Motowo Yamaguchi

Palladium-catalyzed asymmetric alkylation via π-allyl intermediate: Acetamidomalonate ester as a nucleophile.

Abstract Asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with sodium salt of acetamidomalonate ester has been carried out in the presence of a palladium catalyst containing ( S )-BINAP to give a chiral α-allyl-αacetamidomalonate ester derivative of high optical purity (94±1% ee).

Palladium-catalyzed asymmetric allylic alkylation using dimethyl malonate and its derivatives as nucleophile

Abstract Palladlum-catalyzed asymmetric allylic alkylatlon of 1,3-dlphenyl-2-propenyl acetate with sodium salt of dimethyl malonate and its derivatives has been successfully carried out in the presence of optically active diphosphine, such as (S)-BINAP. High enantioselectivity of up to 90% ee was obtained with dimethyl malonate.

Mechanism of silver(I)-catalyzed Mukaiyama aldol reaction: active species in solution in AgPF 6 -(S)-BINAP versus AgOAc-(S)-BINAP systems

Abstract Silver(I)-diphosphine complex is an effective catalyst for Mukaiyama Aldol reaction in polar solvents. AgPF6-(S)-BINAP cationic chiral complex indicated a good activity and could afford fairly high enantioselectivity in the reaction of aromatic aldehydes and silyl enol ethers. On the other hand, AgOAc-(S)-BINAP system afforded the aldol product of the absolute configuration opposite to that by AgPF6-(S)-BINAP and very high catalytic activity was shown. The structure and equilibrium state of Ag(I)-BINAP complexes in solution were examined to understand the reaction mechanism. In AgPF6 system [Ag((S)-BINAP)2]PF6 (1a), [Ag((S)-BINAP)]PF6 (1b), [Ag2((S)-BINAP)](PF6)2 (1c) and AgPF6 are present in solution. The active species of the aldol reaction in DMF is [Ag((S)-BINAP)]PF6 (1b), which exists as a minor species in solution. For this cationic Ag(I) catalyst, cyclic transition state containing substrate and silyl enol ether is assumed. In AgOAc-(S)-BINAP system, active species is also monomeric AgOAc((S)-BINAP) (2b) species which exists as a major component in solution and strong interaction was observed with a silyl enol ether. The reaction by AgOAc-(S)-BINAP catalyst is concluded to proceed as follows: nucleophile forms a complex with AgOAc-(S)-BINAP species and is activated. This complex attacks aldehydes to afford aldol adduct via acyclic transition state.

Effective transfer hydrogenation of unsaturated compounds by ruthenium dihydride complex in propan-2-ol

Abstract Ruthenium(II)-hydride complexes were very effective catalysts for the transfer hydrogenation of ketones and imines using propan-2-ol as hydrogen donor in the presence of a base. By using the catalyst dihydridotetrakis(triphenylphosphine)-ruthenium(II), the reduction proceeded effectively in the absence of a base. This ruthenium dihydride catalyst also caused the transfer hydrogenation of benzonitrile to afford benzylamine derivatives albeit in a moderate yield. Isotope labeling experiments in the reaction of N-(2-naphthylmethylidene)benzylamine with this ruthenium dihydride catalyst revealed the hydride transfer from ruthenium hydride to the C N bond of the substrate. In the case of the ruthenium monohydride species, no transfer hydrogenation occurred for ketones, imines and nitrile in the absence of a base except at the C C double bond of conjugated carbonyl compounds.

A novel chiral phosphinediamine ligand and asymmetric hydrogenation of acrylic acid derivatives

Abstract A novel chiral phosphinediamine ligand (PN 2 ) was prepared from ( S )-1-phenylethylamine and dichloroisopropylphosphine. The rhodium-PN 2 catalyst utilizing selective ligation of the amino unit and electrostatic interaction between the ligand and a substrate gave high enantioselectivities up to 92% ee in asymmetric hydrogenations of acrylic acid derivatives.

Asymmetric transfer hydrogenation of aryl-alkyl ketones catalyzed by ruthenium(II) complexes having chiral pyridylmethylamine and phosphine ligands

Abstract In the asymmetric transfer hydrogenation of aromatic ketones using propan-2-ol or a formic acid–triethylamine mixture as hydrogen donor, a mixed ligand ruthenium(II) complex generated in situ from pyridylmethylamine ligands and RuCl2(PPh3)3 or RuHCl(PPh3)3 were examined. In propan-2-ol, the direction of the chirality induction was very sensitive to the aryl substituent of chiral amino unit in pyridylmethylamine ligands. Using HCOOH/NEt3 as hydrogen donor, catalytic activities and enantioselectivities were much improved (up to 100% conversion and 86% e.e.) with ruthenium complex generated from RuHCl(PPh3)3 and 2-pyridylmethyl-1-(R)-phenylethylamine.

Syntheses of mixed-ligand ruthenium(II) complexes with a terpyridine or a tris (pyrazolyl) methane and a bidentate ligand: their application for catalytic hydroxylation of alkanes

Abstract The new mixed-ligand chlororuthenium(II) complexes [RuCl(L) (tpy)]Cln and [RuCl(L) (tpm)]Cln(L = bpy, dmpa or dmgly; n = 0 or 1) were prepared, and the catalytic activity for alkane oxidation using m-chloroperbenzoic acid was examined. Alcohol was the main product: oxidation of adamantane, cyclooctane or ethylbenzene gave hydroxylated products, 1-adamantanol (66%), cyclooctanol (22%) or 1-phenylethanol (48%), respectively.

Preparation and molecular structure of (N-benzyl-1,2-didehydroglycinato) bis(1,10-phenanthroline)-ruthenium(II) chloride: [Ru(N-Bn-gly-H2 (phen)2]Cl

Abstract An α-imino-acidato ruthenium(II) complex, N-benzyl-1,2-didehydroglycinato bis(1,10-phenanthroline) ruthenium(II) complex ([Ru(N-Bn-gly-H2 (phen)2]+), was obtained by controlled-potential anodic oxidation of the corresponding α-amino-acidato ruthenium(II) complex ([Ru(N-Bn-gly) (phen)2]+. The crystal structure of [Ru(N-Bn-gly-H2) (phen)2] Cl·H2O·C2H5OH has been determined by single crystal X-ray diffraction. The benzene ring of the benzyl group of the α-imino-acidato moiety is stacked above one of the phenanthroline rings. The conformation of the benzyl group in solution, estimated by nuclear Overhauser effect measurement, is considered to be similar to that in the crystal.

Electrostatic interaction and induced fitting of the rhodium(I) complex coordinated by diphosphine ligand having an amino group in the diastereoselective hydrogenation of dehydrodipeptides

Rhodium(I)-[2-[2-(dimethylamino)ethyl]-1,3-propanediyl]bis(diphenylphosphine) (DPP-AE) catalyst achieved an effective 1,4-asymmetric induction and afforded high diastereoselectivity (max. 96% d.e.) in the hydrogenation of dehydrodipeptides in protic solvents. Activation parameters indicate the important role of the electrostatic interaction for the asymmetric induction in the hydrogenation. Structural study of the rhodium(I) DPP-AE complex by 31P NMR and circular dichroism spectroscopies indicated that induced fitting of the complex occurred by the electrostatic interaction between the ligand (DPP-AE) and dehydrodipeptide to change the dominant skew-conformation of the complex according to the chiral center of the substrate.

4,6-BIS(IMIDAZOLIO)PYRIMIDINE AS A NEW ANION RECEPTOR

New aryl-oligomer type anion receptors bearing two imidazolium units linked by 6-membered ring aryl spacers at meta-positions have been synthesized. Complexation behavior of the receptors with halide ions (Cl - , Br - , and I - in DMSO-d 6 was investigated by 1 H NMR titrations and semi-empirical calculations (MOPAC AMI). Along with the imidazolium C-H protons, the ortho C-H proton of the central aryl unit forms additional hydrogen bond interaction with guest anion. The receptor with pyrimidine unit exhibited significantly improved anion binding properties.