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Corresponding Ester (corresponding + ester)
Selected AbstractsA Versatile Solvent-Free "One-Pot" Route to Polymer Nanocomposites and the in situ Formation of Calcium Phosphate/Layered Silicate Hybrid NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Hans Weickmann Abstract Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyurethane (PU) nanocomposites containing well-dispersed calcium phosphate/layered silicate hybrid nanoparticles were prepared in a versatile solvent-free "one-pot" process without requiring separate steps, such as organophilic modification, purification, drying, dispersing, and compounding, typical for many conventional organoclay nanocomposites. In this "one-pot" process, alkyl ammonium phosphates were added as swelling agents to a suspension of calcium/layered silicate in styrene, methyl methacrylate, or polyols prior to polymerization. Alkyl ammonium phosphates were prepared in situ by reacting phosphoric acid with an equivalent amount of alkyl amines such as stearyl amine (SA) or the corresponding ester- and methacrylate-functionalized tertiary alkyl amines, obtained via Michael Addition of SA with methyl acrylate or ethylene 2-methacryloxyethyl acrylate. Upon contact with the calcium bentonite suspension, the cation exchange of Ca2+ in the silicate interlayers for alkyl ammonium cations rendered the bentonite organophilic and enabled effective swelling in the monomer accompanied by intercalation and in situ precipitation of calcium phosphates. According to energy dispersive X-ray analysis, the calcium phosphate precipitated exclusively onto the surfaces of the bentonite nanoplatelets, thus forming easy-to-disperse calcium phosphate/layered silicate hybrid nanoparticles. Incorporation of 5,15,wt% of such hybrid nanoparticles into PMMA, PS, and PU afforded improved stiffness/toughness balances of the polymer nanocomposites. Functionalized alkyl ammonium phosphate addition enabled polymer attachment to the nanoparticle surfaces. Transmission electron microscopy (TEM) analyses of PU and PU-foam nanocomposites, prepared by dispersing hybrid nanoparticles in the polyols prior to isocyanate cure, revealed the formation of fully exfoliated hybrid nanoparticles. [source] Synthesis and some reactions of 4-(ethoxycarbonyl)-1,5-diphenyl-1H -pyrazole-3-carboxylic acidJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2007Ahmet, ener 1,5-Diphenyl-1H -pyrazole-3,4-dicarboxylic acid-4-ethyl ester 2, obtained from the 4-ethoxycarbonyl-5-phenyl-2,3-furandione 1 and N -benzylidene- N,-phenyl hydrazine, was converted via reactions of its acid chloride 3 with various alcohols or N-nucleophiles into the corresponding ester 5 or amide derivatives 6, respectively. In addition, 2 was decarboxylated to give ethyl 1,5-diphenylpyrazole-4-carboxylate 4. Nitrile 7 derivative of 2 was also obtained by dehydration of 6a in a mixture of SOCl2 and DMF. While cyclocondensation reaction of 2 with hydrazine hydrate leads to the formation of pyrazolo[3,4- d]pyridazine-4,7-dione 8, the reaction of 3 with anhydrous hydrazine provided a new bis pyrazole derivative 9. [source] Studies on the reactions of cyclic oxalyl compounds with hydrazines or hydrazones : Synthesis and reactions of 4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H -pyrazole-3-carboxylic acidJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2002Ahmet, ener The 1H -pyrazole-3-carboxylic acid 2, obtained from the furan-2,3-dione 1 and N -Benzylidene- N'-(3-nitrophenyl) hydrazine, was converted via reactions of its acid chloride 3 with various alcohols or N-nucleo-philes into the corresponding ester or amide derivatives 4 or 5, respectively. Nitrile 6 and anilino-pyrazole acid 7 derivatives of 2 were also obtained by dehydration of 5a in a mixture of SOCl2 with DMF and reduction of 2 with sodium polysulphide, respectively. While cyclocondensation reactions of 2 or 7 with phenyl hydrazine or hydrazine hydrate and 6 with only anhydrous hydrazine lead to derivatives of pyrazolo[3,4- d]-pyridazinone 8 and pyrazolo[3,4- d]pyridazine amine 9, respectivel. The reaction of 2 with 2-hydrazinopyri-dine provided hydrazono-pyrazole acid derivative 10, which was decarboxylated to give hydrazono-pyra-zole derivative 11. Pyrazolo[4,3- d]oxazinone 12 and 2-quinolyl pyrazolo[3,4- d]pyridazine 13 derivatives were also prepared by cyclocondensation reactions of 2 with hydroxylamine hydrochloride and 7 with acetaldehyde, respectively. [source] Asymmetric 1,4-Addition of Oxazolones to Nitroalkenes by Bifunctional Cinchona Alkaloid Thiourea Organocatalysts: Synthesis of ,,,-Disubstituted ,-Amino AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008José Alemán Dr. Abstract An easy and simple synthetic approach to optically active ,,,-quaternary ,-amino acids using asymmetric organocatalysis is presented. The addition of oxazolones to nitroalkenes catalyzed by thiourea cinchona derivatives provides the corresponding ,,,-quaternary ,-amino acid derivatives with good yields, excellent diastereoselectivities (up to 98,% dr), and from moderate to good enantioselectivities (up to 92,% ee). The reaction can be performed on a large scale. The optically active oxazolone,nitroalkene addition products can be opened in a one-pot reaction to the corresponding ester,amide derivatives. Additional transformations are also presented, such as the synthesis of amino esters, amino acids, and transformation into 3,4-disubstituted pyrrolidin-2-ones. [source] On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels,Alder ReactionsCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2009Michael Abstract Intramolecular Diels,Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6-31+G(d) and CBS-QB3 levels of theory for a series of 1,3,8-nonatrienes, H2CCHCHCHCH2XZCHCH2 [XZ=CH2CH2 (1); OC(O) (2); CH2C(O) (3); OCH2 (4); NHC(O) (5); SC(O) (6); OC(S) (7); NHC(S) (8); SC(S) (9)]. For each system studied (1,9), cis - and trans -TS isomers, corresponding, respectively, to endo - and exo -positioning of the CXZ tether with respect to the diene, have been located and their relative energies (ErelTS) employed to predict the cis/trans IMDA product ratio. Although the ErelTS values are modest (typically <3,kJ,mol,1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (XO,NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis -TS, namely (1),unfavorable torsional (eclipsing) strain about the C4C5 bond, that is caused by the CXC(Y) group's strong tendency to maintain local planarity; and (2),attractive electrostatic and secondary orbital interactions between the endo -(thio)carbonyl group, CY, and the diene. The former interaction predominates when X is weakly electronegative (XN, S), while the latter is dominant when X is more strongly electronegative (XO), or a methylene group (XCH2) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1, 2, 3, and 4 (published work) and 5, 6, and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans -selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14, which undergoes a more trans -selective IMDA reaction than the corresponding ester tethered precursor 13. [source] Lanthanide Formamidinates as Improved Catalysts for the Tishchenko ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2008Agustino Zuyls Abstract The tris(formamidinato)lanthanum(III) complexes [La(o -TolForm)3(thf)2] [1; o -TolForm = N,N, -bis(o -tolyl)formamidinate], [La(XylForm)3(thf)] [2; XylForm = N,N, -bis(2,6-dimethylphenyl)formamidinate], and [La(EtForm)3] [3, EtForm = N,N, -bis(2,6-diethylphenyl)formamidinate] are a new class of precatalysts for the Tishchenko reaction. Their catalytic activity is a result of their high Lewis acidity and the ease with which the ligand spheres can be interchanged. For the dimerization of benzaldehyde to give benzyl benzoate, which is a benchmark reaction, compound 1 is, to the best of our knowledge, the most active catalyst ever reported. On a preparative scale, the reaction can be performed in the absence of solvent. A range of aromatic, heteroaromatic, and aliphatic aldehydes was rapidly converted into the corresponding esters by using catalysts 1,3.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] General Method for the 11C-Labeling of 2-Arylpropionic Acids and Their Esters: Construction of a PET Tracer Library for a Study of Biological Events Involved in COXs ExpressionCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Misato Takashima-Hirano Abstract Cyclooxygenase (COX) is a critical enzyme in prostaglandin biosynthesis that modulates a wide range of biological functions, such as pain, fever, and so on. To perform in vivo COX imaging by positron emission tomography (PET), we developed a method to incorporate 11C radionuclide into various 2-arylpropionic acids that have a common methylated structure, particularly among nonsteroidal anti-inflammatory drugs (NSAIDs). Thus, we developed a novel 11C-radiolabeling methodology based on rapid C -[11C]methylation by the reaction of [11C]CH3I with enolate intermediates generated from the corresponding esters under basic conditions. One-pot hydrolysis of the above [11C]methylation products also allows the synthesis of desired 11C-incorporated acids. We demonstrated the utility of this method in the syntheses of six PET tracers, [11C]Ibuprofen, [11C]Naproxen, [11C]Flurbiprofen, [11C]Fenoprofen, [11C]Ketoprofen, and [11C]Loxoprofen. Notably, we found that their methyl esters were particularly useful as proradiotracers for a study of neuroinflammation. The microPET studies of rats with lipopolysaccharide (LPS)-induced brain inflammation clearly showed that the radioactivity of PET tracers accumulated in the inflamed region. Among these PET tracers, the specificity of [11C]Ketoprofen methyl ester was demonstrated by a blocking study. Metabolite analysis in the rat brain revealed that the methyl esters were initially taken up in the brain and then underwent hydrolysis to form pharmacologically active forms of the corresponding acids. Thus, we succeeded in general 11C-labeling of 2-arylpropionic acids and their methyl esters as PET tracers of NSAIDs to construct a potentially useful PET tracer library for in vivo imaging of inflammation involved in COXs expression. [source] | |||||||||||||||||||