Michael C. K. Choi

Palladium-catalyzed allylic alkylation of tert-butyl(diphenylmethylene)-glycinate with simple allyl esters under chiral phase transfer conditions

Abstract The first example of palladium-catalyzed allylic alkylation of an imino ester with simple allyl esters in the presence of a chiral quaternary ammonium salt is reported. The presence of molecular sieves was found to have a beneficial effect on the enantioselectivity of the reaction by scavenging water from the system. Alkylated products with e.e.s of up to 61% were obtained.

Synthesis and characterization of cobalt(iii) complexes containing 2-pyridinecarboxamide ligands and their application in catalytic oxidation of ethylbenzene with dioxygenElectronic supplementary information (ESI) available: full experimental and spectroscopic data for all compounds. See http://www.rsc.org/suppdata/cc/b3/b301963b/

Four novel cobalt(III) complexes were found to have high catalytic activities and excellent selectivities in the oxidation of ethylbenzene to acetophenone using O2 as oxidant without need of solvent.

Highly enantioselective hydrogenation of α-dehydroamino acids by rhodium complex with H8-MonoPhos

Abstract H 8 -MonoPhos, a new stable and easily prepared monodentate phosphoramidite ligand, has been synthesized from H 8 -BINOL. The ligand showed extremely highly enantioselectivity of higher than 99.9% e.e. in the asymmetric Rh-catalyzed hydrogenation of α-dehydroamino acids. Our study further supports the new concept that there is no gap in efficiency and enantioselectivity between monodentate and chelating ligands for asymmetric catalysis.

A HIGHLY EFFECTIVE PHOSPHINITE LIGAND DERIVED FROM D-MANNITOL FOR RH-CATALYZED ASYMMETRIC HYDROGENATION

Abstract A novel chiral phosphinite 1,2,5,6-di-isopropylidene-3,4-bis(diphenylphosphino)-D-mannitol was prepared and its rhodium complex was found to be an effective catalyst for the asymmetric hydrogenation of amidoacrylic acid and its derivatives with product ees ranging from 90% to 97%.

The first use of chiral oxazoline ligands in the highly enantioselective diethylzinc addition to diphenylphosphinoyl imines

Abstract A series of chiral oxazolines, which had been conveniently prepared from commercially available (1S,2S)-2-amino-1-phenylpropane-1,3-diol, was applied in the diethylzinc addition to diphenylphosphinoyl imines to give high yields of 68–84% and excellent e.e. values of 90–93%.

H8-MonoPhos and its application in catalytic enantioselective hydrogenation of α-dehydroamino acids

Abstract H 8 -MonoPhos, a new stable and readily soluble monodentate phosphoramidite ligand, has been facilely prepared from H 8 -BINOL. The ligand achieved up to 99.9% ee and 96.7% ee in hydrogenation of dehydroalanine and dehydrohomophenylalanine in a S/C ratio of 500:1, respectively, which are among the best results to date. For dehydrophenylalanine derivatives, it gave good to excellent enantioselectivity. Some factors controlling the enantioselectivity and conversion were examined and are discussed. The interesting effects of ligand/rhodium ratio on the enantioselectivity and conversion were observed, which a mechanism was proposed to explain.

Design, synthesis and structure of new chiral squaric acid monoaminoalcohols and diaminoalcohols and their use as catalysts in asymmetric reduction of ketones and diketones

Abstract Many chiral squaric acid aminoalcohols and C2-symmetric diaminoalcohols have been synthesized and their in situ formed chiral boron heterocycles have been used as catalysts for the enantioselective reduction of prochiral ketones and diketones by borane to give alcohols with up to 99% enantiomeric excess and 99% yield. The effects of solvent, catalyst–substrate ratio and temperature were also investigated.

Heterogeneous asymmetric addition of diethylzinc to aromatic aldehydes catalyzed by Ti(IV)/imine bridged poly(R)-binaphthol

Abstract Heterogeneous asymmetric addition of diethylzinc to aldehydes catalyzed by chiral polymer catalysts has been achieved. The conjugated polymers based on a BINOL skeleton were synthesized in five steps and applied to this reaction with yield and e.e. up to 95 and 84.5%, respectively. These chiral polymers can be easily quantitatively recovered and reused without decreasing of e.e. or catalytic activity.

Catalytic Asymmetric Synthesis of (S)-Acetophenone Cyanohydrin under High Pressure

Abstract The first trimethylsilylcyanation of acetophenone to its ( S )-cyanohydrin was accomplished with e.e. up to 60% in 93% yield at 0.8 GPa, using 0.01 eq. of a reuseable catalyst prepared from ( S )-3,3-dimethyl-1,2,4-butanetriol and titanium isopropoxide. Reactions of 4′-substituted acetophenones to the corresponding cyanohydrins gave lower e.e. and yields.

Highly enantioselective addition of diethylzinc to aldehydes catalyzed by a new chiral C2-symmetric Ti–diol complex

Abstract A novel C2-symmetric chiral diol was synthesized and was found to catalyze the enantioselective addition of diethylzinc to aldehydes to afford optically active secondary alcohols with ees up to 99%.