Masato Kitamura

Enantioselective addition of diorganozincs to aldehydes catalyzed by β-amino alcohols

Abstract Nucleophilic addition of dialkylzincs to aldehydes in hydrocarbon solvents is markedly accelerated by the presence of a catalytic amount of a β-dialkylamino alcohol. Use of certain sterically constrained chiral amino alcohols such as 3-exo-(dimethylamino)isoborneol or 1-t-butyl-2-piperidinoethanol effects highly enantioselective catalysis giving secondary alcohols in up to 99% ee. Dimethyl-, diethyl-, di-n-butyl-, and di-n-pentyl-zincs have been employed for the alkylation of substituted benzaldehydes and some olefinic or aliphatic aldehydes. Configurational correlation between the chiral auxiliary and alkylation products is discussed.

Convenient preparation of binap-ruthenium(II) complexes catalyzing asymmetric hydrogenation of functionalized ketones

Abstract Ligand exchange between [RuCl 2 (benzene)] 2 or RuCl 2 [Sb(C 6 H 5 ) 3 ] 3 and ( R )- or ( S )-BINAP produces BINAP-Ru(II) complexes which act as catalysts for the highly enantioselective hydrogenation of functionalized ketones.

Enantioselective synthesis of β-amino acids based on BINAP—ruthenium(II) catalyzed hydrogenation

Abstract BINAP—Ru(II) catalyzed hydrogenation of β-substituted ( E )-β-(acylamino)acrylic acids allows efficient enantioselective synthesis of β-amino acids. The Z double bond isomers which possess an intramolecular hydrogen bond between amide and ester groups are more reactive but are hydrogenated with poor enantioselectivity. BINAP—Rh(I) complexes afford only moderate stereoselectivity with the opposite sense of enantioselection.

A practical asymmetric synthesis of carnitine

Abstract The first efficient chemical synthesis of (R)-carnitine has been accomplished on the basis of homogeneous enantioselective hydrogenation of ethyl 4-chloro-3-oxobutanoate.

Enantioselective synthesis of 4-substituted γ-lactones

Abstract BINAP—Ru(II) catalyzed hydrogenation of prochiral 4-oxo carboxylic esters and o -acylbenzoates gives either enantiomer of the corresponding γ-lactones in > 98% enantiomeric excesses.

Dynamic kinetic resolution in BINAP—ruthenium(II) catalyzed hydrogenation of 2-substituted 3-oxo carboxylic esters

Abstract BINAP—Ru catalyzed hydrogenation allows efficient dynamic kinetic resolution of certain 2-substituted 3-oxo carboxylic esters having cyclic structures to lead to the alcoholic products in high enantiomeric and diastereomeric excesses.

Conjugate addition of diorganozincs to α,β-unsaturated ketones catalyzed by a copper(I)-sulfonamide combined system

Abstract In the presence of a Cu(I)N-monosubstituted sulfonamide combined catalyst system, diorganozincs react with α,β-unsaturated ketones to generate Zn enolates, which may be hydrolyzed, giving the β-substituted ketones, or used for further aldol reaction or Pd(0)-catalyzed reaction with allyl acetate leading to the regiospecific α,β-vicinal condensation products.

Asymmetric addition of dialkylzincs to benzaldehyde derivatives catalyzed by chiral β-amino alcohols. Evidence for the monomeric alkylzinc aminoalkoxide as catalyst

Abstract 3- exo -(Dimethylamino)isoborneol efficiently promotes the asymmetric addition of dialkylzincs to aldehydes. In order to characterize the catalytic organozinc species, relative reactivities of various substituted benzaldehydes and organozincs have been examined under enantiopure and racemic conditions. The relative rates are not affected by the enantiomeric purity of the amino alcohol. The Hammett plots of methylation of p -substituted benzaldehydes gave a ϱ value of +1.2. Methylation of o -methylbenzaldehyde is slower than that of benzaldehyde by a factor of 2.3. Relative reactivities of (CH 3 ) 2 Zn, (C 2 H 5 ) 2 Zn, and ( n -C 4 H 9 ) 2 Zn with benzaldehyde were 1:21:8. The results strongly support the mechanism involving a monomeric alkylzinc aminoalkoxide as catalyst.

Kinetic resolution of 4-hydroxy-2-cyclopentenone by rhodium-catalyzed asymmetric isomerization

Abstract Cationic Rh—BINAP complexes catalyze isomerization of racemic 4-hydroxy-2-cyclopentenone to 1,3-cyclopentanedione with 5:1 enantiomeric discrimination.

General asymmetric synthesis of benzomorphans and morphinans via enantioselective hydrogenation

Abstract A variety of optically active benzomorphans including metazocine and pentazocine as well as dextromethorphan, a morphinan, are obtainable by using the BINAP-ruthenium(II) catalyzed enantioselective hydrogenation as key operation.