Reaction Of Ethers Research Articles

Accelerating the discovery of alkyl halide-derived natural products using halide depletion.

Even in the genomic era, microbial natural product discovery workflows can be laborious and limited in their ability to target molecules with specific structural features. Here we leverage an understanding of biosynthesis to develop a workflow that targets the discovery of alkyl halide-derived natural products by depleting halide anions, a key biosynthetic substrate for enzymatic halogenation, from microbial growth media. By comparing the metabolomes of bacterial cultures grown in halide-replete and deficient media, we rapidly discovered the nostochlorosides, the products of an orphan halogenase-encoding gene cluster from Nostoc punctiforme ATCC 29133. We further found that these products, a family of unusual chlorinated glycolipids featuring the rare sugar gulose, are polymerized via an unprecedented enzymatic etherification reaction. Together, our results highlight the power of leveraging an understanding of biosynthetic logic to streamline natural product discovery.

Control of thermal and mechanical properties by double-cyclopolymerization and copolymerization of trifunctional POSS with varying organic substituents

Abstract Phenyl- and trifluoropropyl-substituted corner-opening type cage silsesquioxane (CO-POSS) monomers capped with methacrylethoxypropyldimethylsiloxy groups at the three silanol moieties were prepared by the hydrosilylation of trisdimethylsilyl-capped heptaphenyl- and heptatrifluoropropyl-substituted trisilanols with ethylene glycol monoallyl ether and subsequent reaction with methacryloyl chloride. Reversible addition-fragmentation chain transferpolymerization was performed on these monomers, and their structures and properties were compared to those of their previously-reported isobutyl-substituted counterparts. The polymer with a phenyl group exhibited enhanced thermal and mechanical properties, whereas the polymer with a trifluoropropyl group exhibited not only water repellency but also oil repellency. In addition, trifunctional CO-POSS monomers with different organic substituents could be used for double-cyclocopolymerization, and tuning of their properties was achieved. Furthermore, the trifunctional CO-POSS monomer could be used for double-cyclocopolymerization with methyl methacrylate without cross-linking.

The aging mechanism of asphalt aromatics based on density functional theory, Frontier Orbitals, IR, SARA, and GPC

To investigate the effect of ·OH radicals on asphalt Aromatics aging, density functional theory was utilized to calculate the Gibbs free energy, reaction energy barrier, and temperature associated with asphalt aromatic decomposition, thermal oxygen aging, and UV aging. To study chemical structural activity, Frontier Orbitals theory and Fukui Functions were employed to determine Frontier Molecular Orbitals and Fukui Index. The findings reveal that the activity of aromatic compounds is primarily concentrated near the naphthalene ring, which is prone to etherification reactions. The alkyl activity of aromatic compounds is quite low, rendering them less susceptible to nucleophilic, electrophilic, and radicals' reactions. One reason for thermal oxygen aging of asphalt is the direct interaction between asphalt molecules and O2. On the other hand, UV aging occurs due to the splitting of O2 into ·O radicals, which in turn generate ·OH radicals which can oxidize asphalt. The results of quantum chemical calculations were cross-validated by infrared spectroscopy IR, SARA, and GPC methods. IR spectroscopy analysis showed that thermal and ultraviolet aging would increase carbonyl and benzene derivatives in aromatic compounds, while thermal aging would not increase hydroxyl groups. SARA further confirmed that asphalt aging would enhance molecular polarity. GPC confirmed that The molecular weight of asphalt aromatic components increases after aging. This article provides useful experience for using quantum chemistry to study the mechanism of asphalt aging.

Impact of thermal ethylene degradation in zeolite-templated carbon synthesis

Which is the best temperature for the synthesis of Zeolite-Templated Carbons (ZTCs)? This is the question which will be foregrounded in the present article. ZTCs were achieved using ethylene on protonic beta zeolite at different synthesis temperatures comprised between 490 and 890 °C. By comparing the results achieved from TGA, nitrogen physisorption at 77 K, XRD and XPS, an optimal ZTC synthesis temperature could be determined. For low temperature synthesis (i.e. 490 °C), textural defects arise in the carbon network, possibly related to the low reactivity of ethylene. At temperatures above 700 °C thermally induced ethylene transformation was evidenced, leading to the development of carbon species on the external surface of the zeolite and hence to the generation of composite materials. Below 700 °C, ZTC formation exclusively proceeds through a zeolite acid-site catalyzed mechanism, whilst with increasing temperature the thermally induced ethylene transformation path gains impact. We further prove that ZTC/turbostratic carbon composites can be achieved through a purely thermally induced ethylene transformation path by using an all-silica beta zeolite as template.

Design, Synthesis and Antitumor Activity of Quercetin Derivatives Containing a Quinoline Moiety.

Quercetin is a flavonoid with significant biological and pharmacological activity. In this paper, quercetin was modified at the 3-OH position. Rutin was used as a raw material. We used methyl protection, Williamson etherification reactions, and then substitution reactions to prepare 15 novel quercetin derivatives containing a quinoline moiety. All these complexes were characterized by 1H NMR, 13C NMR, IR and HRMS. Of these, compound 3e (IC50 = 6.722 μmol·L-1) had a better inhibitory effect on human liver cancer (HepG-2) than DDP (Cisplatin) (IC50 = 26.981 μmol·L-1). The mechanism of the action experiment showed that compound 3e could induce cell apoptosis.

Visible-light-induced three-component reactions of α-diazoesters, quinazolinones and cyclic ethers toward quinazoline-based hybrids.

An effective approach for the construction of 4-short-chain ether attached carbonyl group-substituted quinazolines was developed. Visible-light-induced three-component reactions of α-diazoesters, quinazolinones, and cyclic ethers, with a broad substrate scope and excellent functional group tolerance, under extremely mild conditions without the need for any additional additives and catalysts, selectively led to quinazoline-based hybrids in good to excellent yields. The synthesized hybrids, which are a conglomeration of a quinazoline, a short-chain ether, and a carbonyl group in one molecular skeleton, have potential for application in the development of new drugs or drug candidates.

Synthesis of ethyl furfuryl ether via etherification of furfuryl alcohol with ethanol over montmorillonite K10.

Ethyl furfuryl ether (EFE), which is synthesized via etherification of furfuryl alcohol (FFalc) with ethanol over Brønsted acid catalysts, is used as an additive in gasoline to reduce its consumption and CO2 emission. In this work, we demonstrate that the performance of this synthesis route can be improved by using commercially available, low-cost, and environmentally friendly montmorillonite K10, which produces EFE in a relatively high yield of 45.3% and a FFalc conversion of 94.2% at a low reaction temperature of 393 K within 1 h. Other commercially available clay minerals showing Brønsted acidity, namely, kaolinite and halloysite, were also used in the etherification reaction under identical conditions. The catalytic performance followed the order of montmorillonite K10 > halloysite > kaolinite, which is consistent with that of the Brønsted acidities determined via acid-base titration. The spent montmorillonite K10 showed a catalytic performance comparable to that of the fresh catalyst after calcination.

Asymmetric dearomatization of benzyl 1-naphthyl ethers via [1,3] O-to-C rearrangement.

A catalytic asymmetric dearomatization reaction of benzyl 1-naphthyl ethers accelerated by a chiral N,N'-dioxide/Co(II) complex is disclosed. The reaction proceeds via an enantioselective [1,3] O-to-C rearrangement through a tight ion-pair pathway, providing a wide array of α-naphthalenone derivatives bearing an all-carbon quaternary center in high yields with excellent ee values.

Photochemical α-amination of carbonyl groups with iodinanes.

We report on a photochemical reaction of silyl enol ethers with iminoiodinanes. This aza Rubottom reaction provides a direct access towards α-amino carbonyl compounds under catalyst free reaction conditions with light as the sole source of energy. Control experiments suggest the participation of triplet nitrene intermediates.

Synthesis of benzooxepane-fused cyclobutene derivatives via Pd-catalyzed cascade reactions of haloarenes and diynylic ethers.

A tandem palladium-catalyzed Sonogashira coupling, propargyl-allenyl isomerization, and [2+2] cycloaddition sequence between electron-deficient haloarenes and 1,8-diynylic ethers is developed. The reaction shows good functional tolerance and proceeds under mild conditions to provide a new profile of benzooxepane-fused cyclobutene derivatives in moderate to high yields with high selectivity. The reaction mechanism is validated both by experimental studies and DFT calculations.

3D printed cross-scale structured TS-1 catalysts for continuous scale-up reactions

Structured catalysts and reactors have great application prospects in gas-liquid conversion engineering due to excellent process intensification. However, the conventional fabrication process limits the designability of the hierarchical structure of monolithic catalysts, the establishment of structure-activity relationships, and slows down the speed of catalyst development. Here, we establish a structure-activity mechanism for cross-scale structures of a 3D-printed functionally gradient modular monolithic TS-1 catalyst (FGMMC) and catalytic performance by adjusting hierarchical structure distribution based on catalytic reaction simulations. The effects of uniform and gradient structures with different TS-1 contents and unit cell sizes on the catalytic properties of modular monolithic TS-1 catalyst (MMC) were investigated. In one-step scale-up reactions of ethylene to high-value-added ethylene glycol (EG), FGMMC exhibits superior catalytic efficiency than traditional powder, extrusion-dripping beads, and uniform catalysts. After a 27-h continuous scale-up catalytic test, FGMMCs exhibit excellent wear resistance (only 1.39% mass loss) and an outstanding EG yield of 82.5%. 3D-printed FGMMCs act as self-activators with a 37% reaction rate increase after rapid post-activation treatments. This work provides a low-cost and recyclable manufacturing method for achieving the functional and structural integration of catalysts and reactors by 3D printing while predicting and rapidly validating scale-up reactions.

Low-temperature ignition and oxidation mechanisms of tetrahydropyran

Cyclic ethers are relevant as next-generation biofuels and are also combustion intermediates that follow directly from unimolecular decomposition of hydroperoxyalkyl radicals. Accordingly, cyclic ether reactions are crucial to understanding low-temperature oxidation for advanced compression-ignition applications in combustion where peroxy radials are central to degenerate chain-branching pathways. Reaction mechanisms relevant to low-temperature ignition of cyclic ethers contain intrinsic complexities due to competing reactions of carbon-centered radicals formed in the initiation step undergoing either ring-opening or reactions with O2. To gain insight into mechanisms describing tetrahydropyran combustion, ignition delay time and speciation measurements were conducted. The present work integrates measurements below 1000 K of ignition delay times and species profiles in rapid compression machine experiments from 5 – 20 bar, spanning several equivalence ratios, with jet-stirred reactor experiments at 1 bar and stoichiometric conditions. The experiments are complemented with the development of the first chemical kinetics mechanism for tetrahydropyran that includes peroxy radical reactions, including O2-addition to tetrahydropyranyl (Ṙ), HOȮ-elimination from tetrahydropyranylperoxy (ROȮ) and hydroperoxytetrahydropyranyl (Q˙OOH), bi-cyclic ether formation, β-scission of Q˙OOH, and ketohydroperoxide formation.Negative-temperature coefficient (NTC) behavior is exhibited in the experiments and is reflected in the model predictions, which were within experimental uncertainty for several conditions. Disparities between the model predictions and experiments were analyzed via sensitivity analysis to identify contributing factors from elementary reactions. The analyses examine the role of ring-opening products of tetrahydropyranyl and hydroperoxytetrahydropyranyl isomers to identify reaction mechanisms that may contribute to model uncertainties. The detection of 66 species in the JSR experiments indicates that tetrahydropyran undergoes complex reaction networks, which includes interconnected reactions of aldehyde radicals and alkyl radicals. Primary radicals pentanal-5-yl and butanal-4-yl are derived from ring-opening reactions of tetrahydropyran-1-yl and undergo subsequent decarbonylation to form alkyl radicals (1-butyl and 1-propyl) that undergo reaction with O2 and may contribute to chain-branching, in addition to pathways involving tetrahydropyran-derived ketohydroperoxides.

Regulating the Thermal Behavior of Nitrocellulose by Stable Incorporation of a Green Supramolecular Salt

Commonly used inorganic potassium salts present challenges in nitrocellulose (NC)-based propellants due to poor dispersion, destabilization, and toxic byproduct formation. Environmental concerns drive interest in green flame suppressants. Here, we report a green supramolecular salt, carboxymethyl-cyclodextrin potassium (CM-CD-K) through alkalinization and etherification reaction. Molecular dynamic simulations reveal stronger interactions between CM-CD-K and NC. The loading of CM-CD-K within NC forms a stable structure with resistance to migration and defense against crystalline precipitation. Remarkably, static combustion tests show reduced flame areas and harmful gas concentrations compared to traditional potassium salt-doped NC. Kinetic analysis reveals a shift from order to Kamal-Sourour reaction with CM-CD-K addition. CD-based hybrid organic salts hold potential as eco-friendly propellant alternatives.

Electrochemistry and Organic Synthesis: New Adventures with Olefin Coupling Reactions and Electrode Surfaces

Electrochemistry has long offered opportunities to explore new modes of reactivity, new approaches for introducing selectivity into synthetic reactions, and new strategies for the synthesis of everything from complex molecules to complex, addressable molecular surfaces. In the talk to be given, two aspects of our efforts along these lines will be detailed. In the first, we will take a look at recent efforts to use anodically-generated reactive intermediates to convert readily available small molecules into functionalized synthetic building blocks and natural product derivatives. Key to these efforts are oxidation reactions that generate reactive radical cation and radical intermediates. In one application, newly available chiral lactols synthesized using methodology developed by the Lin (Cornell) and Miller (Yale) groups are being transformed into C-glycoside and aza-C-glycoside derivatives. The reactions take advantage of oxidation reactions of either enol ether or vinylsulfide groups. The cyclization reactions and the subsequent deprotection strategy needed for converting the cyclization products into a useful synthetic building block will be highlighted. In a second application of an anodic cyclization, the role of thioamides in reactions targeting the chrysosoporazine family of natural products will be discussed. The reactions seek to provide an efficient method for converting lignin derived building blocks into molecules that reduce the efflux of anticancer drugs from cells. Initial cyclization attempts utilizing amide based N-radicals and anodic olefin coupling reactions were not successful. Those reactions consistently led to over-oxidation of the products that contain a highly electron-rich aryl ring. The use of thio-amide derived radicals provides a method to circumvent this problem.In the second topic to be discussed, the question of how one might begin to induce asymmetry into such electrochemical cyclizations will be highlighted. The chemistry focuses on efforts to influence the course of both electrochemical oxidation and reduction reaction and non-redox based transition metal catalyzed reactions with the surface of an electrode.

Catalytic Enantioselective [4+2] Cycloadditions of Salicylaldehyde Acetals with Enol Ethers.

A readily accessible conjugate-base-stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde-derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2- and 4-positions. Stereochemically more complex products can be obtained from racemic enol ethers. Spirocyclic products are also accessible.

Polyepichlorohydrin grafted poly(phenylene oxide) to construct hydrophilic and hydrophobic microphase separation anion exchange membrane

An anion exchange membrane (QAPECH-g-PPO) with polyepichlorohydrin (PECH) as the main chain and poly(phenylene oxide) (PPO) as the side chain was prepared by Williamson etherification reaction. Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) characterization indicate that PECH grafted with PPO can effectively form a hydrophilic and hydrophobic phase separation structure. The amount of and molecular weight of PPO grafted has different effects on the membrane properties. As the amount of PPO grafted increases, the tensile strength of the membrane gradually increases. When the amount of PPO grafted exceeds 44%, the excessive hydrophobic phase prevents the formation of continuous ionic channels in the hydrophilic phase, leading to a significant decrease in ionic conductivity. When the amount of PPO is 38%, the ionic conductivity can reach 72 mS cm−1 (80 °C), while the swelling ratio is only 15%. Moreover, higher molecular weight PPO at 38% amount improves tensile strength of QAPECH-g-PPO membrane. The higher the molecular weight of PPO, the more stable the π - π stacking structure is formed, leading to more aggregation of hydrophobic phases in the anion exchange membrane and weakened constraints on ion clusters. Therefore, the water absorption and ion conductivity slightly increase.

Insight into the enhanced catalytic performance of phosphate-modified ZrO2/SBA-15 for the conversion of biobased 2,5-dimethylfuran and ethylene into p-xylene

Catalytic conversion of biomass-derived platform chemicals into bulk chemicals p-xylene (PX) is appealing yet challenging due to low catalytic efficiency and severe reaction conditions. In this work, we fabricated a series of phosphate-modified ZrO2/SBA-15 (xP-Zr/SBA-15) via adjusting the addition of phosphoric acid, and used them for the catalytic conversion biomass-derived 2,5-dimethylfuran (DMF) and ethylene to PX. Because of the enhanced adsorption capability for the reactant molecules (DMF and ethylene) and the good synergistic effect between Brønsted acid sites (P-OH) and Lewis acid sites (Zr4+), 30P-Zr/SBA-15 revealed an excellent catalytic performance in the selective conversion of DMF into PX. The DMF conversion was 98.5%, PX yield was 92.0% at 250 °C for 12 h, and the corresponding PX productivity was upto 50.5 mmolPX·gcat−1·h−1. The results are far superior to those obtained on most previously reported catalysts in the literature under similar reaction conditions. The kinetic study revealed that 30P-Zr/SBA-15 has a lower apparent activation energy for the tandem reaction including the Diels-Alder reaction (57.0 kJ·mo−1) and dehydration reaction (37.7 kJ·mo−1). Moreover, the 30P-Zr/SBA-15 catalyst exhibited the excellent recyclability and could be recycled at least six times without a significant loss of activity. On the basis of the temperature-programmed surface reaction of DMF and ethylene, a reasonable reaction mechanism was proposed.

First enantioselective total synthesis of human MAO inhibitor (+)-Colveol A

We present the first enantioselective total synthesis of the human MAO inhibitor (+)-colveol A and preliminary studies toward the synthesis of (+)-colveol B. Three strategies, centered on Sharpless asymmetric dihydroxylation, were explored to construct the vicinal syn-dihydroxyl system. The initial attempt involving direct asymmetric dihydroxylation of a chalcone derivative was unsuccessful. Alternatively, successful synthetic routes for (+)-colveol A involved Sharpless dihydroxylation of a cinnamyl ester, a Grignard addition of a resorcinol moiety, Wittig reaction and BBr3-mediated global deprotection of MOM ethers as key steps. The synthesis of (+)-colveol A was accomplished in 30 % yield over 7 steps.

Continuous Anhydrous Synthesis of Oxymethylene Dimethyl Ethers by Reaction of Dimethyl Ether with Molecular Formaldehyde.

A novel gaseous synthesis route to oxymethylene dimethyl ethers (OMEn, n = 3-5) starting from CO2 and green H2 by using molecular formaldehyde (FA) and dimethyl ether (DME) is presented. The anhydrous reaction runs in a pressure free, gaseous, and continuous reaction setup. Hetero-geneous cata-lysts including zeolites and ion exchange resins (IER) are investigated, if they catalyze this reaction. While IER is almost inactive, zeolites with a 3D pore structure and an acidity exceeding ρm,H+(NH3,ads) = 250 µmol·gcat.-1 proved to be catalytically active. DME conversions of up to 2.76 mol-% are observed. The observed product gas stream compositions confirm thermo-dynamic considerations with back reactions / OMEn decomposition occurring as part of the equilibria under the investigated reaction conditions (90…180 °C). However, feed gas ratio variations (FA:DME = 1:2 to 1:9.5) highlighted the possibility to shift the product selectivity in favor of OMEn and suppress FA disproportionation to methyl formate. FA trimerization to trioxane is almost completely suppressed by running the reaction at 120 °C. The results presented here provide an important and unprecedented contribution to understand the complex reaction network in the OMEn synthesis reaction necessary to establish an energy efficient sustainable OMEn production process.

Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.