Showing papers on "Ether published in 2006"

Palladium-catalyzed alkylation of sp2 and sp3 C-H bonds with methylboroxine and alkylboronic acids: two distinct C-H activation pathways.

Abstract: Palladium-catalyzed alkylations of sp2 and sp3 C−H bonds with either methylboroxine or alkylboronic acids were developed. Ag2O or AgCO3 is used as a crucial oxidant and promoter for the transmetalation step. Ether, ester, alcohol, and alkene functional groups are tolerated. A new C−H activation pathway differing from the cyclometalation process is elucidated using methylboroxine as the coupling partner.

The Selective Reaction of Aryl Halides with KOH: Synthesis of Phenols, Aromatic Ethers, and Benzofurans

Abstract: The direct and selective synthesis of phenols from aryl/heteroaryl halides and KOH has been achieved through the use of highly active monophosphine-based catalysts derived from Pd(2)dba(3) and ligands L1 or L2 and the biphasic solvent system 1,4-dioxane/H(2)O We have also demonstrated a one-pot method of phenol formation/alkylation for the preparation of alkyl aryl ethers from aryl halides In many instances, this protocol overcomes limitations in existing Pd-catalyzed coupling reactions of aliphatic alcohols with aryl halides Finally, we demonstrate that substituted benzofurans can be prepared efficiently via a Pd-catalyzed phenol formation/cyclization protocol starting from 2-chloroaryl alkynes

Selective Carbonylation of Dimethyl Ether to Methyl Acetate Catalyzed by Acidic Zeolites

Abstract: Methanol carbonylation is currently used to produce acetic acid with Rh and Ir organometallic complexes and iodide cocatalysts. Zeolites and Keggin polyoxometallate clusters also catalyze the carbonylation of alcohols and ethers (Koch reaction) to form carboxylic acids and esters. Surface alkyl groups, formed by alcohol dissociation, alkene protonation, or alkane deprotonation at acidic sites react with CO to form acylium ions, which then form carboxylic acids and esters, as in the reactions of isobutane on sulfated zirconia and tert-butyl alcohol 8] on acidic ZSM5, MOR, BEA, and Y-zeolites to form pivalic acid. Carbonylation of methanol and dimethyl ether (DME) on acidic zeolites and polyoxometallate clusters occurs concurrently with side reactions (Scheme 1) and significant catalyst deactivation. 9–13]

New biocomponents from glycerol

Abstract: Glycerol is a by-product of biodiesel production, for which new uses are being sought. Etherification of glycerol with isobutene in liquid phase with acidic ion exchange resin catalyst gave five product ethers and, as a side reaction, isobutene reacted to C8–C16 hydrocarbons. The effect of the reaction conditions on the system was studied and conditions for optimal selectivity toward ethers were discovered near with isobutene/glycerol molar ratio of 3 at 80 °C. The conditions controlling the distribution of the product ethers were studied and it was found that the extent of the etherification reaction and thus the main ether products can be changed by varying the reaction conditions.

Facile amine formation by intermolecular catalytic amidation of carbon-hydrogen bonds.

Abstract: A simple copper-based catalytic system has been developed for the carbon−hydrogen amidation reaction. The copper−homoscorpionate complex TpBr3Cu(NCMe) catalyzes the transfer of the nitrene unit NTs (Ts = p-toluenesulfonyl) and its subsequent insertion into the sp3 C−H bonds of alkyl aromatic and cyclic ethers or the sp2 C−H bonds of benzene using PhINTs as the nitrene source, affording the corresponding trisubstitued NR1HTs amines in moderate to high yields. The use of the environmentally friendly chloramine-T has also proven effective, with the advantage that sodium chloride is formed as the only byproduct. A tandem, one-pot consecutive nitrene−carbene insertion system has been developed to yield amino acid derivatives.

Pyrazolopyranopyrimidines as a class of anti-inflammatory agents.

Abstract: Pyrazolopyranopyrimidines 6a-c and 8a-c were prepared from the reaction of compounds 4a-c or 7a-c with methylamine or ammonium hydroxide solutions. Treatment of compounds 6a-c or 8a-c with 2-chloroethyl methyl ether afforded their corresponding acyclonucleosides 9a-c or 10a-c, respectively, as a new class of acyclonucleosides. All prepared compounds were tested as anti-inflammatory agents and some of them revealed moderate to potent anti-inflammatory activity.

Toward a better understanding of the lignin isolation process from wood.

Abstract: The recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) coupled with the novel combination of derivatization followed by reductive cleavage (DFRC) and quantitative 31P NMR spectroscopy were used to better understand the lignin isolation process from wood. The EMAL protocol is shown to offer access at lignin samples that are more representative of the overall lignin present in milled wood. The combination of DFRC/31P NMR provided a detailed picture on the effects of the isolation conditions on the lignin structure. More specifically, we have used vibratory and ball milling as the two methods of wood pulverization and have compared their effects on the lignin structures and molecular weights. Vibratory-milling conditions cause substantial lignin depolymerization. Lignin depolymerization occurs via the cleavage of uncondensed β-aryl ether linkages, while condensed β-aryl ethers and dibenzodioxocins were found to be resistant to such mechanical action. Condensation and side chai...

Low-Temperature Solution Route to Macroscopic Amounts of Hydrogen Terminated Silicon Nanoparticles

Abstract: A new solution route for preparing gram-scale, hydrogen terminated silicon nanoparticles is presented. Dimethoxyethane and diocytl ether have been used to prepare silicon nanoparticles via a solution reaction between sodium silicide and ammonium bromide. The reaction products are isolated as a clear yellow-orange solution and a dark black powder. Both the solution and the powder have been characterized.

Cobalt-Catalyzed Trimethylsilylmethylmagnesium-Promoted Radical Alkenylation of Alkyl Halides: A Complement to the Heck Reaction

Abstract: A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield β-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes ...

Synthesis of Indenyl Ethers by Gold(I)-Catalyzed Intramolecular Carboalkoxylation of Alkynes

Abstract: The gold(I)-catalyzed carboalkoxylation of alkynes to form indanone derivatives from readily available ortho-acetylenic benzylic ethers is described. Importantly, the gold(I)-catalyzed rearrangement of enantioenriched benzylic ethers proceeds with chirality transfer, thus providing a practical method for the enantioselective synthesis of indenyl ethers.

Intramolecularly Dinuclear Magnesium Complex Catalyzed Copolymerization of Cyclohexene Oxide with CO2 under Ambient CO2 Pressure: Kinetics and Mechanism

Abstract: The intramolecularly dinuclear magnesium complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with n-Bu2Mg followed by treatment with alcohol additive were found to be efficient catalysts for the copolymerization of CO2 and cyclohexene oxide (CHO), affording the completely alternating poly(cyclohexene carbonate) (PCHC) under extremely mild conditions (1 atm pressure of CO2, temperatures ranging from 20 to 60 °C). Ligand substituent effects were observed to dramatically influence both the activity and the chemoselectivity of the catalysis, exemplifying the fine-tunability of this type of ligands. With regard to the mechanistic studies, end-group analysis of the copolymer by MALDI-TOF mass spectroscopy revealed the predominance of the butoxy-initiated CO2/CHO copolymerization process. The butoxy-containing catalytically active species in the present system was proposed to possess a dinuclear structure similar to an isolated model Mg complex which was characterized by X-r...

Size-controlled preparation of magnetite nanoparticles in the presence of graft copolymers

Abstract: Stable aqueous iron oxide nanoparticle dispersions were prepared by coprecipitation of ferrous (Fe2+) and ferric (Fe3+) aqueous solution by a base in the presence of graft copolymers, poly(glycerol monoacrylate)-g-poly(PEG methyl ether acrylate) (PGA-g-PEG). PGA-g-PEG was prepared by acidic hydrolysis of poly(solktal acrylate)-g-poly(PEG methyl ether acrylate), which was synthesized by copolymerization of solktal acrylate and PEG methyl ether acrylate by atom transfer radical polymerization (ATRP). The size of the magnetite nanoparticles can be controlled from 4 nm to 18 nm by varying the graft density of the graft copolymers. Structural characterization using X-ray diffraction showed the presence of only the magnetite phase in the nanoparticles. Thermogravimetric analysis confirmed the presence of the graft copolymers on the magnetite surface. The magnetic characterization of the nanoparticles showed that they were superparamagnetic at room temperature.

Effect of γ-alumina content on catalytic performance of modified ZSM-5 for dehydration of crude methanol to dimethyl ether

Abstract: The effect of γ-alumina as a binder on the catalytic performance of Na-modified ZSM-5 was investigated by using the dehydration of methanol to dimethyl ether (DME). A series of modified ZSM-5 catalysts were prepared with/without γ-alumina and the activity of each catalyst was examined in the dehydration of crude methanol to DME using a fixed-bed reactor at the reaction pressure of 10 atm and LHSV of 10 h −1 . The surface and pore characteristics were investigated by Ar adsorption and the acid properties were studied by TPD of ammonia and FT-IR of adsorbed pyridine. Though the addition of γ-alumina lowered the activity of NaHZSM-5, it broadened the operative temperature range (OTR), thereby resulting in more stable catalysts. The ZSM-5 containing 70% of γ-alumina was found to be an efficient catalyst, exhibiting quite high activity as well as wide OTR. This beneficial effect is ascribed to the adequate dilution of the strong acid sites of ZSM-5 in the γ-alumina matrix.

Mix-and-Heat Benzylation of Alcohols Using a Bench-Stable Pyridinium Salt

Abstract: 2-Benzyloxy-1-methylpyridinium triflate (1) is a stable, neutral organic salt that converts alcohols into benzyl ethers upon warming. The synthesis and reactivity of 1 are described herein. Benzylation of a wide range of alcohols occurs in good to excellent yield.

Enzyme‐catalyzed regioselective synthesis of sugar esters and related compounds

Abstract: In this review, a comprehensive and illustrative survey is made of the regioselective synthesis of esters of sugars and related compounds using lipases. The main emphasis has been given to the screening and use of commercially available lipases for the enzymatic esterification of neutral monosaccharides, disaccharides, sugar alcohols and their selected ether and ester derivatives. The effect of solvents and solubilizing agents in improving the yields of the resultant sugar fatty acid esters has been incorporated. Further, solvent-free esterification with molten fatty acids, use of ionic liquids and microwave radiations for improvement in the methodology have also been discussed. Copyright © 2006 Society of Chemical Industry

Solid-State NMR Study of Two Classic Proton Conducting Polymers: Nafion and Sulfonated Poly(ether ether ketone)s

Abstract: Proton mobilities in Nafion and sulfonated poly(ether ether ketone) (S-PEEK) have been studied using high-resolution solid-state 1H NMR under fast magic angle spinning (MAS). These studies demonstrated proton exchange between sulfonic acid groups and water within both Nafion and S-PEEK. Variable temperature experiments were used to determine the activation energy for proton transport in pure Nafion, found to be 11.0 kJ/mol, which is lower than those determined for S-PEEKs with different degrees of sulfonation. Increasing proton exchange rates with increasing temperature indicate the expected dependence of proton mobility on temperature. A rotor-synchronized homonuclear double quantum filter sequence (BaBa) was used to disclose the nature of the H-bonding interactions in the two polymers, from which a model of the proton interactions in the polymers is developed.

Quantitative synthesis of star-shaped poly(vinyl ether)s with a narrow molecular weight distribution by living cationic polymerization.

Abstract: Star-shaped poly(vinyl ether)s with narrow molecular weight distributions were obtained from polymer-linking reactions of living polymers with a divinyl compound based on living cationic polymerization. For example, living polymers (DPn = 50−300) of isobutyl vinyl ether (IBVE), prepared with a cationogen/EtAlCl2 at 0 °C in hexane in the presence of ethyl acetate, were allowed to react with a small amount of 1,4-cyclohexanedimethanol divinyl ether (DVE-1) to give a star-shaped poly(IBVE) in quantitative yield (100%). In addition, a notable feature of this star-shaped polymer was extremely narrow molecular weight distribution (Mw/Mn = 1.1−1.2). The structure of divinyl compounds and reaction conditions for the linking reaction are key factors for achieving quantitative yield of star-shaped polymers. To our best knowledge, this is the first example of selective preparation of star-shaped polymers with narrow molecular weight distribution via one-pot polymer-linking reactions, which has never been achieved in...

Preparation of polytrimethylene ether glycol and copolymers thereof

Abstract: The present invention relates to a process comprising using ionic liquids for the polycondensation of 1,3-propanediol reactants to produce polytrimethylene ether glycol and copolymers thereof.

Gold Catalysis: Phenol Synthesis in the Presence of Functional Groups

Abstract: The effect of different substituents, such as bromo, chloromethyl, hydroxymethyl, formyl, acetyl, carboxy, and acylated hydroxymethyl and ammonium groups, on the furan ring of substrates in gold-catalyzed phenol synthesis has been investigated. The furan ring was also replaced by different heterocycles, such as pyrroles, thiophenes, oxazoles, and a 2,4-dimethoxyphenyl group; gold catalysis then delivered no phenols, but occasionally other products were obtained. [Ru(3)(CO)(12)] also catalyzed the conversion of 1 at a low rate, [Os(3)(CO)(12)] failed as a catalyst, and with [Co(2)(CO)(8)] the alkyne complex 19 can be obtained, it does not lead to any phenol but reacts with norbornene to give the product of a Pauson-Khand reaction. Efforts to prepare vinylidene complexes of 1 provided the only evidence for these species; in the presence of a phosphane ligand with ruthenium an interesting deoxygenation to 22 was observed. The phenol 2 c was converted to the allyl ether, a building block for para-Claisen rearrangements, and to the aryl triflate, a building block for cross-coupling reactions.