Hydration Of Alkynes Research Articles

L‐Cysteine‐Catalysed Hydration of Activated Alkynes

Hydration reactions consist of the introduction of a molecule of water into a chemical compound and are particularly useful to transform alkynes into carbonyls, which are strategic intermediates in the synthesis of a plethora of compounds. Herein we demonstrate that L‐cysteine can catalyse the hydration of activated alkynes in a very effective and fully regioselective manner to access important building blocks in synthetic chemistry such as β‐ketosulfones, amides and esters, in aqueous media. The mild reaction conditions facilitated the integration with enzyme catalysis to access chiral β‐hydroxy sulfones from the corresponding alkynes in a one‐pot cascade process in good yields and excellent enantiomeric ratios. These findings pave the way towards establishing a general method for metal‐free, cost‐effective, and more sustainable alkyne hydration processes.

L-Cysteine-Catalysed Hydration of Activated Alkynes.

Hydration reactions consist of the introduction of a molecule of water into a chemical compound and are particularly useful to transform alkynes into carbonyls, which are strategic intermediates in the synthesis of a plethora of compounds. Herein we demonstrate that L-cysteine can catalyse the hydration of activated alkynes in a very effective and fully regioselective manner to access important building blocks in synthetic chemistry such as β-ketosulfones, amides and esters, in aqueous media. The mild reaction conditions facilitated the integration with enzyme catalysis to access chiral β-hydroxy sulfones from the corresponding alkynes in a one-pot cascade process in good yields and excellent enantiomeric ratios. These findings pave the way towards establishing a general method for metal-free, cost-effective, and more sustainable alkyne hydration processes.

Gold Trifluoromethyl Complexes as Efficient Regioselective Catalysts in Alkyne Hydration.

Gold(III) complexes containing trifluoromethyl ligands are efficient catalysts in the hydration of alkynes, operating at low catalyst loadings, without additives, using environmentally friendly solvents and at mild conditions (60 °C). Hydration of terminal and internal alkynes provides the corresponding ketones in quantitative yields without special precautions as dry solvents or inert atmospheres. Remarkably, hydration of asymmetric internal alkynes proceeds with moderate to notable regioselectivities, providing mixtures of the two possible isomers with ratios up to 90 : 10.

Synthesis and Characterization of Transition Metal Complexes Supported by Phosphorus Ligands Obtained Using Hydrophosphination of Cyclic Internal Alkenes.

The design and study of rich, bulky phosphorus ligands is a key area of research for homogeneous catalysis. Here, we describe an original strategy using a hydrophosphination reaction to produce phosphines of interest for coordination chemistry and homogenous catalysis. In particular, the phosphine obtained by reacting diphenylphosphine with acenaphthylene (ligand 2) gives a ligand that adopts an unusual spatial geometry. The coordination chemistry of the ligand has been investigated with Au(I), Ag(I), Cu(I), and Pd(II), for which a complete characterization could be made, particularly in X-ray diffraction studies. The reactivity of some of these complexes has been demonstrated, particularly in Pd-catalyzed cross-coupling reactions and Au-catalyzed hydroaminations and in the hydration of alkynes.

Metal-Free, PPA-Mediated Fisher Indole Synthesis via Tandem Hydroamination-Cyclization Reaction between Simple Alkynes and Arylhydrazines.

A new variant of Fisher indole synthesis involving Bronsted acid-catalyzed hydrohydrazination of unactivated terminal and internal acetylenes with arylhydrazines is reported. The use of polyphosphoric acid alone either as the reaction medium or in the presence of a co-solvent appears to provide the required balance for activating the C-C triple bond towards the nucleophilic attack of the hydrazine moiety without unrepairable reactivity loss of the latter due to competing amino group protonation. Additionally, the formal hydration of acetylenes to the corresponding ketones occurs under the same conditions, making it an alternative approach for generating carbonyl groups from alkynes.

Enhanced catalytic performance in acetylene hydration: A novel Cu-based catalyst anchored via P-O bonds on a CN supporter

Despite various catalysts being developed for acetylene hydration, challenges persist in achieving optimal selectivity and stability. In this report, we present a catalyst featuring the active component Cu-O3P3 attached to a nitrogen-dispersed carbon carrier (Cu-O3P3/CN) by self-assembly. Over this catalyst, the acetaldehyde selectivity of 88.2 % for acetylene hydration could still be obtained at 126 h (T = 240°C, GHSV(C2H2) = 90 h-1 and VH2O/VC2H2 = 4). Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and X-ray Diffraction analyze that the employed preparation method thoroughly prevents the reduction of high-valent Cu during the fabrication process. The construction of the specific Cu-O3P3 active site structure has been demonstrated by X-ray absorption fine structure and X-ray photoelectron spectroscopy tests. Density functional theory calculations confirm active Cu sites are modified to a more electron-deficient state by constructing Cu-O-P sites. Furthermore, the doping of the carbon carrier with heteroatom nitrogen may theoretically lead to a reduction in the energy barrier associated with the formation of intermediates and the desorption of products, thereby potentially enhancing the overall catalytic performance. This study introduces a versatile methodology for designing and developing well-defined, carbon-nitrogen-supported Cu-based catalysts and a strategy for fine-tuning their catalytic characteristics.

Oxygen vacancies prompt the formation of hydrated hydroxyzinc in Zn-based catalysts to enhance acetylene hydration

Herein, the Zn-based catalysts with oxygen vacancies were obtained via the simple and effective method, and the oxygen-vacancy (Ov)-rich anatase TiO2 was as carrier, which was introduced oxygen-vacancy through heat treatment. The catalysts performance test results showed that the Zn/TiO2-300-10 with oxygen-vacancy (Ov)-rich exhibited excellent catalytic performance (acetylene conversion >89 % for 30 h) at the reaction temperature of 260 °C. Electron paramagnetic resonance spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the formation of oxygen-vacancy in treated TiO2 carriers. Subsequently, all the Zn-based catalysts were characterized by a series of characterization techniques. The results showed that the Zn/TiO2-300-10 catalyst with Ov-rich could produce more hydroxyl‑containing Zn species and improve Zn dispersion than that of the untreated Zn/c-TiO2 catalysts. Meanwhile, the DFT calculation results showed that, for the oxygen-vacancy-rich Zn-based catalysts, the OH− species from (ZnOH)+ species participated in acetylene hydration, thereby reducing the activation energy of acetylene hydration, and allowing the regeneration of (ZnOH)+ species via water cleavage. While, the reactant C2H2 was directly reacted with water dissociation with higher activation energy for the Zn/TiO2 catalyst without oxygen-vacancy. This study lays the foundation for further developing other Ov-rich carriers more suitable for Zn loading.

A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts.

A polysubstituted 3-aminoimidazo[5,1-b]oxazol-6-ium framework has been accessed from a new nitrenoid reagent by a two-step ynamide annulation and imidazolium ring-formation sequence. Metalation with Au(I), Cu(I) and Ir(I) at the C2 position provides an L-shaped NHC ligand scaffold that has been validated in gold-catalysed alkyne hydration and arylative cyclisation reactions.

A method to synthesize specific active Cu sites of single-atom catalysts with high stability for acetylene hydration

Single-atom catalysts (SACs) have received much attention in the realm of energy and catalytic conversion due to their maximum atomic efficiency. Herein, we report a cascade anchoring strategy for the preparation of a Cu-S1O2 species of single-atom catalyst attached to a carbon carrier containing P and S (Cu-S1O2 SA/CPS) with a content of 12.4 wt%. Over the Cu-S1O2 SA/CPS catalyst, the conversion of 95.8% and selectivity of 87.2% for acetylene hydration could still be achieved at 70 h (T = 200°C, GHSV(C2H2) = 90 h−1 and VH2O/VC2H2 = 4). X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) tests reveal that the Cu atoms of Cu-S1O2 SA/CPS are predominantly coordinated in a trinary manner (Cu-S1O2). Based on high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), it is demonstrated that the Cu single-atom sites are highly dispersed in Cu-S1O2 SA/CPS. It is evident from the scanning electron microscopy (SEM) that Cu-S1O2 SA/CPS has a two-dimensional layered structure. The specific structure of the active site Cu is primarily attributed to the coordination of S and O atoms, resulting in its superior stability for acetylene hydration towards the synthesis of acetaldehyde. Density functional theory (DFT) calculations confirm that the formation of the Cu-S1O2 site facilitates the activation of acetylene, which is a pivotal step in the acetylene hydration process and considered as the rate-determining step. This article not only introduces an innovative strategy in the synthesis of Cu SACs but also represents a significant breakthrough in the stability of Cu SACs in acetylene hydration.

A hybrid Au/Ru catalyst for sequential alkyne hydration/asymmetric transfer hydrogenation reactions

A hybrid catalytic system was developed for sequential alkyne hydration/asymmetric transfer hydrogenation reactions through the confinement of an amphiphilic polymer supported ruthenium and gold catalysts within core/shell silica gel.

Vinyl-pyrazole as a biomimetic acetaldehyde surrogate.

Inspired by the enzyme acetylene hydratase, we investigated the reactivity of acetylene with tungsten(II) pyrazole complexes. Our research revealed that the complex [WBr2(pz-NHCCH3)(CO)3] (pz = 3,5-dimethyl-pyrazolate) facilitates the stochiometric reaction between pzH and acetylene to give N-vinyl-pz. This vinyl compound readily hydrolyzes to acetaldehyde, mirroring the product of acetylene hydration in the enzymatic process. The formation of the vinyl compound likely involves a reactive intermediate complex where acetylene acts as a two-electron donor, in contrast to isolable acetylene complexes that are inert to nucleophilic attack by water. Results suggest an alternative mechanism for the enzyme, including vinylation of a neighboring amino acid by acetylene in the active site prior to hydration.

Carbon-supported Zn-HPW ligand catalysts for acetylene hydration

The Zn-HPW/AC catalyst effectively improves acidic sites and active metals dispersion. Zn–OH is the first to participate in the reaction, followed by the OH attacked acetylene, and the catalyst is reduced by H and participates in the cycle.

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF3: the case of alkyne hydration. Chemistry vs electrochemistry.

In order to replace the expensive metal/ligand catalysts and classic toxic and volatile solvents, commonly used for the hydration of alkynes, the hydration reaction of alkynes was studied in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) adding boron trifluoride diethyl etherate (BF3·Et2O) as catalyst. Different ionic liquids were used, varying the cation or the anion, in order to identify the best one, in terms of both efficiency and reduced costs. The developed method was efficaciously applied to different alkynes, achieving the desired hydration products with good yields. The results obtained using a conventional approach (i.e., adding BF3·Et2O) were compared with those achieved using BF3 electrogenerated in BMIm-BF4, demonstrating the possibility of obtaining the products of alkyne hydration with analogous or improved yields, using less hazardous precursors to generate the reactive species in situ. In particular, for terminal arylalkynes, the electrochemical route proved to be advantageous, yielding preferentially the hydration products vs the aldol condensation products. Importantly, the ability to recycle the ionic liquid in subsequent reactions was successfully demonstrated.

Water as a key ingredient in the synthesis of platinum H‐phosphonate complexes and catalytic cascade reactions involving the hydration of alkynes and hydrogen/deuterium exchange reaction

Several platinum (II) complexes bearing heteroatom‐substituted phosphine oxides ligand H(O)P(OCMe2CMe2O) were obtained. The H‐phosphonate was synthesized in an alternative, one‐pot procedure with the use of water from hexamethylphosphorus triamide and pinacol. In the presence of H(O)P (OCMe2CMe2O) ligand, [PtCl2(cod)] was converted into three new complexes: [PtCl2{P(OH)(OCMe2CMe2O)}2] [Pt1], [PtCl{P(O)(OCMe2CMe2O)}{P(OH)(OCMe2CMe2O)}2] [Pt2], and [Pt{P(OH)(OCMe2CMe2O)}4]Cl2 [Pt3]. When [PtCl2(PPh3)2] was utilized as the substrate, [PtCl(PPh3)2{P(OH)(OCMe2CMe2O)}]Cl [Pt4] and [PtCl(PPh3)2{P(O)(OCMe2CMe2O)}] [Pt5] complexes were obtained, as the results of reaction with H(O)P(OCMe2CMe2O) and HP(OCMe2CMe2O)(OCH2CMe2NH) ligands. The structural features of all complexes were characterized by physicochemical and spectroscopic methods as well as single X‐ray diffraction studies. Complex [Pt1] was found to promote cascade reaction, the addition of water to triple bond, and hydrogen/deuterium exchange reaction. The hydration reaction of substituted terminal aryl alkynes gave exclusively Markovnikov products and tolerated different functional groups. Various aryl ketones were synthesized in good to excellent yield. H/D exchange reaction was exemplified by the model reaction of acetophenone in deuterium containing methanol. Factors influencing the effectiveness of the hydrogen/deuterium exchange reaction of the methyl group were determined. The cascade procedure bears the potential to overcome the limitations of conventional synthesis and unlocks practical use in the synthesis of deuterium‐labeled pharmaceuticals.

Experimental and Theoretical Investigation of Ion Pairing in Gold(III) Catalysts.

The ion pairing structure of the possible species present in solution during the gold(III)-catalyzed hydration of alkynes: [(ppy)Au(NHC)Y]X2 and [(ppy)Au(NHC)X]X [ppy = 2-phenylpyridine, NHC = NHCiPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; NHC = NHCmes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene X = Cl-, BF4-, OTf-; Y = H2O and 3-hexyne] are determined. The nuclear overhauser effect nuclear magnetic resonance (NMR) experimental measurements integrated with a theoretical description of the system (full optimization of different ion pairs and calculation of the Coulomb potential surface) indicate that the preferential position of the counterion is tunable through the choice of the ancillary ligands (NHCiPr, NHCmes, ppy, and Y) in [(ppy)Au(NHC)(3-hexyne)]X2 activated complexes that undergo nucleophilic attack. The counterion can approach near NHC, pyridine ring of ppy, and gold atom. From these positions, the anion can act as a template, holding water in the right position for the outer-sphere attack, as observed in gold(I) catalysts.

FeIII -Based Eutectic Mixtures as Multi-task and Reusable Reaction Media for Efficient and Selective Conversion of Alkynes into Carbonyl Compounds.

Invited for the cover of this issue is the group of Vicente del Amo, Alejandro Presa Soto and Joaquín García-Álvarez (QuimSinSos Group) at the University of Oviedo. The image depicts the use of the FeIII -based deep eutectic mixture [FeCl3 ⋅6 H2 O/Gly (3:1)] (Gly = glycerol) as both promoter and solvent for the straightforward and selective hydration of alkynes, working under mild (45 °C), bench-type reaction conditions (air) and in the absence of ligands, co-catalysts or co-solvents. Read the full text of the article at 10.1002/chem.202301736.

Stereoselective Synthesis of Pyrrolo/Pyrido[2,1-a]isoindoles via Alkyne Iminium Ion Cyclization of Vinylogous Carbamates.

An efficient, acid-mediated, intramolecular alkyne iminium ion cyclization of oxoisoindolidene for the diastereoselective synthesis of pyrrolo/pyridoisoindole is described. This protocol features broad substrate scope and easy scalability. An unusualNtoC-1,3-alkyl shift is observed with substrates bearing strong electron donating group at the phenyl ring attached to alkyne with concomitant hydration of alkyne to the ketone.

Fe(III)-based Eutectic Mixtures as Multi-Task and Reusable Reaction Media for Efficient and Selective Conversion of Alkynes into Carbonyl Compounds.

An efficient, simple and general protocol for the selective hydration of terminal alkynes into the corresponding methyl ketones was developed by using a cheap, easy-to-synthesise and sustainable Fe(III)-based eutectic mixture [FeCl3·6H2O/Gly (3:1)] as both promoter and solvent for the hydration reaction, working: i) under mild (45 ºC) and bench type reaction conditions (air); and ii) in the absence of ligands, co-catalysts, co-solvents or toxic, non-abundant and expensive noble transition metals (Au, Ru, Pd). When the final methyl ketones are solid/insoluble in the eutectic mixture, the hydration reaction takes place in 30 minutes and the obtained methyl ketones can be isolated just by simple decantation of the liquid Fe(III)-DES, allowing the direct isolation of the desired ketones without VOC solvents. By using this straightforward and simple isolation protocol, we have been able to recycle our Fe(III)-based eutectic mixture system up to 8 consecutive times. Furthermore, our Fe(III)-eutectic mixture is able to promote the selective and efficient formal oxidation of internal alkynes into 1,2-diketones, being the system recycled up to 3 consecutive times. Preliminary investigations on a possible mechanism for the oxidation of the internal alkynes seems to indicate that it proceeds through the formation of the corresponding methyl ketones and α-chloroketones.

A Bimetallic Porphyrin Metal Organic Framework as Multifunctional Catalysts for CO2 Cycloaddition and Alkyne Hydration

AbstractHere, a post synthetic modification strategy is presented to prepare multifunctional Bi−MOF−Co by introducing Co atom into the porphyrin units of bismuth‐porphyrin metal organic framework (Bi−MOF). Under milder conditions (0.1 MPa, 80 °C), CO2 cycloaddition is achieved to form cyclic carbonate in 96 % yield catalyzed by Bi−MOF−Co. The recyclability of catalysts is confirmed by five cycle experiments without loss of activity. Moreover, alkyne hydration is also catalyzed by Bi−MOF−Co in 99 % yield. The hydration protocol exhibites excellent functional group compatibility.

Hydration of Unsymmetrical Internal Alkynes: Factors Governing the Regioselectivity

Hydration of Unsymmetrical Internal Alkynes: Factors Governing the Regioselectivity