- Half-sandwich ruthenium-based versatile catalyst for both alcohol oxidation and catalytic hydrogenation of carbonyl compounds in aqueous media
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A series of half-sandwich ruthenium-based catalysts for both alcohol oxidation and carbonyl compounds hydrogenation have been synthesized through metal-induced C–H bond activation based on benzothiazole ligands. The neutral ruthenium complexes 1–4 were fully characterized by UV–vis, NMR, IR, and elemental analysis. Molecular structures of complexes 1 and 3 were further confirmed by X-ray diffraction analysis. All complexes exhibited high activity for the catalytic oxidation of a variety of alcohols with tBuOOH as oxidants to give carbonyl compounds with high yields in water. Moreover, these half-sandwich complexes also showed high efficiency for the catalytic hydrogenation of carbonyl compounds in a methanol–water mixture. The catalyst could be reused for at least five cycles without any loss of activity. The catalytic system also worked well for various kinds of substrates with either electron-donating or electron-withdrawing groups.
- Qiao, Xin-Chao,Qiu, Dan-Chen,Lin, Nan,Zhu, Jing-Wei,Deng, Wei,Yao, Zi-Jian
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- Optimization of inhibitors of the tyrosine kinase EphB4. 2. Cellular potency improvement and binding mode validation by X-ray crystallography
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Inhibition of the tyrosine kinase erythropoietin-producing human hepatocellular carcinoma receptor B4 (EphB4) is an effective strategy for the treatment of solid tumors. We have previously reported a low nanomolar ATP-competitive inhibitor of EphB4 discovered in silico by fragment-based high-throughput docking combined with explicit solvent molecular dynamics simulations. Here we present a second generation of EphB4 inhibitors that show high inhibitory potency in both enzymatic and cell-based assays while preserving the appealing selectivity profile exhibited by the parent compound. In addition, respectable levels of antiproliferative activity for these compounds have been obtained. Finally, the binding mode predicted by docking and molecular dynamics simulations is validated by solving the crystal structures of three members of this chemical class in complex with the EphA3 tyrosine kinase whose ATP-binding site is essentially identical to that of EphB4.
- Lafleur, Karine,Dong, Jing,Huang, Danzhi,Caflisch, Amedeo,Nevado, Cristina
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- Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultrasound irradiation
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The solvent-free indium-promoted reaction of alkanoyl chlorides with sterically and electronically diverse arylstannanes is a simple and direct method for the regioselective synthesis of primary, secondary and tertiary alkyl aryl ketones in good to excellent isolated yields (42-84%) under mild and neutral conditions. The protocol is also adequate for the synthesis of aryl vinyl ketones. Reaction times are drastically reduced (from 3-32 h to 10-70 min) under ultrasonic irradiation. Evidences for the involvement of a homolytic aromatic ipso-substitution mechanism, in which indium metal acts as radical initiator, are presented. It is possible the transference of two aryl groups from tin, thus improving effective mass yield, working with diarylstannanes as starting substrates.
- Lo Fiego, Marcos J.,Badajoz, Mercedes A.,Domini, Claudia,Chopa, Alicia B.,Lockhart, María T.
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p. 826 - 832
(2013/03/14)
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- Electrochemically promoted Friedel-Crafts acylation of aromatic compounds
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Friedel-Crafts acylation is carried out with several aromatic substrates in the presence of an electrochemically active aluminium anode to minimize the inorganic reagents. Only a catalytic amount of AlCl3 (5 mol %) is required to enable the anodic polarization of the aluminium electrode to promote continuous acylation. This process typically gave products in good yields (70-96%).
- Karthik,Kulangiappar,Marken, Frank,Kulandainathan, M. Anbu
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p. 2625 - 2627
(2008/09/18)
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- Novel anti-Markovnikov regioselectivity in the Wacker reaction of styrenes
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The Wacker reaction is one of the longest known palladium-catalysed organic transformations, and in the vast majority of cases proceeds with Markovnikov regioselectivity. Palladium(II)-mediated oxidation of styrenes was examined and in the absence of reoxidants was found to proceed in an anti-Markovnikov sense, giving aldehydes. Studies on the mechanism of this unusual transformation were carried out, and indicate the possible involvement of a η4-palladium-styrene complex. With a heteropolyacid as the terminal oxidant, oxidation of styrene to give the anti-Markovnikov aldehyde as the major product was found to be catalytic.
- Wright, Joseph A.,Gaunt, Matthew J.,Spencer, Jonathan B.
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p. 949 - 955
(2007/10/03)
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- Acetylation of aromatic compounds over H-BEA zeolite: The influence of the substituents on the reactivity and on the catalyst stability
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The acylation with acetic anhydride of six aromatic substrates with different features (degree of activation of the aromatic ring towards electrophilic substitution, number of rings, i.e., 1 or 2) was carried out in a batch reactor at 373 K over a H-BEA zeolite (Si/Al = 15) with nitrobenzene as a solvent. The acetylation rate was found to be very dependent on the degree of ring activation, with diffusion limitations playing only a limited role. The decrease of the rate with reaction time, which was very pronounced with poorly activated and deactivated substrates, is mainly due to the inhibiting effect of acetic acid and of the products of acetic anhydride condensation.
- Guidotti, Matteo,Canaff, Christine,Coustard, Jean-Marie,Magnoux, Patrick,Guisnet, Michel
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p. 375 - 383
(2007/10/03)
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- The synthesis of arylketones via Friedel-Crafts acyldegermylation
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Electron-rich and electron-neutral aryl trialkylgermanes are shown to be competent precursors to aryl ketones via Friedel-Crafts acyldegermylation. Given the previously demonstrated greater stability towards basic/nucleophilic conditions of arylgermanes as compared to arylsilanes/stannanes, these reactions significantly expand the utility of group 14 acyldemetalation in synthesis. This is exemplified by the cleavage of Ge-based linker models for solid-phase synthesis (SPS). Georg Thieme Verlag Stuttgart.
- Spivey, Alan C.,Gripton, Christopher J. G.,Noban, Catherine,Parr, Nigel J.
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p. 2167 - 2170
(2007/10/03)
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- Dimeric α-lithio-2,6-dimethylstyrene
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Improved preparations of 2,6-dimethylstyrene (5) and its abromo derivative (10) are described. The Br/Li exchange reaction of 10 provides single crystals of the title compounds 11 or 12, which were characterized as disolvated dimers by X-ray analyses. A similar dimer persists in diethyl ether, tertbutyl methyl ether, and toluene at all accessible temperatures, with significant lithiation NMR shifts (relative to 5) partially due to charge delocalization from the sp2-carbanionic center. Some NMR coupling constants are typical of the dimeric aggregate. The configurational (E,Z) lability is quantified in toluene solution. VCH Verlagsgesellschaft mbH.
- Knorr, Rudolf,Behringer, Claudia,Noeth, Heinrich,Schmidt, Martin,Lattke, Ernst,Raepple, Edith
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p. 585 - 592
(2007/10/03)
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- Competitive acylation of arylstyrylsilanes: Controlling silanucleophile reactivity
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Electrophilic substitution reactions occurred cleanly between acyl cations and arylstyrylsilanes 2-4. With an unsubstituted aryl group, 2 underwent transfer of the styryl group to form styryl ketone 5 as would be predicted from previous kinetic studies. With increasing methyl group substitution of the aryl group, aryl group transfer occurred competitively such that 3 showed a 2:1 preference for destyrylation: dearylation giving 10:11 while 4 underwent exclusive transfer of the mesityl group to give mesityl ketones 6-8. These results are not consistent with electrophilic aromatic substitution reactions of nonsilylated compounds. With increasing methyl group substitution of the aryl group, its reactivity should increase for electronic reasons but not to the extent that is surpasses that of the styryl group. When the silyl group is flanked by methyl groups, however, cleavage of the silicon-aryl bond is additionally facilitated by the relief of steric congestion such that this process occurs preferentially to transfer of the styryl group.
- Brook, Michael A.,Henry, Courtney
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p. 861 - 868
(2007/10/03)
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- Alkenyl bromides by brominative deoxygenation of ketones in one or two steps
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The conversion of ketones into alkenyl bromides is accomplished in one or two steps by 2,2,2-tribromo-2,2-dihydro-1,3,2-benzodioxaphosphole or by the dibromomethyl methyl ether prepared therefrom. Investigations of the scope and limitations provide some hints for the preparative planning and improvement.
- Von Roman,Ruhdorfer,Knorr
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p. 985 - 992
(2007/10/02)
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- Methyl Group Effect on the Proton Affinity of Methylated Acetophenones Studied by Two Mass Spectrometric Techniques
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The proton affinities (PA) of all isomeric dimethylacetophenones were determined using the "kinetic method" with a tandem mass spectrometer and by measurements of the proton transfer equilibrium in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry.For both methods acetophenone and p-methylacetophenone, with well known PA values, were used as reference bases.Both methods yielded identical PA values for all dimethylacetophenones.The PA of the dimethylacetophenones were in a narrow range between 872 and 880 kJ mol-1 except for 2,6-dimethylacetophenone, for which a PA of 856 kJ mol-1 was found.The results are discussed in terms of possible mesomeric structures stabilizing the positive charge with regard to the substitution pattern in the phenyl ring.Obviously, the significant smaller PA of 2,6-dimethylacetophenone compared with the other isomers is due to the distortion of the conjugation of the C-O double bond with the aromatic ? system.
- Kukol, A.,Strehle, F.,Thielking, G.,Gruetzmacher, H.-Fr.
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p. 1107 - 1110
(2007/10/02)
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- Vinyl Cation Intermediates in Solvolytic and Electrophilic Reactions. 1. Solvolysis of α-Arylvinyl Derivatives
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The solvolysis of 16 α-arylvinyl tosylates, bromides, and chlorides has been investigated in various alcohol-water mixtures and in acetic acid at several temperatures.All substrates were substituted with either 2-methyl or 2,6-dimethyl groups to accelerate the rates of reaction.The major or exclusive product isolated in most cases was the acetophenone arising from hydrolysis of the expected enol ethers or acetates during workup.The kinetics were simple first order in the vast majority of cases, with excess base added to prevent side reactions.Leaving group effects, Winstein-Grunwald m values, Schleyer Q values, and effects of solvent nucleophilicity all point to a limiting SN1 ionization generating a vinyl cation intermediate, in which there is little rear-side nucleophilic assistance by solvent.Substituent effects led to ρ values in the range -3.9 to -5.3 vs. ?+.Activation parameters are typical for an SN1 process, and ΔS% is insensitive to the presence of zero, one, or two o-methyl groups, as are the effects of solvent polarity on the rates.The results should therefore be directly comparable with other solvolytic or electrophilic reactions generating formally similar vinyl cation intermediates.
- Yates, Keith,Mandrapilias, George
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p. 3892 - 3902
(2007/10/02)
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