Synthesis, resolution, and absolute configuration determination of a vicinal amino alcohol with axial chirality. Application to the synthesis of new box and pybox ligands.

New racemic vicinal amino alcohol derivatives with 4-benzylidenecyclohexane skeleton and axial chirality have been prepared. A preparatively easy and efficient protocol for resolution of the N-benzoylamino alcohol is described. Using a 250 × 20 mm (L × ID) Chiralpak® IA column, and the appropriate mixture of n-hexane/ethanol/chloroform as eluent, both enantiomers of N-benzoylamino alcohol 3 are obtained with >99% enantiomeric excess (ee) by successive injections of a solution of the racemic sample in chloroform.

Michael addition of carbonyl compounds to nitroolefins under the catalysis of new pyrrolidine-based bifunctional organocatalysts.

Novel bifunctional pyrrolidine-based organocatalysts for the asymmetric Michael addition of carbonyl compounds to nitroolefins have been synthesised from homoallylamines, which are easily obtained from (R)-glyceraldehyde as a chiral precursor. Under optimal reaction conditions, these bifunctional organocatalysts showed a high catalytic efficiency (almost quantitative yield in most cases) and stereoselectivity in the Michael addition reactions of a variety of aldehydes (up to 98 : 2 dr and 97% ee) and ketones (up to 98 : 2 dr and 99% ee) to nitroolefins.

High-performance liquid chromatographic enantioseparation of unusual amino acid derivatives with axial chirality on polysaccharide-based chiral stationary phases.

The successful enantioseparation of axially chiral amino acid derivatives containing a cyclohexylidene moiety on an analytical and semipreparative scale was achieved for the first time by HPLC using polysaccharide-based chiral stationary phases. Racemic methyl N-benzoylamino esters, easily obtained by methanolysis of the corresponding 5(4H)-oxazolones, were subjected to chiral HPLC resolution using chiral stationary phases based on immobilized 3,5-dimethylphenylcarbamate derivatives of amylose (Chiralpak(®) IA column) or cellulose (Chiralpak(®) IB column). The behaviour of both selectors under different elution conditions was evaluated and compared.

Stereochemical outcome of copper-catalyzed C-H insertion reactions. An experimental and theoretical study.

The combination of chiral preparative HPLC separation, VCD measurements, and theoretical calculations allows the unambiguous determination of the absolute configuration of the conformationally flexible products of copper-catalyzed carbene insertion reactions. DFT calculations were used to predict the stereochemical outcome of the copper-bis(oxazoline)-catalyzed C-H insertion reaction between methyl diazophenylacetate and tetrahydrofuran and also to predict the absolute configuration of the major stereoisomers derived from the same reaction with different cyclic ethers. These predictions were verified experimentally through NMR and VCD spectroscopy and allowed rationalization of the stereochemical outcome of these reactions without further derivatization of the products, which can be prblematic under certain conditions as described herein.

L- and D-proline adsorption by chiral ordered mesoporous silica.

Chiral ordered mesoporous silica (COMS) was synthesized in the presence of amino acid proline by combining tetraethyl orthosilicate and quaternized aminosilane silica sources. The as-prepared materials were activated by calcination or microwave chemical extraction to remove the organic templates. The powder X-ray diffraction and N2 adsorption characterization revealed in COMS the structural and textural features of MCM-41-type silica.