8 research outputs found
Asymmetric borane reduction using mixtures of homochiral amino alcohol ligands
The asymmetric borane reduction of acetophenone is investigated using mixtures of homochiral β-amino alcohol ligands. With stoichiometric amounts of a mixture of two- or three-amino alcohols, the e.e. remains at the level of the best amino alcohol for a wide composition range. A small but statistically significant enhancement in e.e. is observed when 10 mol% of an amino alcohol mixture of (1S,2R)-1-amino-2-indanol and (S)-phenylglycinol is used as chiral ligand.
“Dutch Resolution”, A New Technology in Classical Resolution
A new method for the resolution of racemates through diastereomeric salt formation is presented. An essential feature of this new method is the use of mixtures of resolving agents. The application of certain mixtures results in an efficient and fast crystallisation of enantiomerically enriched salts. It turns out that these salts still contain a mixture of the resolving agents. Via this new method, referred to as the Dutch Resolution (DR) technology, the success rate in identifying and performing adequate resolutions of racemates has been greatly improved.
Octametallic and hexadecametallic ferric wheels
Jost M, Greie JC, Stemmer N, Wilking SD, Altendorf K, Sewald N. The first total synthesis of efrapeptin C. Angewandte Chemie International Edition. 2002;41(22):4267-4269
A Kinetic Study on the Cu(0)-Catalyzed Ullmann-Type Nucleophilic Aromatic Substitution C–O Coupling of Potassium Phenolate and 4‑Chloropyridine
A parametric
study of the factors that influence C–O bond
formation reactions has been carried out to elucidate the mechanism
by which copper mediates the Ullmann-type nucleophilic aromatic substitution
(S<sub>N</sub>Ar) of 4-chloropyridine with potassium phenolate. Process
conditions such as temperature, reactant concentrations, catalyst
concentration, and amounts of solubilizing additive were varied to
obtain the kinetic data. Both reactant and product concentration were
found to have a significant effect on the reaction rate. An increased
concentration of 18-crown-6 ether, used as an alkali metal solubilizing
agent for potassium phenolate, proved to be effective only for low
conversions, whereas an inhibited phenolate complexation at high product
concentrations was observed. An apparent activation energy of 55 kJ·mol<sup>–1</sup> was observed for a Cu<sup>0</sup> catalyst in the
liquid-phase coupling reaction in a temperature range of 100–150
°C. It was demonstrated that a Langmuir–Hinshelwood kinetic
model is mechanistically most likely to be obeyed for this type of
surface reaction. A maximum adsorption enthalpy on Cu was found for
the product, 4-phenoxypyridine, followed by the reactants phenolate
and 4-chloropyridine, respectively