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Results 501 - 550 of 2316
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Biaggi Cinzia - - 2010
Starting from (R)-6,6'-dimethyldiphenyl-2,2'-dicarboxylic acid, a novel class of enantiomerically pure cyclic dialkyl phosphates was synthesized and properly characterized. The absolute configuration was determined by 2D NOESY experiments. The catalytic behavior of the new chiral Bronsted acids was investigated in the stereoselective addition of a silyl keteneacetal to aldimines. The Mannich-type ...
Artok Levent - - 2010
Unsymmetric diynes possessing a terminal alkyne moiety reacted with organoboronic acids both chemo- and stereoselectively to afford arylated or alkenylated exocyclic dienes by catalysis from the [Rh(cod)OCH(3)](2) complex. The use of a polar protic solvent, e.g. CH(3)OH is required for the success of the process under mild conditions.
Shuai Danmeng - - 2010
Azo dyes are widespread pollutants and potential cocontaminants for nitrate; we evaluated their effect on catalytic reduction of a suite of oxyanions, diatrizoate, and N-nitrosodimethylamine (NDMA). The azo dye methyl orange significantly enhanced (less than or equal to a factor of 5.24) the catalytic reduction kinetics of nitrate, nitrite, bromate, ...
Kalita Pranjal - - 2010
Here we demonstrate for the first time the preparation of a triflic acid (TFA)-functionalized mesoporous nanocage with tunable pore diameters by the wet impregnation method. The obtained materials have been unambiguously characterized by XRD, N(2) adsorption, FTIR spectroscopy, and NH(3) temperature-programmed desorption (TPD). From the characterization results, it has been ...
Chen Bing - - 2010
A new chemo-enzymatic route to both isomers of 2-hydroxy-4-phenylbutyric acid is reported. The key step is the lactonase-catalyzed hydrolysis of cis- and trans-2-hydroxy-4-phenyl-4-butyrolactones followed by hydrogenation over Pd/C to afford optically pure 2-hydroxy-4-phenylbutyric acid.
Christiansen Elisabeth - - 2010
A protocol for rapid and efficient Pd/Cu-catalyzed coupling of aryl bromides and iodides to terminal alkynes has been developed with use of 2-(di-tert-butylphosphino)-N-phenylindole (cataCXium PIntB) as ligand in TMEDA and water. The new protocol successfully couples substrates which failed with standard Sonogashira conditions, and enables an efficient general synthetic route ...
Yang Xing X Department of Chemistry, Washington University, Campus Box 1134, One Brookings Drive, St. Louis, Missouri 63130, - - 2010
Enantioselective acyl transfer catalyst benzotetramisole (BTM) has been found to promote dynamic kinetic resolution of azlactones providing di(1-naphthyl)methyl esters of alpha-amino acids with up to 96% ee.
Niralwad Kirti S - - 2010
1-Hexanesulphonic acid sodium salt was found to be an efficient catalyst for the green synthesis of alpha-aminophosphonates by the coupling of aldehydes/ketone, an amine and triethyl phosphite under ultrasound irradiation at ambient temperature for appropriate time to furnish the desired product in good to excellent yield under solvent-free condition. This ...
Deng Weiping - - 2010
Cellulose can be transformed into methyl glucosides in methanol with yields of 50-60% in the presence of several acid catalysts under mild conditions (< or = 473 K); H(3)PW(12)O(40) provides the highest turnover number (approximately 73 in 0.5 h) for the formation of methyl glucosides among many acid catalysts examined.
Bi Hai-Peng - - 2010
An interesting aldehyde- and ketone-induced intermolecular tandem decarboxylation-coupling (Csp(3)-Csp) catalyzed by copper with use of natural alpha-amino acids as starting materials is developed under neutral conditions with the production of CO(2) and H(2)O as the only byproducts. Various functionalized nitrogen-containing compounds were obtained by this method. In these processes, interesting ...
Avenoza Alberto - - 2010
The synthesis and conformational analysis of a new type of conformationally restricted alpha-amino acid analogue of the amino acid antibiotic furanomycin is presented. The restriction involves the cis-fused cyclobutane and tetrahydrofuran units, generating the unusual 2-oxabicyclo[3.2.0]heptane core, which is found in a great number of biologically active natural products. The ...
Coulbeck Elliot - - 2010
The parallel kinetic resolution of racemic 2-aryl-2-deuterio-propionic and butanoic acids using an equimolar combination of quasi-enantiomeric oxazolidin-2-ones is discussed. The levels of diastereoselectivity were high leading to enantiomerically pure D-labeled products in good yield.
Rafiee Ezzat - - 2011
A series of 12-phosphotungstic acid (PWA) supported on various porous carriers, such as silica, alumina, titania, clay, and carbon were prepared, and their catalytic performance evaluated in the synthesis of imidazoles in solvent-free condition. It was found that PWA supported on silica (PWA/SiO(2)) showed higher activity compared to other catalysts. ...
Wilson Zoe E - - 2010
The one-pot Horner-Wadsworth-Emmons/oxa-Michael cascade followed by spiroketalisation affords the tetracyclic benzannulated spiroketal core of berkelic acid, an extremophile natural product with selective activity against ovarian cancer.
Gong Shuwen - - 2010
A mild and clean liquid nitration of benzene with 65% nitric acid as nitrating agent over silica supported ammonium salt of 12-molybdophosphoric acid catalysts has been investigated. These catalysts with different loadings were prepared by sol-gel method and characterized by X-ray diffraction (XRD) and FTIR spectra. The acidity of these ...
Kurouchi Hiroaki - - 2010
The chemical features, such as substrate stability, product distribution, and substrate generality, and the reaction mechanism of Br?nsted superacid-catalyzed cyclization reactions of aromatic ring-containing acetoacetates (beta-ketoesters) were examined in detail. While two types of carbonyl cyclization are possible, i.e., keto cyclization and ester cyclization, the former was found to take ...
Cui Sheng - - 2010
The enantioselective conjugate addition of alkynyl nucleophiles has been a long-standing challenge in synthetic chemistry. This paper describes a highly practical asymmetric conjugate alkynylation of Meldrum's acid-derived acceptors using cinchonidine (<$100/kg) as the chiral mediator. The process provides practical access to chiral beta-alkynyl acids. Noteworthy attributes of the method are ...
Shi Bing-Feng - - 2010
Pd(II)-catalyzed enantioselective C-H olefination of diphenylacetic acid substrates has been achieved through the use of monoprotected chiral amino acid ligands. The absolute configuration of the resulting olefinated products is consistent with that of a proposed C-H insertion intermediate.
Grajciar L - - 2010
Periodic DFT calculations were performed on H-FER models having Si/Al ratios of 71 : 1, 35 : 1 and 8 : 1, in order to investigate the effect of aluminium content on the properties of the zeolite Br?nsted acid sites. Relative stability of these sites was found to be dependent ...
Atkins Martin P - - 2010
Selected Br?nsted acidic ionic liquids were tested as homogeneous catalysts for the dehydration of methanol to dimethyl ether. Ionic liquids incorporating an alkanesulfonic acid as a part of the cation, a complex acidic anion, [A(2)H](-), or both, proved to be good catalysts for this process, providing high conversions and selectivities. ...
Liu Jiehua - - 2010
We have successfully designed and synthesized core-shell multicomponent TiP nanospheres with a stable crystal core and orderly open nanopores, which have uniform distribution and good dispersion and offer great potential as a highly active Br?nsted acid catalyst.
Xu Kuo-Xi - - 2011
Four novel derivatives of BINOL bearing S-tryptophan unit have been prepared and the structures of these compounds characterized by IR, MS, (1)H and (13)C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and (1)H NMR spectroscopy. The receptors exhibited different chiral ...
Marcoux David - - 2010
We describe our studies on the effect of various Lewis bases and Br?nsted acids as achiral additives on the stereoselectivity of some Rh(ii)-catalyzed cyclopropanations.
Shiina Isamu - - 2010
A variety of optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates are produced by the kinetic resolution of racemic 2-hydroxyalkanoates by using achiral 2,2-diarylacetic acid with hindered carboxylic anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic anhydride, and (+)-(R)-benzotetramisole ((R)-BTM) effectively produces (S)-2-hydroxyalkanoates and (R)-2-acyloxyalkanoates from the ...
Sun Chang-Liang - - 2010
Useful methods have been developed to construct ortho-arylated aryl aldoximes, aryl ketoximes, and fluorenones via Pd(II)-catalyzed direct C-H arylation by using arylboronic acids as arylating reagents based on the analysis of the pathways of direct functionalization of aryl aldoximes.
Zamfir Alexandru - - 2010
A first organocatalytic enantioselective route was developed for the conversion of readily prepared and air stable aliphatic hydrazones to synthetically valuable alpha-hydrazinonitriles. This BINOL-phosphate catalyzed Strecker-type reaction (see scheme, Ar = p-NO(2)-Ph) provides a new practical and direct route to alpha-hydrazino acids of synthetic and biological importance. The actually active ...
Cheng Po-Wen - - 2010
The title compound, C(8)H(6)O(6)·2H(2)O, was obtained by accident within a project on the synthesis of metal-organic coordination polymers by the reaction of LiOH with 2,5-dihy-droxy-terephthalic acid under solvothermal conditions. The asymmetric unit consists of half a 2,5-dihy-droxy-terephthalic acid mol-ecule located on a centre of inversion and one solvent water mol-ecule ...
Rochais Christophe - - 2010
β-Aryl-β-amino acids constitute very useful scaffolds able to lead, via various intra-molecular cyclisation reactions, to a great diversity of cyclic derivatives with numerous biological and therapeutic properties. The present article aims at reporting an exhaustive overview of these ring-closure sequences and their application in the medicinal chemistry field.
Liu Xiao-Yan - - 2010
Sulfonated (SO(3)H-bearing) activated carbon (AC-SO(3)H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO(3)H density of 0.64 mmol·g-1 and a specific surface area of 602 m2·g-1. The catalytic properties of AC-SO(3)H were compared with that of two commercial solid acid catalysts, Nafion NR50 and ...
Nitsch-Velasquez Lucia - - 2010
The optical rotation of natural amino acids becomes more positive when the medium is changed from approximately neutral to strongly acidic (Clough-Lutz-Jirgensons (CLJ) effect). In this work, it is shown by time-dependent density functional computations that the effect can be generalized to other α-substituted chiral carboxylic acids. The physical origin ...
Mphahlele Malose Jack - - 2010
Palladium-catalyzed Suzuki cross-coupling of 2-aryl-4-chloro-3-iodoquinolines with excess arylboronic acids (2.5 equiv.) in the presence of tricyclohexylphosphine afforded the 2,3,4-triarylquinolines in one-pot operation. The incipient 2,3-diaryl-4-chloroquinolines were also prepared and transformed to the primary 4-amino-2,3-diarylquinolines and 2,3-diarylquinolin-4(1H)-ones.
Wang Jiang - - 2010
Alpha,beta-Diamino acids have attracted considerable attention recently due to their growing importance in pharmaceutical and biochemical research. For example, this special class of alpha,beta-diamino acids has become the components of enzyme inhibitors, and has been incorporated into peptides which are used to modulate secondary and tertiary structural conformations. Although their ...
Samek Ota - - 2010
Algae are becoming a strategic source of fuels, food, feedstocks, and biologically active compounds. This potential has stimulated the development of innovative analytical methods focused on these microorganisms. Algal lipids are among the most promising potential products for fuels as well as for nutrition. The crucial parameter characterizing the algal ...
Murugan Kaliyappan - - 2010
A mild, selective and efficient Nazarov cyclization of divinyl ketones catalyzed by phosphomolybdic acid (PMA) is described. The process demonstrates a broad substrate scope with functional group tolerance under short reaction times. PMA supported on silica gel is more efficient than the bulk catalyst and is recycled up to three ...
Thiverny Maryse - - 2010
The resolution of chiral nitrones via derivatization of hydroxylamines was applied to MiPNO, a new, stable, easily prepared chiral cyclic nitrone. The application of MiPNO in totally regio- and diastereo-selective 1,3-dipolar cycloaddition reactions provides an expeditious enantioselective access to unusual gamma-hydroxy alpha-amino acids.
Choi Yoon Kyung - - 2009
The complete conversion of racemic amino acid amides to optically active amino acid derivatives was accomplished via lipase/palladium-catalyzed dynamic kinetic resolution (DKR). In the DKR, a lipase catalyzes the selective acylation of L-substrate in the presence of acyl donor while unreacted D-substrate is isomerized by a Pd nanocatalyst to L-substrate. ...
De Nisco Mauro - - 2009
Dipeptides obtained from l-proline and beta(3)-l-amino acids are reported to catalyze enantioselective direct aldol reaction in aqueous medium, leading to significant anti:syn diastereomeric ratios and enantiomeric excesses. The simple introduction of a polar substituent at the C-2 position of the beta(3)-l-amino acid was also found to enhance appreciably both diastereo- ...
Huh Jung Oh - - 2010
The introduction of an o-carborane cage into the triarylborane significantly enhances the Lewis acidity of the boron atom leading to large increase in fluoride ion affinity.
Marsili Laura - - 2010
Lewis acid promoted elimination of p-toluenesulfinc acid from sulfonyl indazoles and sulfonyl indoles generates the corresponding iminium ion that reacts with allyltin reagents, silyl enol ethers, silyl ketene acetals and electron-rich aromatics leading to functionalized indazole and indole derivatives.
Ni Yike - - 2009
A unified approach to the pyrrolidine triacid natural products isodomoic acids G and H has been developed. Total syntheses of both natural products were completed, and determination of the correct stereostructure of isodomoic acid G was established by comparing 5'-(R) and 5'-(S) isomers to a sample of authentic material. A ...
Wada Yasufumi - - 2010
Thiosilane and a catalytic amount of a Br?nsted acid mediate the novel domino-type rearrangement reaction of the 4,4-disubstituted cyclohexadienones to produce the 3,4-disubstituted benzenethioethers; the key step is 1,2-addition of thiosilane to dienone.
Andaloussi Mounir - - 2009
The first Pd(II)-catalyzed P arylation has been performed by using palladium acetate, the rigid bidentate ligand dmphen (dmphen=2,9-dimethyl-1,10-phenanthroline), and without the addition of base or acid. Couplings of arylboronic acids or aryl trifluoroborates with H-phosphonate dialkyl esters were conducted in 30 min with controlled microwave (MW) heating under non-inert conditions. ...
Reichvilser Moritz M - - 2010
The four aldopentoses ribose, arabinose, xylose, and lyxose were evaluated to test their suitability as linear linkers for the formation of intrinsically chiral covalent organic boronic ester networks. Based on X-ray crystal structures of the reaction products with phenylboronic acid, arabinose and xylose formed boronic acid diesters. Lyxose and ribose ...
Prieto Mònica - - 2009
Alpha-amino acid derivatives, particularly those of phenylglycine, can suffer significant racemization in Suzuki couplings. When arylpinacolboronate esters are used as coupling partners this unwanted side reaction can be suppressed by the use of Pd(OAc)(2) as Pd(0) source, in the presence of Buchwald's SPhos ligand. The syntheses of biaryl amino acids ...
Zhou Lei L Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, - - 2009
Lewis acids catalyze the cyclization of methyl phenyldiazoacetates with an ortho-imino group, prepared from o-aminophenylacetic acid, to give 2,3-substituted indoles in quantitative yields.
Lee Doris - - 2009
Interactions between pyruvic acids and diphenylborinic acid form the basis of an efficient, direct, boron-catalyzed aldol reaction that takes place in water at room temperature with low catalyst loadings. Both boronic and borinic acids function as catalysts, with the latter demonstrating particularly high activity. A wide range of aldehydes, including ...
Yoshikawa Takashi - - 2009
A highly torquoselective olefination of alkynoates to provide functionalized tetrasubstituted olefins, (E)-2-en-4-ynoic acids, is described. Addition of Br??nsted acids dramatically switched the mode of the Ag(I)-catalyzed cyclization of the resulting enyne carboxylic acids to give either tetronic acids or 2-pyrones.
Cornella Josep - - 2009
A palladium catalyzed C-H activation of indoles and a silver catalyzed decarboxylative C-C activation of ortho substituted benzoic acids are synergistically combined to synthesize indoles arylated exclusively in the C-3 position. This novel decarboxylative C-H arylation methodology is compatible with electron-donating and -withdrawing substituents in both coupling partners.
Sibi Mukund P - - 2009
Lewis acid complexation is generally required for chiral-auxiliary-controlled stereoselectivity, and chiral Lewis acid catalysis is frequently optimal for introducing asymmetry. In this work, we show that nitrile ylide cycloadditions to electron-poor acceptors attached to chiral auxiliaries proceed in high yield and stereoselectivity in the absence of Lewis acids. In contrast, ...
Pahadi Nirmal K - - 2009
This manuscript details the development of a palladium-catalyzed hydroamination of vinyl ethers. It is proposed that palladium catalyzes the hydroamination via Bronsted base catalysis, where palladium is protonated by the relatively acidic sulfonamide to generate a palladium hydride as well as the active anionic sulfonamide nucleophile. Thus, this process is ...
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