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_NAr) 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^–1 was observed for a Cu⁰ 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