Jürgen Martens

Enantioselective catalytic borane reductions of achiral ketones: Syntheses and application of two chiral β-amino alcohols from (S)-2-indoline carboxylic acid

Abstract The synthesis of (S)-α,α-diphenyl-(indolin-2-yl)methanol 1 makes available the chiral oxazaborolidine 2 which is an excellent catalyst for borane reduction of prochiral ketones to chiral secondary alcohols, e.g. acetophenone, in high optical purity The new chiral auxiliary 1 is sythesized from (S)-2-indoline carboxylic acid in a two step procedure. (S)-(Indolin-2-yl)methanol 3 is converted to the oxazaborolidine 4 which served also as an enantioselective catalyst in the reduction of aromatic ketones with BH3·THF.

First catalytic asymmetric hydrophosphonylation of cyclic imines: Highly efficient enantioselective approach to a 4-thiazolidinylphosphonate via chiral titanium and lanthanoid catalysts

The catalytic and enantioselective hydrophosphonylation of a cyclic imine, namely the 3-thiazoline 1, is described. We have discovered a highly efficient enantioselective de novo approach to the pharmaceutically interesting 4-thiazolidinylphosphonate 2 using either titanium or lanthanoid chiral catalysts, which gives excellent enantiomeric purities (up to 98 %ee) and high chemical yields.

Resolution of enantiomers of ibuprofen by liquid chromatography: a review.

Ibuprofen is one of the most effective and widely used non-steroidal analgesic and anti-inflammatory agent. It is marketed as a racemic mixture though it is known that the pharmacological activity resides in the (S)-(+)-enantiomer only. Several direct/indirect liquid chromatographic methods involving a variety of chiral/achiral phases along with their possible role in resolution, chiral and achiral agents used for derivatisation have been discussed with special reference to ibuprofen, and mentioning their application to the resolution of other 2-aryl-propionic acids/profens.

Direct resolution of enantiomers by impregnated TLC

Direct resolution of enantiomers has acquired greater analytical importance. Of various chromatographic techniques, TLC continues to enjoy considerable reputation for the purpose. The present paper deals with an important and yet less explored aspect of TLC i.e. impregnation. Methods of impregnation of thin layer material with a variety of reagents and the role of impregnating reagents in resolving compounds on these layers, with special reference to main/basic approaches of impregnation as applied to direct enantiomeric resolution, are discussed.

Catalytic enantioselective addition of diethylzinc to aldehydes : application of a new bicyclic catalyst

Abstract The optically active β-amino alcohol (1 R ,3 R ,5 R )-3-(diphenylhydroxymethyl)-2-azabicyclo[3.3.0]octane (1 R ,3 R ,5 R )- 1 derived from a bicyclic proline analogue catalyzes the enantioselective addition of diethylzinc to various aldehydes. The resulting chiral secondary alcohols are obtained in high optical yields up to 100 % under mild reaction conditions. The bicyclic catalyst gives much better results than the corresponding ( S )-proline derivative ( S )- 4 .

Enantioselective Catalytic Borane Reductions of Achiral Ketones: Synthesis and Application Of New Catalysts Prepared from (S)-Tert-Leucine and (S)-Azetidinecarboxylic Acid

Abstract Enantiocontrolled reduction of prochiral ketones with borane in the presence of homochiral amino alcohols 1—3 as enantioselective catalysts afforded the corresponding secondary alcohols in moderate to high (69 to >99 %) optical yields.

L-cysteine-derivatives in asymmetric synthesis: Preparation of two new chiral β-amino alcohols and their application in the enantioselective catalytic reduction of prochiral aromatic ketones with borane

Abstract The optically active β-amino alcohols 1 and 2 derived from S -alkylated L-cysteine 3 and 4 respectively catalyze the enantioselective reduction of unsymmetrical ketones with borane. The resulting chiral secondary alcohols are obtained in high optical yields up to 100% under mild reaction conditions.

Diastereoselective synthesis of vinylmorpholines by palladium-catalyzed tandem allylic substitutions using enantiopure aminoalcohols as bifunctional nucleophiles

Abstract Enantiopure vinylmorpholines have been prepared by a diastereoselective disubstitution ( de up to 92%) of (Z) ROCH 2 CHCHCH 2 OR (R = Ac, CO 2 Me) by aminoalcohols in the presence of palladium catalysts.

Catalytic enantioselective addition of diethylzinc to aldehydes: Synthesis and application of a new cyclic catalyst

Abstract The new optically active b-amino alcohol ( S )-1-methyl-2-(diphenylhydroxymethyl)azetidine ( S )- 4 derived from ( S )-azetidinecarboxylic acid ( S )- 1 catalyzes the enantioselective addition of diethylzinc to various aldehydes. The resulting chiral secondary alcohols 5a–h are obtained in high optical yields up to 100% under mild reaction conditions.

Enantioselective catalytic reductions of ketones: Synthesis and application of a new structurally rigid bicyclic catalyst

Abstract The oxazaborolidine catalyst from (1 R ,3 R ,5 R )-3-(diphenlhydroxymethyl)-2-azabicyclo[3.3.0]-octane (1 R ,3 R ,5 R )- 3 has been used in the enantioselective homogenous reductions of prochiral ketones with borane.