Hisao Nishiyama

Cooperative Catalytic Activation of Si―H Bonds by a Polar Ru―S Bond: Regioselective Low-Temperature C—H Silylation of Indoles under Neutral Conditions by a Friedel—Crafts Mechanism

Merging cooperative Si-H bond activation and electrophilic aromatic substitution paves the way for C-3-selective indole C-H functionalization under electronic and not conventional steric control. The Si-H bond is heterolytically split by the Ru-S bond of a coordinatively unsaturated cationic ruthenium(II) complex, forming a sulfur-stabilized silicon electrophile. The Wheland intermediate of the subsequent Friedel-Crafts-type process is assumed to be deprotonated by the sulfur atom, no added base required. The overall catalysis proceeds without solvent at low temperature, only liberating dihydrogen.

Iron‐ and Cobalt‐Catalyzed Asymmetric Hydrosilylation of Ketones and Enones with Bis(oxazolinylphenyl)amine Ligands

Chiral bis(oxazolinylphenyl)amines proved to be efficient auxiliary ligands for iron and cobalt catalysts with high activity for asymmetric hydrosilylation of ketones and asymmetric conjugate hydrosilylation of enones.

Synthesis and use of bisoxazolinyl-phenyl pincers

The bisoxazolinyl-phenyl (Phebox) ligand is an example of an N,C,N tridentate (pincer type) ligand, which has a central carbon-metal covalent bond and two oxazolines. In this tutorial review, synthetic methods to prepare bisoxazolinyl-phenyl derivatives and their transition-metal complexes including rhodium, iridium, platinum, palladium, nickel and copper, are summarized. In addition, several applications to homogeneous and asymmetric catalysis with chiral bisoxazolinyl-phenyl metal complexes have been reviewed.

Remote electronic control in asymmetric cyclopropanation with chiral Ru-pybox catalysts

Abstract Electronic control by remote substitents far from a catalytically active center was found in an asymmetric cyclopropanation of olefins and diazoacetates with the ruthenium catalysts of chiral 4-substituted bis(4′-isopropyloxazolinyl)pyridine, 4-X-pybox. It was found that electron-withdrawing groups increase the catalytic activity, but electron-donating groups decrease it. The enantiomer ratios of the product cyclopropanes with the electron-withdrawing groups, X = Cl and COOMe, are higher than those with the electron-donating groups, X = OMe and NMe 2 . The enantiomer ratios of the ethyl and l -menthyl cyclopropanes were corelated toward Hammetts σ para values to give positive ϱ values, 0.365 for trans -ethyl ester, 0.486 for cis -ethyl ester, 0.517 for trans - l -menthyl ester, and 0.517 for cis - l -menthyl ester. However, the trans:cis ratios of the products were not affected by their substitutents, ca. 90:10 for ethyl diazoacetate and ca. 96:4 for l -menthyl diazoacetate. Intramolecular cyclopropanation clearly gave a similar trend.

Bis(1-3:5-6-η-cyclooctadienyl)ruthenium: Preparation, NMR spectroscopy, and isomerization to (η6-1,3,5-cyclooctatriene)(1-2:5-6-η-1,5-cyclooctadiene)ruthenium via the activation of a CH bond

Abstract The complex Ru(1-3:5-6-η-C 8 H 11 ) 2 (II) was prepared by the reduction of ruthenium trichloride hydrate with zinc in the presence of 1,5-cyclooctadiene at room temperature. Complex II, isomerized to Ru(η 6 -C 8 H 10 )(1-2:5-6-η-C 8 H 12 ) (I) at 70°C by the migration of a hydrogen atom from one l-3:5-6-η-C 8 H 11 ligand to the other. The 1 H and 13 C NMR spectral evidence including selective irradiation studies suggests unsymmetrical coordination of the olefinic moiety of the 1-3:5-6-η-C 8 H 11 ligand in the complex II.

Preparation and synthetic application of 2-bromoallyltrimethylsilane as a 1-hydroxymethylvinyl anion equivalent

Abstract The 1-trimethylsilylmethylvinyl group, as a 1-hydroxymethylvinyl equivalent, was readily introduced to epoxides with the corresponding Grignard reagent derived from 2-bromoallyltrimethylsilane. Obtained 2-(2-hydroxy-ethyl)-allylsilanes were converted to α-methylene-γ-lactones via diols.

Asymmetric beta-boration of alpha,beta-unsaturated carbonyl compounds promoted by chiral rhodium-bisoxazolinylphenyl catalysts.

Chiral rhodium-bisoxazolinylphenyl acetate complexes exhibited high catalytic activity for the beta-boration of alpha,beta-unsaturated carbonyl compounds with bis(pinacolato)diboron in the presence of sodium t-butoxide with enantioselectivity up to 97%.

Asymmetric Diboration of Terminal Alkenes with a Rhodium Catalyst and Subsequent Oxidation: Enantioselective Synthesis of Optically Active 1,2-Diols†

Pin it down: A highly enantioselective diboration of terminal alkenes with chiral 1 and bis(pinacolato)diboron (B2 pin2 ) was realized. Subsequent oxidation of the diboron adducts with sodium peroxoborate readily gave the corresponding optically active 1,2-diols in high yields and high enantioselectivities.

Reductive Aldol, Michael, and Mannich Reactions

Transition metal-catalyzed conjugate reductions of α,β-unsaturated carbonyl compounds mediated by hydride sources, such as hydrosilanes or molecular hydrogen, enable in-situ generation of transition metal enolates. These are capable of coupling to aldehydes, ketones, α,β-unsaturated carbonyl compounds, or imines to furnish the corresponding aldol, Michael, or Mannich products, respectively. In these carbon–carbon coupling reactions, the transition metal catalyst and stoichiometric reductant, assisted by various ligands or chiral auxiliaries, may promote high levels of stereo- and enantioselectivity. In this review, the various metal catalysts that promote reductive aldol coupling and related processes are surveyed from the perspective of synthetic organic chemistry, from historical findings to recent developments.

Asymmetric direct alkynylation catalyzed by chiral Ru-bis(oxazolinyl)phenyl complexes.

Propargylic alcohols were obtained with excellent enantioselectivities in the asymmetric direct alkynylation of aldehydes using 5 mol % of chiral ruthenium complexes containing the chiral bis(oxazolinyl)phenyl ligand.