Alkyne Insertion Research Articles

Mechanism exploring of acetylene hydrochlorination using hexamethylenetetramine as a single active site metal-free catalyst

An activated carbon (AC) supported hexamethylenetetramine (HMT), with a single tertiary amine N active site, was proposed to be used as a novel metal-free catalyst for acetylene hydrochlorination reaction. The 25% HMT/AC catalyst provided acetylene conversion of ~60% and C2H3Cl selectivity above 99% at 220 °C with a gas hourly space velocity (GHSV) of 30 h−1. X-ray photoelectron spectra suggested the tertiary amine nitrogen was the only N species in the catalysts. Theoretical calculations and experimental studies showed that HCl is adsorbed by HMT preferentially. The insertion of acetylene into ClH bond of HCl is the key step.

Pd-Catalyzed Synthesis of Densely Functionalized Cyclopropyl Vinyl Sulfides Reveals the Origin of High Selectivity in a Fundamental Alkyne Insertion Step

Catalytic atom-economic hydrothiolation of cyclopropyl acetylenes was developed. Using Pd/NHC complex as a precatalyst, regioselective addition of thiols to cyclopropyl acetylenes was successfully ...

Cobalt-Catalyzed Markovnikov Selective Sequential Hydrogenation/Hydrohydrazidation of Aliphatic Terminal Alkynes.

Here, we reported for the first time a mechanistically distinctive cobalt-catalyzed Markovnikov-type sequential semihydrogenation/hydrohydrazidation of aliphatic terminal alkynes in one pot. A cobalt hydride species was employed as two roles for both a unique metal-catalyzed Markovnikov-type insertion of the aliphatic terminal alkynes and then metal-catalyzed hydrogen atom transfer of alkenes. This operationally simple protocol exhibits excellent functional group tolerance and step economy. The hydrazone products could be easily transferred to various valuable amine derivatives.

Rh(III)‐Catalyzed Redox‐Neutral Cascade Annulation of Benzamides withp‐Quinone Methides

Herein, we demonstrate a [RhCp*Cl2]2catalyzed synthesis of isoindolo[2,1‐b]isoquinolin‐5(7H)‐one derivatives fromN‐(pivaloyloxy)benzamides andp‐quinone methides under redox neutral conditions.p‐Quinone methide derivatives were engaged for the first time as precursors in C–H activation reactions and the cascade sequence consists of Rh(III)‐catalyzed C–H activation, alkyne insertion followed by an intramolecular 1,6‐conjugate addition. This novel tandem reaction strategy offers a rapid and straightforward access to complex fused isoquinolinone derivatives in an efficient manner.

O-Carboranyl silane modified cellulose nanopaper prepared via in-situ coupling reaction

Cellulose Nanopaper is a kind of green material prepared from renewable cellulose nanofibrils. In order to achieve multi-functionization of cellulose nanopaper, thermally stable o-carborane moieties were introduced and grafted on the surface of cellulose nanopaper through silane coupling process. Firstly, o-carboranyl silane was designed and synthesized through alkyne insertion, oxidation and esterification reactions. Then o-carboranyl silane modified cellulose nanopaper was prepared via in-situ coupling and polycondensation reaction between o-carboranyl silane and cellulose nanopaper. The obtained nanopaper shows superhydrophobicity together with good transparency and flexibility. Besides, it exhibits improved dimensional stability and thermal stability owing to the introduction of o-carborane moiety.

Mechanism of Palladium‐Catalyzed Spiroannulation of Naphthols with Alkynes: A Density Functional Theory Study

The Cover Feature shows ortho-bromophenylnaphthalenols and acetylene substrates that, just like the fish in the sea, jump through an energy barrier to achieve the spiroannulation product. In their Full Paper, X. Luo et al. performed DFT calculations to investigate the mechanism and enantioselectivity of Pd-catalyzed spiroannulation of ortho-bromophenylnaphthalenols with acetylenes to achieve asymmetric dearomatization. They propose that the catalytic cycle is composed of an oxidative addition of the aryl bromide to Pd(0) to afford an aryl palladium species, followed by acetylene insertion into the Pd–C(aryl) bond, Pd-assisted intramolecular deprotonation of the naphthol moiety and reductive elimination to give the spiroannulation product. They found that both the rate- and enantioselectivity-determining steps are acetylene insertion, and explained that the enantioselectivity is controlled by the steric repulsion between the naphthol moiety and the ligand. More information can be found in the Full Paper by X. Luo et al.

Palladium-Catalyzed Carbonylative Annulation of 1-Hydroxy-o-Carborane and Internal Alkynes via Regioselective B-H Activation.

A Pd-catalyzed three-component carbonylative-annulation of 1-hydroxy-o-carborane, internal alkyne and carbon monoxide has been achieved via direct and regioselective cage B-H activation. A class of C,B-substituted carborano-coumarin derivatives with potential applications in pharmaceuticals were facilely prepared in moderate to high yields with excellent chemoselectivity and regioselectivity. A plausible reaction mechanism including CO insertion, electrophilic B-H metalation, alkyne insertion and reductive elimination was proposed.

Mechanism of Palladium‐Catalyzed Spiroannulation of Naphthols with Alkynes: A Density Functional Theory Study

AbstractPd‐catalyzed spiroannulation of bromophenylnaphthalenols with acetylenes to achieve asymmetric dearomatization is a powerful way to construct chiral spiro‐compounds. DFT calculations with the M06 functional have been performed to reveal the mechanism and enantioselectivity of this reaction. After reversible oxidative addition of aryl bromide to Pd(0), acetylene insertion into the Pd−C(aryl) bond is considered to be the rate‐ and enantioselectivity determining step. Subsequent deprotonation and reductive elimination then give the spiroannulation product. The overlay and noncovalent interaction analysis of the critical transition states were used to reveal the origin of the enantioselectivity for this reaction. We found that the axial chirality of the naphthol moiety affects the relative free energies of the corresponding transition states, whereas the enantioselectivity is controlled by the steric repulsion between the naphthol moiety and the ligand.

Graphene oxide-wrapped sulfur/acetylene black for high-performance lithium-sulfur batteries

GO@S/C composite with a multilayered sandwich structure was prepared by a moderate sol-gel method, which was based on porous acetylene black (C) loading sulfur and insertion into multilayered graphene oxide (GO). When evaluated as a cathode for lithium-sulfur batteries (LSBs), it shows an improved capacity of 1433 mAh/g at 0.1 C and 433 mAh/g at 5 C with almost 100% coulombic efficiency for comparison with pure sulfur electrode. It also effectively hinders the expansion of sulfur, the dissolution of polysulfides, and the shuttle effect due to the adsorption and local confinement of polysulfide by porous C and GO.

Rhodium(III)-Catalyzed Atroposelective Synthesis of Biaryls by C-H Activation and Intermolecular Coupling with Sterically Hindered Alkynes.

Reported herein is the atroposelective synthesis of biaryl NH isoquinolones by RhIII -catalyzed C-H activation of benzamides and intermolecular [4+2] annulation for a broad scope of 2-substituted 1-alkynylnaphthalenes, as well as sterically hindered, symmetric diarylacetylenes. The axial chirality is constructed based on dynamic kinetic transformation of the alkyne in redox-neutral annulation with benzamides, with alkyne insertion being stereodetermining. The reaction accommodates both benzamides and heteroaryl carboxamides and proceeds in excellent regioselectivity (if applicable) and enantioselectivities (average 91.8 % ee). An enantiomerically and diastereomerically pure rhodacyclic complex was prepared and offers insight into enantiomeric control of the coupling system, wherein the steric interactions between the amide directing group and the alkyne substrate dictate both the regio- and enantioselectivity.

Rhodium(III)‐Catalyzed Atroposelective Synthesis of Biaryls by C−H Activation and Intermolecular Coupling with Sterically Hindered Alkynes

AbstractReported herein is the atroposelective synthesis of biaryl NH isoquinolones by RhIII‐catalyzed C−H activation of benzamides and intermolecular [4+2] annulation for a broad scope of 2‐substituted 1‐alkynylnaphthalenes, as well as sterically hindered, symmetric diarylacetylenes. The axial chirality is constructed based on dynamic kinetic transformation of the alkyne in redox‐neutral annulation with benzamides, with alkyne insertion being stereodetermining. The reaction accommodates both benzamides and heteroaryl carboxamides and proceeds in excellent regioselectivity (if applicable) and enantioselectivities (average 91.8 %ee). An enantiomerically and diastereomerically pure rhodacyclic complex was prepared and offers insight into enantiomeric control of the coupling system, wherein the steric interactions between the amide directing group and the alkyne substrate dictate both the regio‐ and enantioselectivity.

Rh(III)-Catalyzed Domino [4 + 2] Annulation/Aza-Michael Addition of N-(Pivaloyloxy)benzamides with 1,5-Enynes via C-H Activation: Synthesis of Functionalized Aromathecins.

Reported herein are the Rh(III)-catalyzed cascade annulation reactions of N-(pivaloyloxy)benzamides with 1,5-enynes to access diversely substituted aromathecin derivatives involving C-H activation. The developed procedure offers an efficient synthetic tool for the assembly of a wide range of N-(pivaloyloxy)benzamides and 1,5-enynes with good atom economy and functional group tolerance. The key reactions involved in this annulation are alkyne insertion and aza-Michael addition under oxidant-free mild reaction conditions.

Construction of 1-Tetralols Bearing Two Contiguous Quaternary Chiral Centers through a Rhodium-Catalyzed Enantioselective Desymmetrization Cascade Reaction.

A novel and efficient access to polyfunctionnalized chiral 1-tetralols, bearing two contiguous quaternary carbon stereocenters, has been developed from various and easily accessible alkynyl-1,3-diketones, through a cascade process including a regioselective alkyne insertion, a 1,4-Rh shift, and a nucleophilic addition step via the desymmetrization of the 1,3-diketone moiety thanks to an appropriate rhodium-chiral diene complex in the presence of arylboronic acids.

Synthesis of Benzo[b]thiophenes through Rhodium‐Catalyzed Three‐Component Reaction using Elemental Sulfur

AbstractA benzo[b]thiophene synthesis by Rh‐catalyzed three‐component coupling reaction of arylboronic acids, alkynes, and elemental sulfur (S8) is developed. A notable feature of this protocol is that the thienannulation (thiophene annulation) proceeds with high regioselectivity via the sequential alkyne insertion, C−H activation, and then sulfur atom transfer to the metallacycle intermediate. In a similar manner, dibenzothiophenes can be synthesized from the parent biarylboronic acids and S8.magnified image

Cobalt(III)‐Catalyzed Synthesis of Fused Quinazolinones by C–H/N–H Annulation of 2‐Arylquinazolinones with Alkynes

A convenient and efficient CoIII‐catalyzed cyclization of 2‐arylquinazolinones with alkynes is described. The electron donating as well as withdrawing groups and also halide substituted quinazolinones are compatible with this reaction. This catalytic reaction is highly regioselective with unsymmetrical alkynes. A possible mechanism, involves a formation of five‐membered metallacycle I by metal‐catalyzed aromatic C–H bond activation, alkyne insertion, seven‐membered metallacycle intermediates followed by reductive elimination to give a final product.

Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes: a theoretical study.

Polycyclic compounds having biological activities can be modified by employing different substituents. Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes was investigated by using density functional theory calculations. A mechanistic study revealed that all the three reactions, A (Z = Me, X = tBu), B (Z = Me, X = Me), and C (Z = H, X = Me), underwent initial oxidative cyclization, from which the divergent cycloisomerization was triggered when different substituents were employed. It was found from our calculations that reactions A and B underwent alkyne insertion into the Rh-C(sp2) bond and resulted in a key metal carbenoid intermediate. From the metal carbenoid species, reaction A bearing a more hindered tert-butyl group prefers 1,2-hydrogen migration to produce a 6/5/4 tricyclic product, while reaction B bearing a less hindered methyl group prefers 1,2-carbon migration leading to ring expansion and producing a 6/5/5 tricyclic product. The origins of the distinct selectivity were disclosed, which are beneficial for the development of novel related reactions. For reaction C (Z=H, Z=H or Z=H, Z=Me), the β-hydrogen elimination was found to be favored over the alkyne insertion into the Rh-C(sp2) bond and thus the monocyclic product is delivered. The E/Z effects involved in the above two cases were also discussed.

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.

Visible light driven generation and alkyne insertion reactions of stable bis-cyclometalated Pt(iv) hydrides.

Hydride complexes resulting from the oxidative addition of C–H bonds are intermediates in hydrocarbon activation and functionalization reactions. The discovery of metal systems that enable their direct formation through photoexcitation with visible light could lead to advantageous synthetic methodologies. In this study, easily accessible dimers [Pt2(μ-Cl)2(C^N)2] (C^N = cyclometalated 2-arylpyridine) are demonstrated as a very convenient source of Pt(C^N) subunits, which promote photooxidative C–H addition reactions with different 2-arylpyridines (N′^C′H) upon irradiation with blue light. The resulting [PtH(Cl)(C^N)(C′^N′)] complexes are the first isolable Pt(iv) hydrides arising from a cyclometalation reaction. A transcyclometalation process involving three photochemical steps is elucidated, which occurs when the C^N ligand is a monocyclometalated 2,6-diarylpyridine, and a detailed analysis of the photoreactivity associated with the Pt(C^N) moiety is provided. Alkyne insertions into the Pt–H bond of a photogenerated Pt(iv) hydride are also reported as a demonstration of the ability of this class of compounds to undergo subsequent organometallic reactions.

Ruthenium-catalyzed cascade C-H activation/annulation of N-alkoxybenzamides: reaction development and mechanistic insight.

A highly selective ruthenium-catalyzed C–H activation/annulation of alkyne-tethered N-alkoxybenzamides has been developed. In this reaction, diverse products from inverse annulation can be obtained in moderate to good yields with high functional group compatibility. Insightful experimental and theoretical studies indicate that the reaction to the inverse annulation follows the Ru(ii)–Ru(iv)–Ru(ii) pathway involving N–O bond cleavage prior to alkyne insertion. This is highly different compared to the conventional mechanism of transition metal-catalyzed C–H activation/annulation with alkynes, involving alkyne insertion prior to N–O bond cleavage. Via this pathway, the in situ generated acetic acid from the N–H/C–H activation step facilitates the N–O bond cleavage to give the Ru-nitrene species. Besides the conventional mechanism forming the products via standard annulation, an alternative and novel Ru(ii)–Ru(iv)–Ru(ii) mechanism featuring N–O cleavage preceding alkyne insertion has been proposed, affording a new understanding of transition metal-catalyzed C–H activation/annulation.

Rh(III)-Catalyzed Coupling of Acrylic Acids and Ynenones via Olefinic C-H Activation and Michael Addition.

Rh(III)-catalyzed coupling between acrylic acids and yndienones has been realized for the synthesis of cis-hydrobenzofuranone. The reaction proceeded in excellent regio- and stereoselectivity under mild and redox-neutral conditions via a sequence of carboxylic acid-directed olefinic C-H activation, alkyne insertion, and Michael addition. Representative products were found to exhibit cytotoxicity toward the A549 cancer cell line at micromolar levels.