Xingshu Li

Enantioselective alkynylation of aromatic aldehydes catalyzed by new chiral amino alcohol-based ligands

Abstract A series of binaphthyl-derived amino alcohols were synthesized and used as catalytic ligands in the asymmetric alkynylation of aromatic aldehydes in the presence of a dialkylzinc reagent. The alkynylation of a variety of aromatic aldehydes gave the corresponding chiral propargylic alcohols in 61–93% e.e.

Highly enantioselective hydrogenation of enamides catalyzed by rhodium–monodentate phosphoramidite complex

The monodentate phosphoramidite ligand monophos was used in the Rh-catalyzed asymmetric hydrogenation of enamides to give high enantioselectivities (up to 96% ee).

New 1,3-amino alcohols derived from ketopinic acid and their application in catalytic enantioselective reduction of prochiral ketones

Abstract New 1,3-amino alcohols, (1 S ,2 S )- and (1 S ,2 R )-1-hydroxylmethyl-2-amino-7,7-dimethyl bicyclo[2,2,1]heptane ( endo - 4 and exo - 4 ), were prepared from ketopinic acid via oximation and reduction. The enantioselective borane reduction of prochiral ketones catalyzed by the borane complex of exo - 4 was examined.

Effective activation of chiral BINOL/Ti(OiPr)4 catalyst with phenolic additives for the enantioselective alkynylation of aldehydes

The activation of chiral titanium(IV) complexes with achiral activators, e.g. phenol, is found to provide higher levels of enantioselectivity than those attained with an enantiopure catalyst in the alkynylations of both aromatic and aliphatic aldehydes.

Bipyridyl-based diphosphine as an efficient ligand in the rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to α,β-unsaturated ketones

Abstract Reactions of α,β-unsaturated ketones with excess arylboronic acids in the presence of a rhodium catalyst generated in situ from Rh(acac)(C 2 H 4 ) and ( S )-P-Phos in dioxane/water at 100°C gave high yields of the corresponding products in up to 99% ee.

Copper-catalyzed enantioselective conjugate addition of triethylaluminum to 2-cyclopentenone

Abstract Bidentate phosphites were prepared starting from BINOL, H 8 -BINOL or 3,3′, 5,5′-tetra- tert- butyl-2,2′-biphenol. Utilization of these ligands in the copper-catalyzed enantioselective conjugate addition of triethylaluminum to 2-cyclopentenone afforded 3-ethylcyclopentanone in up to 94.0% ee.

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%.

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.

An efficient synthesis of chiral homophenylalanine derivatives via enantioselective hydrogenation

Abstract Chiral homophenylalanine derivatives were synthesized via enantioselective hydrogenation of 5a and 5b catalyzed by rhodium complexes bearing chiral phosphine and phosphinite legands. Enantiomeric excesses up to 96.2% were achieved when S -spiroOP( S -1) was used as a chiral ligand under 500 psi of H 2 pressure in acetone.