- Keto-enol/enolate equilibria in the 2-acetylcyclopentanone system. An unusual reaction mechanism in enol nitrosation
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The keto-enol equilibrium of 2-acetylcyclopentanone (ACPE) was studied in water by analysing the effect that aqueous micellar solutions produce in the UV absorption spectrum of this compound. Aqueous solutions of anionic, cationic, or nonionic surfactants forming micelles have been used. The quantitative treatment of absorbance changes measured at the maximum absorption wavelength as a function of surfactant concentration gave the keto-enol equilibrium constant, KE. In the same sense, the analysis of spectral changes measured as a function of pH in aqueous basic media allowed us to determine the acidity equilibrium constant, Ka. The combination of both equilibrium constants gives the acidity constant of the enol ionizing as an oxygen acid, pKaE = 7.72 and the acidity constant of the ketone ionizing as a carbon acid, pKaK = 8.12. The kinetic study of the nitrosation reaction of ACPE has been realized in aqueous strong acid media under several experimental conditions. As expected, the reaction is first-order with respect to ACPE concentration, but in sharp contrast to other β-dicarbonyl compounds, the dependence of both [H+] or [X-] (X- = Cl-, Br-, or SCN-) is not simple first-order; instead a fractional order which varied from 1 to 0 was observed. The kinetic interpretation of these experimental facts has been done on the basis of a reaction mechanism that considers the formation of an intermediate in steady-state, which has been postulated as a chelate-nitrosyl complex. The quantitative treatment of the experimental data gave the values of every rate constant appearing in the proposed reaction mechanism.
- Iglesias, Emilia
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Read Online
- Discovery of quinolone derivatives as antimycobacterial agents
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Tuberculosis (TB), an infectious disease caused byMycobacterium tuberculosis(M. tuberculosis), is an important public health issue. Current first-line drugs administered to TB patients have been in use for over 40 years, whereas second-line drugs display strong side effects and poor compliance. Additionally, designing effective regimens to treat patients infected with multi- and extremely-drug-resistant (MDR and XDR) strains of TB is challenging. In this report, we screened our compound library and identified compound1with antituberculosis activity and a minimal inhibitory concentration (MIC) againstM. tuberculosisof 20 μg mL?1. Structure optimization and the structure-activity relationship of1as the lead compound enabled the design and synthesis of a series of quinolone derivatives,6a1-6a2,6b1-6b36,6c1,6d1-6d14,7a1-7a2,7b1-7b2,7c1,8a1-8a5,9a1-9a4and10a1-10a6. These compounds were evaluatedin vitrofor anti-tubercular activity against theM. tuberculosisH37Rv strain. Among them, compounds6b6,6b12and6b21exhibited MIC values in the range of 1.2-3 μg mL?1and showed excellent activity against the tested MDR-TB strain (MIC: 3, 2.9 and 0.9 μg mL?1, respectively). All three compounds were non-toxic toward A549 and Vero cells (>100 and >50 μg mL?1, respectively). In addition, an antibacterial spectrum test carried out using compound6b21showed that this compound specifically inhibitsM. tuberculosis. These can serve as a new starting point for the development of anti-TB agents with therapeutic potential.
- Gao, Chao,Li, Xiao,Liu, Kun-Lin,Teng, Fei,Xiong, Lu,Yu, Luo-Ting
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p. 24095 - 24115
(2021/07/29)
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- Titanium silicates as efficient catalyst for alkylation and acylation of silyl enol ethers under liquid-phase conditions
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The activity of titanium- and tin-silicate samples such as TS-1, TS-2, Ti-β and Sn-MFI has been investigated for acylation and alkylation of silyl enol ethers under mild liquid-phase conditions. Silyl enol ethers successfully react with acetyl chloride and tert-butyl chloride under dry conditions in the presence of above catalysts to produce the corresponding acylated and alkylated products, respectively. In the case of acetylation reaction, two different nucleophiles with carbon-center (C-atom) and oxygen-center (O-atom) in silyloxy group of silyl enol ether reacts with acetyl chloride to give 1,3-diketone and ketene-ester, respectively. The selectivity for alkylation is always ca. 100% and no side products are formed. Among the various solvents investigated, anhydrous THF was found to be the suitable solvent for alkylation; whereas dichloromethane exhibited high selectivity for diketones for acylation. The formation of nucleophiles from silyl enol ethers appears to be the key step for successful acetylation and tert-butylation by nucleophilic reaction mechanism. Sn-MFI showed less activity than that observed over the titanosilicates. The observed catalytic activity is explained on the basis of "oxophilic Lewis acidity" of titanium silicate molecular sieves in the absence of H 2O under dry reaction conditions.
- Sasidharan, Manickam,Bhaumik, Asim
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experimental part
p. 87 - 93
(2011/10/12)
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- Method for preparing chiral diphosphines
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The invention concerns a method for preparing a compound of formula (1) wherein: A represents naphthyl or phenyl optionally substituted; and Ar1, Ar2independently represent a saturated or aromatic carbocyclic group, optionally substituted.
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- Asymmetric hydrogenation method of a ketonic compound and derivative
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The present invention relates to a process for the asymmetric hydrogenation of a ketonic compound and derivative. The invention relates to the use of optically active metal complexes as catalysts for the asymmetric hydrogenation of a ketonic compound and derivative. The process for the asymmetric hydrogenation of a ketonic compound and derivative is characterized in that the asymmetric hydrogenation of said compound is carried out in the presence of an effective amount of a metal complex comprising as ligand an optically active diphosphine corresponding to one of the following formulae: STR1
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- Regioselectivity of Pyrrole Synthesis fromm Diethyl Aminomalonate and 1,3-Diketones: Further Observations
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1,3-Diketones 1 react with diethyl aminomalonate (2) in boiling acetic acid to afford ethyl 2-pyrrolecarboxylates 6.Considerable regioselectivity was noted for the following classes of diketone: 2-acylcyclohexanones 10a,b , 2-acylcyclopentanones 10c,d pyrroles 13a,b>, 1-phenyl-2-alkyl-1,3-alkanediones 17a-d , 3-phenyl-2,4-hexanedione (21a) , 1-phenyl-3-alkyl-2,4-alkanediones 24a,b , and 2,2-dimethyl-3,5-alkanediones 29a,b .The yields varied with the structural class, decreasing with increased steric hindrance.The product structure correlated with the structure of the enolized diketones in the case of the 2-acylcycloalkanones studied.
- Paine, John B.,Brough, Jonathan R.,Buller, Kathy K.,Erikson, Erika E.
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p. 3986 - 3993
(2007/10/02)
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- Acylation of Ketone Silyl Enol Ethers with Acid Chlorides. Synthesis of 1,3-Diketones
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Trimethylsilyl enol ethers of ketones are acylated by a variety of acid chlorides in the presence of zinc chloride or antimony trichloride.The major product of this reaction is the 1,3-diketone resulting from C-acylation.Some O-acylation is observed in most cases.Yields of 1,3-diketones varied but were usually good to excellent.
- Tirpak, Robin E.,Rathke, Michael W.
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p. 5099 - 5102
(2007/10/02)
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- Acylation of Ketone Silyl Enol Ethers with Acetyl Tetrafluoroborate. A Synthesis of 1,3-Diketones
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Silyl enol ethers, obtained by silylation of ketones, are acylated with acetyl tetrafluoroborate to give 1,3-diketones in reasonable yields.Thetert-butyldimethylsilyl enol ether of cyclohexanone gives a nearly quantitative yield of acetylcyclohexanone, while the trimethylsilyl enol ethers of cyclohexanone and other ketones give moderate yields of the corresponding 1,3-diketones.The regiospecificity of the reaction was studied with the isomeric silyl enol ethers of 2-methylcyclohexanone.
- Kopka, Ihor,Rathke, Michael W.
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p. 3771 - 3773
(2007/10/02)
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