Ene Reaction Research Articles

Metal-Free Phosphate Modified Hierarchically Porous Carbon–Silica Nanocomposites for Solvent-Free Glycerol Carbonylation and Esterification Reactions

Metal-Free Phosphate Modified Hierarchically Porous Carbon–Silica Nanocomposites for Solvent-Free Glycerol Carbonylation and Esterification Reactions

Carbonylative Cross-Coupling Reaction of Allylic Alcohols and Organoalanes with 1 atm CO Enabled by Nickel Catalysis.

A nickel-catalyzed three-component carbonylative cross-coupling reaction of allylic alcohols and organoalanes with CO at atmospheric pressure is reported, enabling the expedient formation of β,γ-unsaturated ketones with broad scope. Particularly, the chemoselective allylic carbonylation of diols further highlights the practicability of this protocol. The leverage of organoalanes as both the coupling components and the activators for the alcohol functionalization is crucial for this method, thus no extraneous activators are required.

Switchable Radical Carbonylation by Philicity Regulation.

Carbonylation reactions involving CO as readily available C1 synthons have become one of the most important tools for the construction of carbonyl compounds from feedstock chemicals. Despite numerous catalytic methods for carbonylation reactions proceeding via ionic or radical pathways, an inherent limitation to these methods is the need to control switchable single and double carbonylative formation of value-added products from the same and simple starting materials. Here, we describe a new strategy that exploits photoredox catalysis to regulate the philicity of amine coupling partners to drive switchable radical carbonylation reactions. In double carbonylation, amines were first transformed into nitrogen radical cations by single-electron transfer-oxidation and coupled with CO to form carbamoyl radicals, which further underwent radical cross-coupling with the incipient cyanoalkyl acyl radicals to afford the double carbonylation products. Upon the addition of stoichiometric 4-dimethylaminopyridine (DMAP), DMAP competitively traps the initially formed cyanoalkyl acyl radical to form the relatively stabilized cyanoalkyl acyl-DMAP salts that engaged in the subsequent substitution with the nucleophilic amines to produce the single carbonylation products. The reaction proceeded smoothly with excellent selectivity in the presence of various amine nucleophiles at room temperature, generating valuable amides and α-ketoamides in a versatile and controlled fashion. Combined experimental and computational studies provided mechanistic insights into the possible pathways.

Synthesis of Thiomorpholine via a Telescoped Photochemical Thiol-Ene/Cyclization Sequence in Continuous Flow.

A procedure for the continuous flow generation of thiomorpholine in a two-step telescoped format was developed. The key step was the photochemical thiol–ene reaction of cysteamine hydrochloride and vinyl chloride as low-cost starting materials. This reaction could be conducted under highly concentrated (4 M) conditions using a low amount (0.1–0.5 mol %) of 9-fluorenone as the photocatalyst, leading to the corresponding half-mustard intermediate in quantitative yield. Thiomorpholine was subsequently obtained by base-mediated cyclization. The robustness of the process was demonstrated by performing the reaction for 7 h (40 min overall residence time), isolating the desired thiomorpholine via distillation.

Methanol-to-olefins catalysis on window-cage type zeolites/zeotypes with syngas co-feeds: Understanding syngas-to-olefins chemistry

Catalyst lifetime and product selectivity of methanol-to-olefins (MTO) catalysis on window-cage type zeolites and zeotypes are examined and interpreted to elucidate the critical role of high-pressure H2 and CO in MTO catalysis at conditions relevant for syngas-to-olefins (STO) conversion (H2/CH3OH >100, CO/CH3OH >100). Propylene co-feed experiments elucidate that acid-catalyzed hydrogenation reactions transpire and enhance olefins-cycle propagation by intercepting formaldehyde-mediated condensation and dehydrocyclization reaction cascades to result in an increase in catalyst lifetime (>7×) and decrease ethylene-to-propylene (∼1.5×) and ethylene-to-butenes ratios (∼1.6×) during MTO with high-pressure H2 co-feeds. CO is mechanistically relevant in increasing ethylene-to-propylene (∼1.5–3.0×) and ethylene-to-butenes ratio (∼1.7×) during MTO catalysis only at high CO (3–8 bar) and syngas pressures (24 bar, H2/CO∼2–16); at these high pressures, CO participates in carbonylation reactions to enhance aromatics-cycle propagation and enable a pathway for ethylene production via methyl acetate formation. These results suggest that high-pressure syngas introduces new catalytic pathways to distinguish MTO catalysis from STO catalysis and MTO catalysis in the presence of high-pressure syngas reagents.

A profound change from the classic mechanism of electrophilic aromatic substitution in the gas phase to a novel mechanism, including the hydride transfer in the presence of Cucurilbit[6] uril (DFT prediction)

The DFT B3LYP/6–311+G* calculations were carried out for the reactions ArH / CBr3+Al2Br7− (ArH = PhH, PhNH2, PhNMe2) (I) and ArH / CBr3+Al2Br7−/СО (II) in a gas phase. The same reactions in the presence of cucurbit[6]uril (CB6), were calculated by the DFT B3LYP/6–31G* basis set. The calculations show that the classical mechanism of electrophilic aromatic substitution (EAS) in the gas phase changes abruptly when the reactions are carried out in CB6. Unlike the classical mechanism involving the attack of electrophile on the arene C atom with the formation of the tetrahedral cationic intermediate followed by proton substitution by electrophile, in CB6, the cation attacks the arene H atom resulting in high barrier H / Br exchange (reaction I) or low-barrier carbonylation reaction (reaction II) as the only channel in each case.

A practical concept for catalytic carbonylations using carbon dioxide

The rise of CO2 in atmosphere is considered as the major reason for global warming. Therefore, CO2 utilization has attracted more and more attention. Among those, using CO2 as C1-feedstock for the chemical industry provides a solution. Here we show a two-step cascade process to perform catalytic carbonylations of olefins, alkynes, and aryl halides utilizing CO2 and H2. For the first step, a novel heterogeneous copper 10Cu@SiO2-PHM catalyst exhibits high selectivity (≥98%) and decent conversion (27%) in generating CO from reducing CO2 with H2. The generated CO is directly utilized without further purification in industrially important carbonylation reactions: hydroformylation, alkoxycarbonylation, and aminocarbonylation. Notably, various aldehydes, (unsaturated) esters and amides are obtained in high yields and chemo-/regio-selectivities at low temperature under ambient pressure. Our approach is of interest for continuous syntheses in drug discovery and organic synthesis to produce building blocks on reasonable scale utilizing CO2.

Nickel-Catalyzed Asymmetric Hydroaryloxy- and Hydroalkoxycarbonylation of Cyclopropenes.

The asymmetric Reppe carbonylation reactions provide a straightforward access to α-chiral carbonyl compounds. The reported paradigms predominantly adopted precious palladium as the catalyst. Here we report a nickel-catalyzed asymmetric carbonylation of cyclopropenes with phenyl formate and CO/ROH, respectively. This asymmetrical synthetic protocol features high atom economy, good functional group tolerance, which rapidly constructs polysubstituted cyclopropanecarboxylic derivatives with excellent diastereo- and enantioselectivity. The synthetic utility is demonstrated by facile conversion of the chiral products into bioactive molecules such as (-)-Tranylcypromine and (-)-Lemborexant.

Carbonylative Suzuki Coupling Catalyzed by Pd Complexes Based on [N,P]‐Pyrrole Ligands: Direct Access to 2‐Hydroxybenzophenones

AbstractThe Suzuki‐Miyaura cross‐coupling is one of the most useful synthetic tools to build C−C bonds, but the use of hydroxyaryl halides to direct access hydroxy‐byaryls still remains a challenge. For the carbonylative version of the reaction, the synthesis of hydroxybiaryl ketones is commonly solved by protecting group strategies. In this work, we report a protocol of carbonylative Suzuki‐ Miyaura coupling catalysed by a [N,P]‐PdCl2complex using aryl halides, various aryl boronic acids and CO. We were able at first to obtain biphenyls, finding a singular reactivity towards 2‐bromophenol, that later was extended to the carbonylation reaction, resulting in methodology that allows the obtention of 2‐hydroxybiaryl ketones, with a functional group tolerance toward amines, alkoxy, ketones, esters, and halides.magnified image

Nickel‐Catalyzed Asymmetric Hydroaryloxy‐ and Hydroalkoxycarbonylation of Cyclopropenes

The asymmetric Reppe carbonylation reactions provide a straightforward access to α-chiral carbonyl compounds. The reported paradigms predominantly adopted precious palladium as the catalyst. Here we report a nickel-catalyzed asymmetric carbonylation of cyclopropenes with phenyl formate and CO/ROH, respectively. This asymmetrical synthetic protocol features high atom economy, good functional group tolerance, which rapidly constructs polysubstituted cyclopropanecarboxylic derivatives with excellent diastereo- and enantioselectivity. The synthetic utility is demonstrated by facile conversion of the chiral products into bioactive molecules such as (−)-Tranylcypromine and (−)-Lemborexant.

Au Nanoparticles in Silsesquioxane-Based Hybrid Networks by Simultaneous Recovery and Reduction of Au(III) in Wastewater

The recovery of gold from wastewater or electronic waste is significant due to its enormous value in a variety of fields. An amine-functionalized silsesquioxane (SQ)-based hybrid network (PCS-PAA) was successfully synthesized through the cost-effective, mild amine–ene reaction of acrylate-functionalized SQ with triaminoethylamine (TAA). Hydrophilic PCS-PAA helps to adsorb Au(III) via the coordination with abundant heteroatoms (N and O). The adsorption capacity of PCS-PAA for Au(III) reaches 647 mg/g within 30 min at room temperature and 1235 mg/g at 323 K, respectively. The Langmuir model is more suitable to describe the adsorption process, and the pseudo-second-order model well fits the adsorption kinetic. Surprisingly, most Au(III) ions are in situ reduced to Au(0) particles, which are uniformly distributed on the surface of PCS-PAA. PCS-PAA-Au (PCS-PAA loaded with Au) can reduce 4-nitrophenol to 4-aminophenol with high catalytic activity. More interestingly, PCS-PAA can selectively adsorb Au(III) from e-waste. This work provides a convenient and mild method to recover Au(III) from wastewater or e-waste for multiple purposes.

Polymerization of Myrcene in Both Conventional and Renewable Solvents: Postpolymerization Modification via Regioselective Photoinduced Thiol-Ene Chemistry for Use as Carbon Renewable Dispersants.

Polymeric dispersants are useful materials used in many different industries and often derived from oil-based chemicals, for example, in automotive fluids so as to prevent particulates from precipitation and causing potential damage. These are very often polyisobutene derivatives, and there is a growing need to replace these using chemicals using renewable resources such as the use of naturally occurring myrcene. Polymyrcene (PMy), with an ordered microstructure, has been successfully synthesized via both anionic and radical polymerization in different solvents and subsequently subjected to functionalization via photoinduced thiol–ene click reactions with a number of thiols, methyl thioglycolate, 3-mercaptopropionic acid, 3-mercapto-1-hexanol, 2-mercaptoethanol, and 1-thioglycerol, using 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator under UV irradiation (λ = 365 nm) at ambient temperature. The polarity of the solvent has an important impact on the microstructure of the produced polymyrcene and, in particular, 1,2-unit (∼4%), 3,4-unit (∼41%), and 1,4-unit (∼51%) PMy were obtained via anionic polymerization in a polar solvent (THF) at ambient temperature, while 3,4-unit (∼6%) and 1,4-unit (∼94%, including cis and trans) PMy were obtained with cyclohexane as the solvent. Subsequently, photochemical thiol–ene reactions were carried out on the resulting PMy with different isomers exhibiting different reactivities of the double bonds. This strategy allows for the introduction of functional/polar groups (−COOH, −OH) into hydrophobic PMy in a controlled process. Hydrogenation of PMy and derivatized PMy was carried out to investigate any effects on the stabilities of the products which are desirable for many applications.

Structural characterization of polar melanoidins deriving from Maillard reaction intermediates – A model approach

Chemical conversions of reducing sugars and amino compounds induce the formation of heterogenous, high-molecular-weight colorants (‘melanoidins’) with widely unknown chemical structures. Model experiments of reactive intermediates have proven to be suitable for unravelling the formation mechanisms of colored reaction products. Here, the active methylene norfuraneol was selected and incubated individually as well as in combination with glyoxal, glycolaldehyde, and acetaldehyde at elevated temperatures. Photometric and chromatographic methods as well as mass spectrometry were used to analyze the colored reaction products and reveal the reactivity of different carbonyls regarding the formation of heterogenous oligomers. Aqueous solutions of norfuraneol and glyoxal exceeded the color formation of all other model reaction systems and it could be shown that the initial reactants as well as their degradation products were incorporated into the colorants. The colored oligomers described herein were composed of carbohydrate-based intermediates of the Maillard reaction and defined as melanoidin precursors or pre-melanoidins.

Synergistic oxidation of organic micropollutants by Mn(VII)/periodate system: Performance and mechanism

The increased release of various emerging organic contaminants into natural waters has posed great threats to ecological safety and public health. The ensuing global water contamination has necessitated the development of highly efficient treatment strategies for water purification. Herein, we presented for the first time that the combined utilization of permanganate (Mn(VII)) and periodate (PI) could synergistically and rapidly accomplish complete destruction of different organic micropollutants (e.g., bisphenol F, methotrexate, and tetracycline) within 2–5 min. Comparatively, the single treatment only eliminated very small amounts of micropollutants. Mechanistic investigations were performed using the trapper-based electron spin resonance, scavenging and probe experiments, UV–vis spectra analysis, determination of iodine species, and multiple validation tests. These data collectively suggested that the highly reactive Mn(V)/Mn(VI) intermediates played the leading role in accelerating contaminant abatement within the Mn(VII)/PI oxidation system. Reactive oxygen/or iodine species (1O2, OH, O2-, IO3, and IO4) and low valence Mn species (Mn(II), Mn(III), and in-situ formed MnO2 colloids) did not participate in decontamination in this process. Subsequently, the oxidized products of three micropollutants were determined, and the transformation pathways were clarified. Ring-opening, C-C bond cleavage, demethylation, carbonylation, and hydroxylation reactions mainly occurred in the degradation process. Notably, the combined system did not yield any toxic iodinated end products. Finally, the environmental risks of the degradation products were also evaluated based on in silico QSAR-based prediction tools. Overall, this study provides a novel, highly efficient, and green treatment technology, i.e., Mn(VII)/PI system, which could be employed for rapid and sustainable water decontamination.

Highly Selective Carbonylation of CH3Cl to Acetic Acid Catalyzed by Pyridine‐Treated MOR Zeolite

AbstractThe selective conversion of methane to high value‐added chemicals under mild conditions is of great significance for the commercially viable and sustainable utilization of methane but remains a formidable challenge. Herein, we report a strategy for efficiently converting methane to acetic acid via CH3Cl as an intermediate. Up to 99.3 % acetic acid and methyl acetate (AA+MA) selectivity was achieved over pyridine‐pretreated MOR (MOR‐8) under moderate conditions of 523 K and 2.0 MPa. Water, conventionally detrimental to carbonylation reaction over zeolite catalysts, was conducive to the production of AA in the current reaction system. In the 100 h continuous test with the MOR‐8 catalyst, the average AA+MA selectivity remained over 98 %. AA was formed by carbonylation of methoxy groups within 8‐membered rings of MOR followed by hydrolysis. This strategy provided an approach for highly efficient utilization of methane to oxygenates under mild reaction conditions.

Highly Selective Carbonylation of CH3 Cl to Acetic Acid Catalyzed by Pyridine-Treated MOR Zeolite.

The selective conversion of methane to high value-added chemicals under mild conditions is of great significance for the commercially viable and sustainable utilization of methane but remains a formidable challenge. Herein, we report a strategy for efficiently converting methane to acetic acid via CH3 Cl as an intermediate. Up to 99.3 % acetic acid and methyl acetate (AA+MA) selectivity was achieved over pyridine-pretreated MOR (MOR-8) under moderate conditions of 523 K and 2.0 MPa. Water, conventionally detrimental to carbonylation reaction over zeolite catalysts, was conducive to the production of AA in the current reaction system. In the 100 h continuous test with the MOR-8 catalyst, the average AA+MA selectivity remained over 98 %. AA was formed by carbonylation of methoxy groups within 8-membered rings of MOR followed by hydrolysis. This strategy provided an approach for highly efficient utilization of methane to oxygenates under mild reaction conditions.

The Sonogashira Carbonylation Reaction between Aromatic Bromide and Alkyne with N‐Formylsaccharin as a CO Source

AbstractThe carbonylative Sonogashira coupling reaction of aromatic bromide with terminal alkynes has been developed with N‐formylsaccharin as a CO source. The reaction, which has certain advantages in cost and safety of raw materials, is carried out in a simple and safe one‐pot method. A variety of alkynones with good functional group compatibility can be obtained in medium to high yields.

Intramolecular Propargylic Ene Reaction of Benzyne En Route to Highly Functionalized Allenes and Allenamides

AbstractA variety of highly functionalized allenes and allenamides are prepared by intramolecular propargylic ene reactions of benzynes. Specific benzyne precursors having a chlorodiisopropylsilyl group serve as platforms to link with various propargyl alcohols via a Si–O bond, thereby expanding the scope of this reaction. Also demonstrated is a complete transmission of point to axial chirality to give a chiral, non-racemic allenamide.

Novel approach to A-ring synthon for Pd-catalyzed synthesis of 1α-hydroxylated vitamin D metabolites

A novel approach to an A-ring synthon for Pd-catalyzed synthesis of 1α-hydroxylated vitamin D metabolites is described. Key step is an asymmetric glyoxylate ene reaction to access a highly diastereomerically pure α-hydroxy ester. Subsequent stereospecific transformation to an anti-1,3-diol and appropriate chemical modifications at both ends of the acyclic precursor leads to a diastereomerically and enantiomerically pure silylated anti-1,3-diol enyne, serving as a versatile A-ring synthon for its use in vitamin D synthesis.

Recyclable palladium-catalyzed cyclocarbonylation between benzyl chlorides and salicylic aldehydes towards coumarins

A novel and practical route to coumarin derivatives has been developed via the heterogeneous Pd-catalyzed carbonylative reaction and subsequent intramolecular condensation process starting from commercially easily available benzyl chlorides and salicylic aldehydes. Reactions were performed in the existence of 2 mol% of an SBA-15-immobilized bidentate phosphine palladium complex [SBA-15-P,P-PdCl2] in dioxane at 110 °C with Et3N as base under 10 bar of CO to afford a wide range of coumarin derivatives mostly with good to high yields. Importantly, this new heterogenized palladium complex was easy to recover via filtration of the reaction mixture, and was recyclable up to 8 times without apparent drop in its catalytic performance.