In O Kim

Polymeric cinchona alkaloids for the heterogeneous catalytic asymmetric dihydroxylation of olefins: The influence of the polymer backbone polarity on the compatibility between polymer support and reaction medium

Abstract Heterogeneous catalytic asymmetric dihydroxylation of olefins using homo- and co-polymeric cinchona alkaloids has been reported. The benzoate type homopolymers 2a, b showed high enantioselectivity in the heterogeneous ADH reactions, but their catalytic efficiency was largely dependent on the solvent system which may relate to the accessibility of the active catalytic site. The influence of polymer backbone polarity on the compatibility with the reaction medium was investigated using copolymers 3a, b and 4 having polar polymer backbone. The reaction rates and optical yields were dramatically increased by increasing the polarity of the polymer backbone in NMO- acetone H 2 O system.

Synthesis of new C2-symmetric bioxazoles and application as chiral ligands in asymmetric hydrosilylation

Abstract New C2-symmetric chiral (4S,4′S)-bioxazoles 3a and 3b, possessing chirality on their backbone, were synthesized efficiently starting from L-tartaric acid. The structure of 3a was determined by X-ray crystal structure analysis. With these novel chiral bioxazole ligands, as a preliminary investigation for their effects on the enantioselectivity, rhodium(I)-catalyzed enantioselective hydrosilylations of acetophenone were carried out.

A new C2-symmetric chiral bisphosphine ligand containing a bioxazole backbone: highly enantioselective hydrosilylation of ketones

Abstract C 2 -Symmetric (4 S ,4′ S )-2,2′-bis( o -diphenylphosphinophenyl)-4,4′,5,5′-tetrahydro-4,4′-bi(1,3-oxazole) ( 1 , Phos-Biox) has been designed and synthesized as a chiral ligand for metal-catalyzed reactions. The Phos-Biox 1 was found to be an efficient ligand for rhodium(I)-catalyzed asymmetric reduction of prochiral acetophenones with diphenylsilane to give optically active secondary alcohols of up to 97% ee.

Preparation of Ethyl (R)-3-hydroxy-4-chlorobutyrate by Selective Reduction of (R)-4-(Trichloromethyl)-oxetan-2-one: Key Intermediate to (R)-Carnitine and (R)-4-Amino-3-hydroxybutyric Acid

Abstract Selective reduction of (R)-4-(trichloromethyl)-oxetan-2-one in ethanol by catalytic hydrogenation on Pd-C in the presence of KOAc gave directly ethyl (R)-3-hydroxy-4-chlorobutyrate, which can be used as a key intermediate for the synthesis of some biologically active γ-amino-β-hydroxy amino acids, (R)-carnitine and γ-amino-β-hydroxy amino acid (R)-GABOB).

Polymeric cinchona alkaloids as catalysts in the enantioselective 2,2-cycloaddition reaction of ketene and chloral

Abstract Poly(cinchona alkaloid- co -acrylonitrile) 1a – d and poly(cinchona alkaloid aciylate) 2a – b catalyze the enantioselective cycloaddition of ketene to chloral for the preparation of ( R )- and ( S )-β-(trichloromethyl)-β-propiolactone. Copolymers 1a – d showed relatively lower catalytic activity with moderate enatioselectivity (22–59% e . e .), while homopolymers 2a – b gave similar catalytic activity and enatioselectivity (60–94% e . e .) compared to those of their monomeric alkaloids as catalysts. The polymeric effect was observed with poly(acryloyl quinidine) 2a as catalyst to get the best enantioselectivity of 94% e . e . at the tempereture −30°C.

Chromatographic resolution of racemic α-halocarboxylic acids and O-substituted α-hydroxycarboxylic acids via diastereomeric N-acyloxazolidinones

Abstract Diastereomeric pairs of N-acyloxazolidinones, derived from (4 R ,5 S )-4-methyl-5-phenyl-2-oxazolidinone (as a chiral derivatizing agent) and racemic α-halocarboxylic acids or O-substituted α-hydroxycarboxylic acids, were separated chromatographically on a large preparative scale and showed appreciable degrees of NMR-shift difference. The origins of the chromatographic separability of these diastereomers are discussed.

Asymmetric Hydrocyanation of 3-Phenoxybenzaldehyde Catalyzed by Polymer-Bound Cyclic Dipeptides

Abstract The polymer-bound catalyst 3a-e inserted some spacer ([-NHCO(CH2 10- n; n = 0,1,2,3,4) connecting the catalytic moiety [cyclo(-(S)-Phe-(S)-His)], [(S,S)-1] and 2% cross-linked Merrifields polymer, have been prepared and their catalytic efficiency for the enantioselective hydrocyanation of 3-phenoxybenzaldehyde was studied.