Search results for "ALK"
showing 10 items of 4314 documents
The ionic liquid effect on the Boulton-Katritzky reaction: a comparison between substrates of different structure
2015
The mononuclear rearrangement of heterocycles, also called Boulton–Katritzky reaction, was studied in ionic liquid solution using N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N′-(4-nitrophenyl)-formamidine as substrate. The investigation was carried out using piperidine as basic catalyst and several ionic liquids differing in both cation and anion structure. Kinetic data collected were compared with the ones previously reported using (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole to have information about the effect due to the different structure of the alkyl chain borne on the substrate. Furthermore, data were analysed on the grounds of polarity, Kamlet–Taft solvent parameters, but taking…
Aggregation processes of perylene bisimide diimidazolium salts
2015
The supramolecular aggregation of three diimidazolium- functionalized perylene bisimides, differing in the alkyl chain length was investigated. These salts form aggregates in solvents like chloroform, dichloromethane, and glycerol. Solvent-, concentration-, and temperature-dependent spectroscopic studies were carried out, evidencing the occurrence of an isodesmic, enthalpy-driven aggregation process, underpinned by p–p stacking and hydrogen bonding. Moreover, dynamic light scattering (DLS) measurements and SEM images revealed that these salts aggregate in chloroform into elongated structures.
Self-assembly of fluorescent diimidazolium salts: tailor properties of the aggregates changing alkyl chain features
2016
Searching for new fluorescent organic salts to be used in biomedical and electrochemical field, we conjugated properties of imidazolium salts with the ones of naphthalene diimide core and we obtained some N,N′-bis-(1-alkyl-3-propylimidazolium)naphthalene diimide diiodides. We took into account alkyl chains going from hexyl to dodecyl, as well as hydrogenated and fluorinated alkyl tails. After determination of their thermal behaviour by differential scanning calorimetry, concentration-, and temperature-dependent spectroscopic studies (UV-vis and fluorescence) were performed evidencing the occurrence of isodesmic and enthalpy-driven self-assembly processes. Properties of aggregates were also …
Current Bioactive Azole-Containing Natural Products
2010
A Polar18F-Labeled Amino Acid Derivative for Click Labeling of Biomolecules
2014
This work describes the synthesis and 18F-labeling of an amino acid based prosthetic group that is able to participate in copper(I)-catalyzed cycloadditions. The prosthetic group can be used for 18F labeling of biomolecules under mild conditions. The synthesis started with L-serine methyl ester, which was derivatized by introducing an alkyne moiety and a leaving group for 18F labeling. Subsequently, 18F labeling as well as deprotection conditions were screened, which resulted in an overall radiochemical yield (RCY) of around 28 %. Furthermore, the 18F-labeled prosthetic group was treated with an azido cyclic Arg-Gly-Asp (cRGD) peptide as a model system in very high RCY of 98 %.
Comparison of spin density calculation methods for various alkyl-substituted 9,10-anthraquinone anion radicals in the solution phase
1996
EPR and ENDOR spectra were recorded for 2-methyl-9,10-anthraquinone (2-methylAQ), 2-ethylAQ, 2-tertbutylAQ and 2,3-dimethylAQ anion radicals in the solution phase. The EPR spectra were simulated with the help of ENDOR data. The experimental isotropic hyperfine coupling constants (IHFCs) were compared with calculated values from semi-empirical INDO, spin-restricted AM1/CI and B3PW91 density-functional methods. The best computational methods for the IHFCs were the semi-empirical AM1/CI method and the B3PW91 density-functional method with a large basis set.
A density functional theory study of the chemoselectivity and regioselectivity of the domino cycloaddition reactions of nitroalkenes with substituted…
2000
The chemoselectivity and regioselectivity of the domino intermolecular [4 + 2]/[3 + 2] cycloaddition reactions of nitroalkenes with substituted alkenes, vinyl ethers as electron-rich alkenes and vinyl ketones as electron-poor alkenes, have been studied using density functional theory (DFT) methods with the B3LYP functional and the 6-31G* basis set. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the vinyl ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intermolecular [3 + 2] cycloaddition reaction with the vinyl ketone. The two consecu…
ChemInform Abstract: Synthesis of Functionalized Indoles with an α-Stereogenic Ketone Moiety Through an Enantioselective Friedel-Crafts Alkylation wi…
2010
Chiral complexes of BINOL-based ligands with hafnium tert-butoxide catalyze the enantioselective Friedel-Crafts alkylation of indoles with (E)-1,4-diaryl-2-butene-1,4-diones at room temperature, with good yields and ee up to 94%. Hafnium(IV) was found to be a more effective Lewis acid than other frequently used metal ions such as titanium(IV) or zirconium(IV). Unlike the enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated compounds where the stereogenic center is generated in the β-position to a carbonyl group, the Friedel-Crafts alkylation with 2-butene-1,4-diones described here generates an α-stereogenic center with respect to one of the carbonyl groups. This can be…
The construction of quaternary stereocenters by the Henry reaction: circumventing the usual reactivity of substituted glyoxals.
2011
The enantioselective Henry reaction between alkyl- and arylglyoxal hydrates and nitromethane catalyzed by Cu(II)-iminopyridine complexes takes place regioselectively on the ketone carbonyl group to give chiral tertiary nitroaldols with high functional group density and enantiomeric excesses of up to 96 %. Both aromatic and aliphatic glyoxals are suitable substrates for this reaction.
Enantioselective Protonation of the Lithium Transient Enolate of2-Methyltetralone with 2-Sulfinyl Alcohols
2005
A new catalytic cycle for the enantioselective protonation of cyclic ketone enolates with sulfinyl alcohols has been developed. An enol trifluoroacetate that can be easily obtained from the corresponding ketone is used for the first time as an enolate precursor of a cyclic ketone enolate. In this method, the achiral alcohol plays two roles: it is involved, as is usual in catalytic asymmetric protonation reactions, in the turnover of the chiral proton source and also in the generation of a transient enolate through the reaction of its corresponding alkoxide with the enol trifluoroacetate precursor. Stereoselectivity is highly dependent on the structure of the achiral alcohol. High levels of …