategy by Manganese-Catalyzed Oxidative Ring-Opening Cyanation and Ethynylation of Cyclobutanol Derivatives.

A novel C-C bond-forming strategy employing manganese-catalyzed ring-opening of cyclobutanol substrates, followed by cyanation or ethynylation, is described. A cyano C1 unit and ethynyl C2 unit are regiospecifically introduced to the γ-position of ketones at room temperature, providing a mild yet powerful method for production of elusive aliphatic nitriles and alkynes. All transformations described are based on a common sequence: 1) oxidative ring-opening of cyclobutanol substrates by C-C bond cleavage; 2) radical addition to triple bonds bearing an arylsulfonyl group; and 3) radical-mediated C-S bond cleavage.

Urea as mild and efficient additive for palladium catalyzed Sonogashira cross coupling reaction

A catalytic system based on Pd(OAc)2/urea has been developed for Sonogashira cross coupling of aryl halides with terminal alkynes at room temperature. This catalytic system effectively promotes Sonogashira coupling of both aryl iodides and aryl bromides to give polyfunctional alkynes under copper and amine free conditions. The catalytic system is readily accessible, inexpensive and highly flexible for both aromatic and aliphatic alkynes.

ChemInform Abstract: Convenient Synthesis of 2‐Alkynylbenzazoles Through Sonogashira Cross‐Coupling Reaction Between Thioethers and Terminal Alkynes.

AbstractThe coupling reaction proceeds under aerobic conditions with aromatic and aliphatic alkynes to give 2‐alkynyl substituted benzoxazoles and benzothiazoles.

Ammonium Chloride/B(C6F5)3System Catalyzed Selective Addition of Acids to Alkynes

Development of straightforward and selective approaches to functionalize vinyl groups is an important and continuing goal. A novel convenient route to vinylhalides or enol esters by a Markovnikov regioselective addition of hydrogen chloride or carboxylic acid to the C≡C bond of alkynes in the presence of an ammonium hydrochloride/B(C6F5)3 catalytic system is reported. Thus, when treated with catalytic amounts of ammonium hydroborate ([TMPH]+[Cl-B(C6F5)3] ), equimolar mixtures of hydrogen chloride and alkynes are converted into a variety of chloroalkenes as monoadducts. The yields of the monoadducts are usually higher than 90% for terminal aromatic alkynes, while for the terminal aliphatic alkynes they are considerably lower, with the worst observed for sterically hindered tert-butylacetylene (only 67%). NMR monitoring of the reaction mixtures reveals that under ambient conditions the main by-products are the corresponding diadducts (gem-dihalides). At higher temperatures (50 °C) for equimolar alkyne/HCl mixtures or at ambient temperature for alkyneenriched mixtures, the diadduct formation can be nearly completely suppressed. Noteworthy, that both ammonium and borane (-ate) components of the catalytic system are essential for the conversion success. In the case of trifuoroacetic acid addition to alkynes, presence of the ammonium component is not required, with the reaction yields usually exceeding 95% for terminal aromatic alkynes and being modest to good for the aliphatic ones. The reported catalytic system presents the first example of the “metal-free” catalysts for the selective addition of acids to alkynes.

Metal free carboamination of internal alkynes--an easy access to polysubstituted quinolines.

A metal free carboamination of unactivated alkynes towards highly substituted quinolines was realized in the presence of a synergistic Brønsted acid catalyst system. Supported by mechanistic probes, the reaction proceeds via a highly reactive vinyl cation in a C-C bond formation--Schmidt reaction sequence. The irreversible extrusion of N2, as a powerful driving force, allows for a general conversion of poorly nucleophilic aliphatic alkynes.

Rh-Catalyzed Intermolecular Reactions of α-Alkyl-α-Diazo Carbonyl Compounds with Selectivity over β-Hydride Migration.

Rh-carbenes derived from α-diazocarbonyl compounds have found broad utility across a remarkable range of reactivity, including cyclopropanation, cyclopropenation, C-H insertions, heteroatom-hydrogen insertions, and ylide forming reactions. However, in contrast to α-aryl or α-vinyl-α-diazocarbonyl compounds, the utility of α-alkyl-α-diazocarbonyl compounds had been moderated by the propensity of such compounds to undergo intramolecular β-hydride migration to give alkene products. Especially challenging had been intermolecular reactions involving α-alkyl-α-diazocarbonyl compounds. This Account discusses the historical context and prior limitations of Rh-catalyzed reactions involving α-alkyl-α-diazocarbonyl compounds. Early studies demonstrated that ligand and temperature effects could influence chemoselectivity over β-hydride migration. However, effects were modest and conflicting conclusions had been drawn about the influence of sterically demanding ligands on β-hydride migration. More recent advances have led to a more detailed understanding of the reaction conditions that can promote intermolecular reactivity in preference to β-hydride migration. In particular, the use of bulky carboxylate ligands and low reaction temperatures have been key to enabling intermolecular cyclopropenation, cyclopropanation, carbonyl ylide formation/dipolar cycloaddition, indole C-H functionalization, and intramolecular bicyclobutanation with high chemoselectivity over β-hydride migration. Cyclic α-diazocarbonyl compounds have been shown to be particularly resilient toward β-hydride migration and are the first class of compounds that can engage in intermolecular reactivity in the presence of tertiary β-hydrogens. DFT calculations were used to propose that for cyclic α-diazocarbonyl compounds, ring constraints relieve steric interaction for intermolecular reactions and thereby accelerate the rate of intermolecular reactivity relative to intramolecular β-hydride migration. Enantioselective reactions of α-alkyl-α-diazocarbonyl compounds have been developed using bimetallic N-imido-tert-leucinate-derived complexes. The most effective complexes were found by computation and X-ray crystallography to adopt a "chiral crown" conformation in which all of the imido groups are presented on one face of the paddlewheel complex in a chiral arrangement. Insight from computational studies guided the design and synthesis of a mixed ligand paddlewheel complex, Rh2(S-PTTL)3TPA, the structure of which bears similarity to the chiral crown complex Rh2(S-PTTL)4. Rh2(S-PTTL)3TPA engages substrate classes (aliphatic alkynes, silylacetylenes, α-olefins) that are especially challenging in intermolecular reactions of α-alkyl-α-diazoesters and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh2(S-PTTL)4. The work detailed in this Account describes progress toward enabling a more general utility for α-alkyl-α-diazo compounds in Rh-catalyzed carbene reactions. Further studies on ligand design and synthesis will continue to broaden the scope of their selective reactions.

Bifunctional Ligand-Assisted Catalytic Ketone α-Alkenylation with Internal Alkynes: Controlled Synthesis of Enones and Mechanistic Studies.

Here, we describe a detailed study of the rhodium(I)-catalyzed, bifunctional ligand-assisted ketone α-C-H alkenylation using internal alkynes. Through controlling the reaction conditions, conjugated enamines, α,β- or β,γ-unsaturated ketones, can be selectively accessed. Both aromatic and aliphatic alkynes can be employed as coupling partners. The reaction conditions also tolerate a broad range of functional groups, including carboxylic esters, malonates, secondary amides, thioethers, and free alcohols. In addition, excellent E-selectivity was observed for the tetra-substituted alkene when forming the α,β-unsaturated ketone products. The mechanism of this transformation was explored through control experiments, kinetic monitoring, synthesizing the rhodium-hydride intermediates and their reactions with alkynes, deuterium-labeling experiments, and identification of the resting states of the catalyst.

ChemInform Abstract: Combining Pd(π‐Allyl)Cp and PPh3 as a Unique Catalyst for Efficient Synthesis of Alkyliodo Indoles via C(sp3)—I Reductive Elimination.

The combination of Pd(π-allyl)Cp and PPh3 was found to generate an efficient catalyst for the formation of indole-containing alkyl iodides from ortho-amino iodobenzenes and both aromatic and aliphatic alkynes. A unique feature of this reaction is a palladium-promoted C(sp3)–I bond formation via reductive elimination. This catalytic process was found to be very sensitive to the size and equivalents of phosphine ligands and the nature of the base.

ChemInform Abstract: Direct Synthesis of β‐Ketophosphonates and Vinyl Phosphonates from Alkenes or Alkynes Catalyzed by CuNPs/ZnO.

AbstractIt is found that alkynes conjugated with an aromatic ring or a carbon‐carbon double bond afford β‐ketophosponates as main products, whereas aliphatic alkynes or alkynes conjugated with a carbonyl group afford the corresponding vinyl phosphonates as mixtures of E/Z‐isomers.

Cross‐Dehydrogenative Coupling of Tertiary Amines and Terminal Alkynes Catalyzed by Copper Nanoparticles on Zeolite

AbstractA wide range of catalysts based on supported copper nanoparticles have been prepared and tested in the cross‐dehydrogenative coupling of tertiary amines and terminal alkynes. Copper nanoparticles on zeolite Y were found to be the most effective catalyst in the presence of tert‐butyl hydroperoxide as the oxidant. Contrary to the previously reported methodologies involving copper catalysts, reactions have been accomplished without the need of an inert atmosphere and in the absence of solvent, using 1.5 mol% catalyst. A variety of tertiary amines, including aromatic, benzylic and aliphatic ones, have been coupled with both aromatic and aliphatic alkynes to furnish the corresponding propargylamines in moderate‐to‐excellent yields. The procedure has been successfully scaled‐up to 12 mmol with a high conversion (93%). Moreover, the catalyst has been reused in seven cycles maintaining a good performance. Its catalytic activity has been compared with that of an array of commercial copper catalysts, being superior as regards the conversion and minimizing the alkyne homocoupling as a side reaction. The negative filtration test points to a heterogeneous nature of the process. Based on compelling experimental evidence, a novel reaction mechanism has been delineated which outlines the essential role of free radicals and the couple copper(I)/copper(II).magnified image

ChemInform Abstract: Unimolecular Tetrakis‐piperidine‐4‐ol: An Efficient Ligand for Copper and Amine Free Sonogashira Coupling.

A unimolecular tetrakis-piperidine-4-ol has been developed as an efficient ligand in combination with Pd/C for copper and amine free Sonogashira coupling. Various aryl and heteroaryl iodides were successfully coupled with aliphatic and aromatic alkynes to give internal alkynes in good to excellent yields.

Cobalt-Catalyzed Cyclization of Aliphatic Amides and Terminal Alkynes with Silver-Cocatalyst.

A new method of cobalt-catalyzed synthesis of pyrrolidinones from aliphatic amides and terminal alkynes was discovered through a C-H bond functionalization process on unactivated sp(3) carbons with the silver cocatalyst using a bidentate auxiliary. For the first time, a broad range of easily accessible alkynes are exploited as the reaction partner in C(sp(3))-H bond activation to give the important 5-ethylidene-pyrrolidin-2-ones in a site-selective fashion. The reaction tolerates a wide variety of functional groups including -F, -Cl, -Br, -CF3, ether, cyclopropane, and thiophene. Both pyridine ligand and aromatic solvent play the important role for the promotion of reactivity. This cobalt-catalyzed cyclization reaction can be successfully extended to a variety of aromatic amides to afford a variety of isoindolinones. Attractive features of this catalytic system include its low cost, easy operation, and convenient access to a wide range of pyrrolidinones and isoindolinones.

Silver-containing microemulsion as a high-efficient and recyclable catalytic system for hydration of alkynes

A silver-catalyzed highly efficient and regioselective synthesis of ketones from a wide range of alkynes is described. The reaction is dramatically accelerated by its performance in aqueous emulsion, which is self-assembled by the addition of silver perfluorooctanesulfonate (1) and perfluorooctanesulfonic acid (PFOS) to water. The reaction is conducted under convenient conditions with broad substrate scope, including a variety of aromatic and aliphatic terminal alkynes and internal alkynes. Furthermore, the air- and light-stable silver catalytic microemulsion can be reused for 4 times with minimal change in catalytic efficiency.

Ligand- and Acid-Free Gold(I) Chloride Catalyzed Hydration of Terminal Alkynes

Our work shows that simple alkynes can be hydrated by the AuCl/MeOH catalyst system to afford the corresponding methyl ketones in moderate to high yields without any additive, ligand, or acid promoter. This methodology is simpler, milder, and operationally easier than those reported before. The reaction media significantly affects the reaction, and methanol is found to be the best solvent. Both aliphatic and aromatic terminal alkynes were able to undergo hydration, affording moderate to excellent yields under the reaction conditions used in the present work, and excellent functional-group tolerance was also observed. A plausible mechanism for the hydration reaction was proposed.