Activation Of Alkynes Research Articles

Selective propargylic C(sp3)-H activation of methyl-substituted alkynes versus [2 + 2] cycloaddition at a titanium imido template.

The reaction of the titanium imido complex 1b with 2-butyne leads to the formation of the titanium azadiene complex 2a at ambient temperature instead of yielding the archetypical [2 + 2] cycloaddition product (titanaazacyclobutene) which is usually obtained by combining titanium imido complexes and internal alkynes. The formation of 2a is presumably caused by an initial propargylic C(sp3)–H activation step and quantum chemical calculations suggest that the outcome of this unexpected reactivity is thermodynamically favored. The previously reported titanaazacyclobutene I (which is obtained by reacting 1b with 1-phenyl-1-propyne) undergoes a rearrangement reaction at elevated temperature to give the corresponding five-membered titanium azadiene complex 2b.

Metal-free multicomponent approach for the synthesis of propargylamine: a review.

Propargylamines are important classes of alkyne coupled amine compounds used in heterocyclic chemistry and pharmaceuticals chemistry and have a large impact as a pharmacophore used in medicinal chemistry. One of the straightforward approaches for the synthesis of this class of compound is A3 coupling, a three-component coupling reaction among aldehyde, alkyne (terminal acetylene) and amine. However, there are many methods other than conventional three component alkyne–aldehyde–amine (A3) coupling which have also been reported for the synthesis of propargylamine. Most of these methods are based on the metal catalyzed activation of terminal alkyne. From the perspective of green and sustainable chemistry, the scientific community should necessarily focus on metal-free techniques which can access a variety of propargylamines. There are only a few reports found in the literature where propargylamines were successfully synthesized under metal-free conditions. This present review article neatly and precisely encompasses the comprehensive study of metal-free protocols in propargylamine synthesis putting forth their mechanisms and other aspects.

Cu(II)-Containing Nano-Silica Triazine Based Dendrimer: A Green and Proficient Catalyst for the Synthesis of Propargylamines

One-pot multicomponent reactions are an attractive synthetic strategy to generate multiple molecular scaffolds. Activation of a terminal alkyne C–H bond by transition metal catalysts is a reaction of fundamental interest in organic synthesis. One of the best examples of such a process is three components coupling of aldehydes, alkynes, and amines (A3-coupling). Herein, Cu(II)-containing nano-silica triazine based dendrimer was prepared, characterized and utilized as a retrievable catalytic system (Cu(II)-TrDen@nSiO2) for green formation of propargylamines under solvent-free conditions. The various aldehydes/ketones, amines, and phenylacetylene were reacted at 100 °C in the presence of the 1.34 mol% of the catalyst to synthesize propargylamines in high yields (87%–98%). The prepared catalyst can be isolated assisted by a simple filtration and recovered for five courses without significant reduction in its efficiency. The as-prepared nano-catalyst was characterized by FT-IR, TEM, SEM, EDX, TGA and ICP. Performing the reactions in environmentally friendly and affordable conditions, the low catalyst percentage, high yield of products, short reaction times and easy workup are the merits of this protocol.

Development of a novel octahedron rhodium complex and its application to the alkynylation of isatin derivatives

A new octahedron rhodium complex was synthesized, which permits the direct activation of terminal alkynes and its reaction with isatin derivatives under an air atmosphere. An excellent yield (up to 99%) was obtained at a catalyst loading of 2 mol%.

Correction to "A Sequential Activation of Alkyne and C-H Bonds for the Tandem Cyclization and Annulation of Alkynols and Maleimides through Cooperative Sc(III) and Cp*-Free Co(II) Catalysis".

Correction to "A Sequential Activation of Alkyne and C-H Bonds for the Tandem Cyclization and Annulation of Alkynols and Maleimides through Cooperative Sc(III) and Cp*-Free Co(II) Catalysis".

Dynamic PdII /CuI Multimetallic Assemblies as Molecular Models to Study Metal-Metal Cooperation in Sonogashira Coupling.

Cooperation between two different metals plays a crucial role in many synergistic catalytic reactions, such as the Sonogashira C-C cross-coupling reaction, where an interaction between the Pd and Cu centers is proposed in the transmetalation step. Although several heterobimetallic Pd/Cu complexes were proposed as structural models of the active species in Sonogashira coupling, the detailed understanding of the metal-metal cooperation in transmetalation is still lacking in current systems. In this work, we report a stepwise and systematic approach to building heteromultimetallic Pd/Cu assemblies as a tool to study metal-metal cooperativity. We obtained fully characterized Pd/Cu multimetallic assemblies that show reactivity in alkyne activation, formation of catalytically relevant aryl/acetylide species, and C-C elimination, serving as functional models for Sonogashira reaction intermediates. The combined experimental and DFT studies highlight the importance of ligand-controlled coordination geometry, metal-metal distances and dynamics of the multimetallic assembly for transmetalation step.

Gold-catalyzed reaction of alkynes with diazonium salts under photoirradiation revisited: New alkoxyarylation variant leading to enol ethers

Since earlier work on the use of arenediazonium tetrafluoroborates under gold-photoredox co-catalyzed activation of alkynes has been developed using Ar3PAuCl salts, we focused on modifying the gold precatalyst. The use of the gold complex [Ph3PAuNTf2] allowed for a direct alkoxyarylation of alkynes to form enol ethers in a stereoselective manner, instead of the previously obtained ketones. The synthetic utility of these enol ethers was demonstrated with the controlled preparation of deuterated ketones and fluorinated ketals. Additionally, the mechanism of this alkoxyarylation variant has been explored with density functional theory (DFT) calculations.

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Summary Carboxylation of terminal alkynes with CO2 via direct C–H bond activation is a highly appealing way to capture and convert CO2 but faces great challenges and difficulty. Here, we report an efficient catalyst that is prepared simply through introduction of p-tert-butylaniline into graphite oxide powders followed by localized growth of Ag nanoparticles (NPs). The bulky nature of p-tert-butylaniline facilitates the powder exfoliation, giving rise to mass production of uniform modified graphene oxide (tert-GO) nanosheets of 4 nm in thickness. Notably, Ag/tert-GO shows excellent catalytic activity for converting alkynes regardless of containing electron-donating or electron-withdrawing groups under mild reaction conditions. The synergy of the amide linkages on tert-GO nanosheets and the supported small-sized Ag NPs is recognized as the vital role in promoting adsorption of CO2 and subsequent conversion.

A Sequential Activation of Alkyne and C-H Bonds for the Tandem Cyclization and Annulation of Alkynols and Maleimides through Cooperative Sc(III) and Cp*-Free Co(II) Catalysis.

[4 + 2] oxidative Diels-Alder reaction of readily available alkynols with maleimide is achieved for the rapid access of pthalimide-fused multicyclic compounds. The reaction is proposed to go through a sequence of Sc(OTf)3-catalyzed electrophilic cyclization, ligand exchange with Cp*-free cobalt, and C-H activation followed by maleimide insertion.

Tuning Activity and Selectivity during Alkyne Activation by Gold(I)/Platinum(0) Frustrated Lewis Pairs.

Introducing transition metals into frustrated Lewis pair systems has attracted considerable attention in recent years. Here we report a selection of three metal-only frustrated systems based on Au(I)/Pt(0) combinations and their reactivity toward alkynes. We have inspected the activation of acetylene and phenylacetylene. The gold(I) fragments are stabilized by three bulky phosphines bearing terphenyl groups. We have observed that subtle modifications on the substituents of these ligands proved critical in controlling the regioselectivity of acetylene activation and the product distribution resulting from C(sp)–H cleavage of phenylacetylene. A mechanistic picture based on experimental observations and computational analysis is provided. As a result of the cooperative action of the two metals of the frustrated pairs, several uncommon heterobimetallic structures have been characterized.

Small Gold(I) and Gold(I)-Silver(I) Clusters by C-Si Auration.

Auration of o‐trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho‐metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au6L4](X)2 are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag2O leads to gold–silver clusters [Au4Ag2L4](X)2. Oxo‐trigold(I) species [Au3O]+ were identified as the intermediates in the formation of the silver‐doped clusters. Other [Au5], [Au4Ag], and [Au12Ag4] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.

Fe(III)‐Catalyzed, Cyclizative Coupling between 2‐Alkynylbenzoates and Carbinols: Rapid Generation of Polycyclic Isocoumarins and Phthalides and Mechanistic Study

AbstractFeCl3 catalyzed, highly regioselective cyclizative coupling of internal alkynes with alcohols has been reported for the rapid synthesis of structurally divergent, complex isocoumarins and phthalides respectively in intermolecular and intramolecular fashion. This strategy exhibited very high substrate scope and efficiency and proceeds through the simultaneous formation of C−O and C−C bonds. Observations from a series of control experiments supported a) the mechanism as Lewis acid catalyzed dual activation of ester and alcohol, b) the role of carbocation for the enhanced rates of cyclization, i. e., activation of alkyne by carbocation, and c) no role of HCl in the reported cascade process.magnified image

Polyphenylene-Based Solid Acid as an Efficient Catalyst for Activation and Hydration of Alkynes.

Porous polymer catalysts possess the potential to combine the advantages of heterogeneous and homogeneous catalysis, namely, easy postreaction recycling and high dispersion of active sites. Here, we designed a −SO3H functionalized polyphenylene (PPhen) framework with purely sp2-hybridized carbons, which exhibited high activity in the hydration of alkynes including challenging aliphatic substrates such as 1-octyne. The superiority of the structure lies in its covalent crosslink in the xy-plane with a π–π stacking interaction between the planes, enabling simultaneously high swellability and porosity (653 m2·g–1). High acidic site density (2.12 mmol·g–1) was achieved under a mild sulfonation condition. Similar turnover frequencies (0.015 ± 0.001 min–1) were obtained regardless of acidic density and crosslink content, suggesting high accessibility for all active sites over PPhen. In addition, the substituted benzene groups can activate alkynes through a T-shape CH/π interaction, as indicated by the 8 and 16 cm–1 red shift of the alkyne C–H stretching peak for phenylacetylene and 1-octyne, respectively, in the infrared (IR) spectra. These advantages render PPhen-SO3H a promising candidate as a solid catalyst replacing the highly toxic liquid phase acids such as the mercury salt.

A novel fiber-supported cooperative catalyst for the carboxylation of terminal alkynes through CO2 utilization

Herein, a novel fiber-supported N-heterocyclic carbene (NHC) precursor and copper(I) composite (EIMBr-PANFTA@CuI), capable of acting as a cooperative catalyst for cleaner carboxylation of terminal alkynes from CO2, is presented. The EIMBr-PANFTA@CuI was synthesized systematically, and the resulting fiber samples from preparation and utilization processes were characterized detailedly. Moreover, the unique fiber-supported composite structure as a cooperative catalyst exhibited the synergistic effect on the activation of CO2 and terminal alkyne, which corporately contributed to the high catalytic performance on carboxylation for producing a series of alkyl 2-alkynoates in acetonitrile under ambient conditions. Furthermore, EIMBr-PANFTA@CuI was stable to air and moisture, and could be easily recovered with a tiny pair of tweezers and recycled with good activity over 10 runs. In addition, this protocol was convenient and effective for gram-scale experiments and thereby was prospective in practical applications.

Silver-mediated activation of terminal alkynes: A strategy to construct bis-ethynynl selenides and tellurides

Readily available selenium powder was chosen as an ideal selenium source to construct a series of bis(arylethynyl) selenium compounds in moderate to excellent yields through the activation of terminal alkyne C–H bond mediated by AgF. The reaction has the advantages of easy operation, good substrate scope and high atom economy. In addition, tellurium powder was also successfully applied to this system for the construction of bis(arylethynyl) tellurides under identical conditions.

Silver-Catalyzed Activation of Terminal Alkynes for Synthesizing Nitrogen-Containing Molecules.

Alkynes are one of the most abundant chemicals in organic chemistry, and therefore the development of catalytic reactions to transform alkynes into other useful functionalities is of great value. In recent decades, extraordinary advances have been made in this area with transition-metal catalysis, and silver-based reagents are ideal for the activation of alkynes. This high reactivity is probably due to the superior π-Lewis acidic, carbophilic behavior of silver(I), allowing it to selectively activate carbon-carbon triple bonds (C≡C) through the formation of a silver-π complex. Within this field, we have been interested in the activation and subsequent reactions of readily accessible terminal alkynes for the synthesis of nitrogen-containing compounds, which has generally received less attention than methods involving internal alkynes. This is possibly due to the lack of suitable reactive reaction partners that are compatible under transition metals. Therefore, a thorough understanding of the factors that influence homogeneous silver catalysis and the identification of the appropriate reaction partners can provide a powerful platform for designing more efficient silver-catalyzed reactions of terminal alkynes. In this context, we envisioned that using readily available, environmentally benign, and inexpensive trimethylsilyl azide (TMSN3) or an isocyanide as the nitrogen-donor would be the key to develop novel reactions of terminal alkynes.This Account describes our efforts since 2013 toward the development of novel silver-catalyzed tandem reactions of terminal alkynes with either TMSN3 or isocyanides for the assembly of various nitrogen-containing compounds. The first section of this Account discusses the initial developments in the silver-catalyzed hydroazidation of terminal alkynes with TMSN3 and the subsequent advances made in our laboratory. We first describe the discovery and experimental and computational mechanistic investigations of silver-catalyzed hydroazidation reactions, which is the most efficient strategy reported to date for accessing vinyl azides. Mechanistic study of this hydroazidation reaction provides an alternative activation mode for terminal alkyne conversion in transition metal catalysis. We then present the chemistry of in situ generated vinyl azides, including one-pot tandem radical addition/cyclization or migration reactions of terminal alkynes to access a variety of nitrogen-containing molecules. Finally, we discuss the one-pot, multistep tandem hydroazidation and 1,2-azide migratory gem-difluorination of terminal alkynes for the synthesis of β-difluorinated alkyl azides. The second section describes the silver-catalyzed coupling reactions between terminal alkynes and isocyanides, which offer a straightforward method for accessing synthetically useful building blocks, such as pyrroles, allenamides, benzofuran, vinyl sulfones, indazolines, propiolonitriles, and pyrazoles. The high efficiency, mild conditions, low cost, broad substrate scope, high chemo- and regioselectivity, step economy, and ecofriendliness of the developed approaches make them attractive and practical. The progress in this area provides guiding principles for designing new reactions of terminal alkynes that can be extended to various nitrogen-containing molecules of interest to medicinal and materials chemists.

Continuous Microwave-Assisted Synthesis of Silver Nanoclusters Confined in Mesoporous SBA-15: Application in Alkyne Cyclizations

Metal nanoclusters are becoming exciting candidates as highly efficient catalysts for heterogeneous processes in view of their extraordinary surface to volume ratio and the high concentration of uncoordinated atoms that contribute to enhanced catalytic activity. For this reason, the development of accurate and reliable procedures for the synthesis of stable and supported metal nanoclusters is highly desirable. Although Ag nanoclusters (Ag NCs) stabilized by anion templates with a structure like Agm+nm+ and a long lifetime have been widely investigated, supported clusters present significant advantages regarding their recovery and recyclability. In spite of their potential, the stabilization of clusters of precious metals on porous substrates is scarcely investigated. Herein, we present an innovative approach for the synthesis of stable Ag nanoclusters designed with the aim of achieving a strict control of key phases such as mixing, microwave heating, and quenching. The catalyst was used for the activation of alkynes showing excellent activity for the formation of C–O, C–N, and C–C bonds. When compared with commonly used homogeneous Ag salts, Ag NCs enhanced the catalytic activity toward the cyclization of a wide range of substrates, thereby minimizing the metal loading and allowing the separation as well as the reuse of the catalyst for multiple cycles.

Novel Glycosidation Based on Alkyne Activation

Novel Glycosidation Based on Alkyne Activation

Novel Glycosidation Based on Alkyne Activation

Novel Glycosidation Based on Alkyne Activation

Development of Magnesium Oxide-Silver Hybrid Nanocatalysts for Synergistic Carbon Dioxide Activation to Afford Esters and Heterocycles at Ambient Pressure.

Multi-metallic hybrid nancatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag0 nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO2 into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at % Ag) catalysts are synthesized by impregnating Ag+ ions in porous MgO cubes followed by reduction using NaBH4. Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ~100 nm (edge length) MgO cubes decorated with ~ 5 to 25 nm Ag0 NPs. Detailed XPS analysis illustrates Ag0 is present in two forms, <10 nm NPs and ~25 nm aggregates. The MgO@Ag-7 catalyst is effective for inserting CO2 into aryl alkynes followed by SN2 coupling with allylic chlorides to afford a wide range of ester and lactone heterocycles in excellent yields (61-93%) and with low E-factor (2.8). The proposed mechanism suggests a CO2 capture and substrate assembly role for 3D porous MgO while Ag0 performs the key activation of alkyne and CO2 insertion steps. The catalyst is recyclable (5x) with no significant loss of product yield. Overall, these results demonstrate viable approaches to hybrid catalyst development for challenging conversions such as CO2 utilization in a green and sustainable manner.