Atropisomeric biaryl aldehydes undergo diastereoselective condensation with (-)-ephedrine and with a proline-derived diamine, with selectivity highly dependent on solvent, temperature and reaction conditions. Levels of thermodynamic control up to 5:1 may be obtained by heating the diamine with the aldehyde in a sealed tube. Alternatively, crystallisation-induced dynamic transformation allows is...

The synthesis of thioethers starting from alcohols and thiols in the presence of amorphous solid acid catalysts is reported. A silica alumina catalyst with a very low content in alumina gave excellent results in terms of both activity and selectivity also under solvent-free conditions. The reaction rate follows the electron density of the carbinol atom in the substrate alcohol and yields up to ...

Novel Cr(iii) catalysts supported by linear phosph(iii)azanes of the type R(1)R(2)N-P(Ph)-NR(3)-P(Ph)-NR(4)R(5) have been prepared, all of which, upon activation with MMAO-3A, are highly active for ethene tri-/tetramerization with considerable selectivity. The effect of ligand substitution as well as solvent on the catalytic performance has been examined.

Pyrrolizin-3-ones (e.g. 1) can be easily hydrogenated to their hexahydro (pyrrolizidin-3-one) derivatives in the presence of heterogeneous catalysts. Good diastereoselectivity (up to >97:3, depending on catalysts and solvent) can be achieved if the pyrrolizin-3-one is substituted at the 1- (or 7-) position(s), but the selectivity is reduced if both positions are substituted. Subsequent deoxygen...

A p-nitrophenolate-sensitive membrane electrode was constructed by using tetraheptylammonium chloride as an ion-exchanger and o-nitrophenyl phenyl ether as a membrane solvent. The electrode responded to p-nitrophenolate down to 1 ,ƒÊM in a buffer solution of 0.1 M Na2CO3NaHCO3 (pH 10). The selectivity coefficients of the electrode to typical anions increased in the following order: Cl-<NO3< SCN...

A helical aromatic oligoamide foldamer encapsulates tartaric acid with exceptional affinity, selectivity, and diastereoselectivity. The structure of the complex has been elucidated both in solution by NMR spectroscopy and in the solid state by X-ray crystallography, making it possible to rationalize the strong effects observed, particularly the role of hydrogen bonds between the hydroxyl and ca...

Water concentration affects both the enantioselectivity and activity of enzymes in dry organic media. Its influence has been investigated using the hydrocyanation of benzaldehyde catalyzed by hydroxynitrile lyase cross-linked enzyme aggregate (MeHNL-CLEA) as a model reaction. The enzyme displayed higher enantioselectivity at higher water concentration, thus suggesting a positive effect of enzym...

A series of ionophores based on diaza 18-crown-6 units possessing amide and sulfonamide functions were prepared. Their complexing properties were investigated in solvent polymeric membrane electrodes. The influence of the structure of ligands, prepared on the selectivity of complexation, was examined with special respect to lead ions. Substantial changes were observed, when methyl substituent i...

Chemosensitive single-channel fluctuations were observed to be induced in essentially solvent-free lipid bimolecular membranes by the addition of sonicated homogenates of rat olfactory epithelium. The chemosensitive channels were not observed when respiratory epithelium homogenates were used instead. Ionic selectivity is consistent with potassium ions as the charge carrier. These channels may b...

[RhCp*Cl(2)](2) can catalyze the oxidative coupling of secondary isonicotinamides with activated olefins using Cu(OAc)(2) as an oxidant. The selectivity can be controlled by the solvent. In MeCN, the mono-olefination and two-fold oxidation reaction is the major pathway, while in THF this reaction gave mostly diolefination products. In both cases, the coupled products contain an exocyclic C=C bond.