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Shū Kobayashi

Publications and source records attributed to Shū Kobayashi.

At least 19 recordsLinked to original sources
PubMed2007

Silica-supported sodium sulfonate with ionic liquid: a neutral catalyst system for Michael reactions of indoles in water.

A neutral catalytic system for Michael reactions of indoles has been developed by combining silica-supported benzenesulfonic acid sodium salt with hydrophobic ionic liquid in water. An efficient hydrophobic environment could be created on the surface of the silica-sodium material under the conditions. Various indole derivatives and alpha,beta-unsaturated carbonyl compounds including some acid-labile substrates were successfully applied to this system with water as the sole solvent to afford the desired Michael adducts in high yields. [structure: see text].

Benzenesulfonates↗
PubMed2007

Surfactant-type Brønsted acid catalyzed dehydrative nucleophilic substitutions of alcohols in water.

A protocol for the dehydrative nucleophilic substitution of benzyl alcohols with a variety of carbon- and heteroatom-centered nucleophiles using dodecylbenzenesulfonic acid (DBSA) as a surfactant-type Brønsted acid catalyst in water has been developed. The reaction system can be applied to the stereoselective C-glycosylation of 1-hydroxy sugars in water. [reaction: see text].

Benzenesulfonates↗
PubMed2006

Novel immobilization method of enzymes using a hydrophilic polymer support.

A novel immobilization of an enzyme with a hydrophilic polymer support in organic solvents has been developed utilizing the "polymer-incarcerated (PI) method", which has been used to immobilize metal catalysts; the kinetic resolution of secondary alcohols was found to proceed more smoothly using immobilized lipases (CALB) than free lipases.

Alcohols↗
PubMed2006

Practical preparation method of polymer-incarcerated (PI) palladium catalysts using Pd(II) salts.

[reaction: see text]. Polymer-incarcerated (PI) palladium catalyst was practically prepared from inexpensive Pd(II) salts and a polystyrene-based copolymer under reducing conditions. Remarkable effects of alkali metal salts on the palladium loading were observed. PI Pd thus prepared showed high catalytic activity in Mizoroki-Heck reactions and Suzuki-Miyaura couplings with a range of substrates including an aryl chloride. In all cases, the Pd catalyst was recovered quantitatively without leaching, and reused several times without significant loss of activity.

Journal Article↗
PubMed2006

Catalytic asymmetric mannich-type reactions activated by ZnF2 chiral diamine in aqueous media.

Catalytic asymmetric Mannich-type reactions of an alpha-hydrazono ester with silicon enolates in aqueous media have been developed by using ZnF2 and chiral diamines as catalysts. In these reactions, both Zn2+ and a fluoride anion were necessary to achieve high yields and enantioselectivities, suggesting a double activation mechanism, in which Zn2+ activates the alpha-hydrazono ester and the fluoride anion simultaneously activates the silicon enolate. When chiral diamine ligands bearing methoxy-substituted aromatic rings were employed, the reactions in aqueous THF were markedly accelerated. Furthermore, the use of these diamines facilitated the asymmetric Mannich-type reactions in water without any organic cosolvents. It is noteworthy that either syn or anti adducts were stereospecifically obtained from (E)- or (Z)-silicon enolates, respectively. Interestingly, these reactions proceeded smoothly only in the presence of water. On the basis of several experimental results, it can be concluded that the reaction mechanism is likely to be a fluoride-catalyzed one, in which the ZnF2 chiral diamine complex is regenerated from the Me3SiF formed during the reaction.

Catalysis↗
PubMed2005

Chiral zirconium catalysts using multidentate BINOL derivatives for catalytic enantioselective Mannich-type reactions; ligand optimization and approaches to elucidation of the catalyst structure.

Catalytic enantioselective Mannich-type reactions of silicon enolates with aldimines were investigated using chiral zirconium catalysts prepared from Zr(O(t)Bu)(4), N-methylimidazole, and newly designed multidentate BINOL derivatives. These new multidentate BINOL ligands were designed on the basis of an assumed transition state structure of a chiral zirconium catalyst derived from two molecules of (R)-6,6'-Br(2)-BINOL. Not only tetradentate BINOL 4 but also tridentate BINOL derivatives were found to be effective, and high enantioselectivities were attained. In a structural study of the most effective zirconium complex prepared from tridentate ligand 6e, several NMR experiments and DFT calculations were carried out. Consequently, the structure of an active catalyst and plausible mechanism of asymmetric induction were elucidated.

Catalysis↗
PubMed2005

Catalytic Pictet-Spengler reactions using Yb(OTf)3.

The catalytic Pictet-Spengler reactions proceeded in high yields with high regioselectivity in the presence of a catalytic amount of Yb(OTf)3 and a dehydrating agent at room temperature. High regioselectivities were obtained in these reactions, and it is suggested that the reactions proceeded under kinetic control.

Catalysis↗
PubMed2005

N-acylhydrazones as versatile electrophiles for the synthesis of nitrogen-containing compounds.

The use of N-acylhydrazones as electrophiles in reactions with nucleophiles has recently made some important advances. N-Acylhydrazones, which can be readily prepared and stored, act as stable imine surrogates in these reactions. The hydrazide products are useful, often chiral building blocks which can be transformed into various nitrogen-containing compounds by cleavage of the N--N bond. The N-acyl groups often play important roles as templates for metal catalysis in controlling stereochemistry. This Minireview summarizes the most recent results of N-acylhydrazone chemistry, and provides an overview of current developments in this field.

Acylation↗
PubMed2005

Hydrogenation reactions using scCO2 as a solvent in microchannel reactors.

We have developed an effective microfluidic system for hydrogenation reactions in scCO(2); the reactions proceeded very rapidly (within 1 second), by making the best use of scCO(2) and utilizing the large specific interfacial area of the microchannel reactor, and high reaction productivity was attained in each channel.

Carbon Dioxide↗