Search PubMed⌕ Search

Biomedical subjects

Jun-Ichi Yoshida

Publications and source records attributed to Jun-Ichi Yoshida.

17 recordsLinked to original sources
PubMed2006

Sequential Pd- and Rh-catalyzed three-component cyclization with allenylboronate platform.

[reaction: see text] A novel three-component cyclization using allenylboronate ester is described. A three-component assembly of allenylboronate ester, aryl iodides, and stabilized carbon nucleophiles took place in the presence of palladium catalyst, furnishing functionalized alkenylboronate esters with high regio- and stereoselectivity. A Rh-catalyzed cyclization of the resultant three-component products then afforded interesting carbocyclic frameworks efficiently.

Journal Article↗
PubMed2006

Catalytic four-component assembly based on allenylboronate platform: new access to privileged allylic amine structures.

We developed a novel palladium-catalyzed four-component assembly based on allenylboronate platform, by which privileged allylic amine structures can be constructed in a regioselective, stereoselective, and diversity-oriented manner. The boryl group acts not only as a useful group that can be transformed to various functional groups afterward but also as a stereochemical controller in the generation of key (pi-allyl)palladium intermediates. A short synthesis of rolipram (selective phosphodiesterase-4 inhibitor) is also demonstrated.

Journal Article↗
PubMed2005

Control of extremely fast competitive consecutive reactions using micromixing. Selective Friedel-Crafts aminoalkylation.

Friedel-Crafts reactions of aromatic and heteroaromatic compounds with an N-acyliminium ion pool were studied. The reaction of 1,3,5-trimethylbenzene in a batch reactor gave rise to the selective formation of a monoalkylation product (69%). Presumably, the second alkylation is slower than the first alkylation because of the protonation of the monoalkylation product that decreases its reactivity. The reaction of 1,3,5-trimethoxybenzene, however, gave rise to the formation of both monoalkylation (37%) and dialkylation (32%) products. Disguised chemical selectivity due to faster reaction than mixing seems to be responsible for the lack of selectivity. The use of micromixing was found to be quite effective to solve this problem to increase the selectivity. The monoalkylation product was obtained in 92% yield together with a small amount of the dialkylation product (4%). The reaction with various aromatic and heteroaromatic compounds revealed that the low mono/dialkylation selectivity was observed only for highly reactive aromatics. In such cases, the use of micromixing was quite effective to improve the selectivity. On the basis of micromixing, the selective sequential dialkylation using two different N-acyliminium ions was achieved. CFD simulations using a laminar flow and finite-rate model are consistent with the experimental observations and clearly indicate the importance of mixing.

Alkylation↗
PubMed2004

Three-component coupling based on the "cation pool" method.

Sequential one-pot three-component coupling reactions have been developed based on the "cation pool" method. An N-acyliminium ion generated by the "cation pool" method adds to an electron-rich carbon-carbon double bond, such as enamine derivatives and vinyl sulfides, to form the second "cation pool". The addition of nucleophiles such as allylsilanes, enol silyl ethers, Grignard reagents, and organoaluminum compounds led to the formation of the corresponding three-component coupling products.

Journal Article↗
PubMed2004

Highly versatile organostibine mediators for living radical polymerization.

A new versatile method for conducting living radical polymerization has been developed in which organostibines induce consecutive group-transfer radical reactions with alkenes. The method has been successfully applied, for the first time, to the controlled polymerization of both conjugated and unconjugated vinyl monomers, and the desired polymers with predetermined molecular weight and low polydispersity index were obtained in excellent yields. This characteristic feature of this method is exemplified in the first synthesis of block copolymers composed of conjugated and unconjugated monomers, which would be of great importance as functional smart organic nanomaterials.

Journal Article↗
PubMed2003

Mechanism-based invention of high-speed living radical polymerization using organotellurium compounds and azo-initiators.

Kinetic analysis reveals the existence of two competing pathways in the organotellurium-mediated living radical polymerization (TERP) at elevated temperature. The rate-determining step, namely, the thermal dissociation process, could be bypassed by the addition of conventional radical initiators, and the polymerization proceeded at low temperature by the degenerative transfer-mediated polymerization. The polymerization conditions are applicable to a variety of vinyl monomers, and the desired polymers form in a highly controlled manner.

Journal Article↗
PubMed2003

Palladium-catalyzed rearrangement/arylation of 2-allyloxypyridine leading to the synthesis of N-substituted 2-pyridones.

[reaction: see text] The Pd-catalyzed one-pot rearrangement/arylation of 2-allyloxypyridine is described. The catalyst/base combination of Pd[P(t-Bu)(3)](2)/Ag(2)CO(3) was found to be optimal for this one-pot rearrangement/arylation. The initial rearrangement of 2-allyloxypyridine was found to be catalyzed by both Pd(0) and Pd(II) complexes with different mechanisms.

Journal Article↗
PubMed2003

Efficient and rapid C-Si bond cleavage in supercritical water.

Arylsilanes, alkenylsilanes, allylic silanes, and alkylsilanes were found to undergo extremely facile and rapid C-Si bond cleavage in supercritical water. The rapid C-Si bond cleavage occurred even with robust unactivated tetraalkylsilanes. The control experiments revealed the dramatic difference between supercritical and subcritical conditions and that between supercritical water and supercritical methanol, attesting to a unique reactivity of supercritical water in C-Si bond cleavage.

Journal Article↗
PubMed2003

"N-acyliminium ion pool" as a heterodiene in [4 + 2] cycloaddition reaction.

[reaction: see text] An N-acyliminium ion pool was found to undergo cycloaddition reaction with a variety of dienophiles such as alkenes and alkynes. A concerted mechanism seems to be most likely for alkyl-substituted alkenes as suggested by the DFT calculations, whereas a stepwise mechanism plays the major role for aryl-substituted alkenes. It is also noteworthy that the present study demonstrates the potential of the combination of the cation pool method and the micromixing in both mechanistic and synthetic aspects.

Journal Article↗
PubMed2002

Electrochemistry of chalcogenoglycosides. Rational design of iterative glycosylation based on reactivity control of glycosyl donors and acceptors by oxidation potentials.

Electrochemical properties of various para-substituted phenylthio-, phenylseleno-, and phenyltelluroglucopyranosides bearing acetyl, benzoyl, and benzyl protecting groups have been investigated to estimate the reactivity of chalcogenoglycosides toward electrochemical glycosylations. The oxidation potential of the chalcogenoglycosides shows good correlation with the ionization potential of chalcogen atoms, and decreases in the order thio-, seleno-, and telluroglycosides. It is also affected by the para-substituents, and the substitution effect correlates very well with the HOMO energy of para-substituted benzenechalcogenol and with the Hammett sigma p + value. Electrochemical glycosylation of telluroglycosides has been examined, and it was found that the use of an undivided cell is more effective than the use of a divided cell. Selective activation of the chalcogenoglycosides in bulk electrolysis based on their oxidation potentials has been examined, and the relative reactivity of the telluroglycosides can be estimated from their oxidation potentials. However, the relative reactivity of selenoglycosides in the preparative glycosylation was rather insensitive to the oxidation potential values.

Chalcogens↗
PubMed2002

Tailored synthesis of structurally defined polymers by organotellurium-mediated living radical polymerization (TERP): synthesis of poly(meth)acrylate derivatives and their di- and triblock copolymers.

The organotellurium-mediated living radical polymerization (TERP) method allows the synthesis of various polyacrylate and polymethacrylate derivatives with precise control of molecular weight and with defined end groups. The method can be applied to the synthesis of AB-diblock and ABA- and ABC-triblock copolymers composed of different families of monomers.

Journal Article↗
PubMed2002

A general and straightforward route toward diarylmethanes. Integrated cross-coupling reactions using (2-pyridyl)silylmethylstannane as an air-stable, storable, and versatile coupling platform.

[reaction: see text] Pharmacologically important diarylmethane structures have been prepared in a straightforward manner through sequentially integrated Pd-catalyzed cross-coupling reactions. (2-Pyridyl)silylmethylstannane was found to be an air-stable, storable, and versatile coupling platform in this synthetic strategy.

Journal Article↗
PubMed2002

The use of hydrophilic groups in aqueous organic reactions.

The representative examples of beneficial effects of hydrophilic groups in aqueous organic reactions are described, including the Diels-Alder reactions, hetero Diels-Alder reactions, Claisen rearrangement, radical reactions, and transition metal-catalyzed reactions. Although the low solubility of organic molecules in water has been a bane in aqueous organic reactions, the incorporation of hydrophilic groups into the substrate structure can overcome the solubility problem and at the same time enhance the hydrophobic effect. In some cases, interesting micellar effects are observed because of the amphiphilic natures of such molecules. The emerging concept of "removable hydrophilic group," in which the solubility problems have been alleviated, yet the initial product can still be transformed into a variety of products with the removal of the hydrophilic groups, is also described.

Carbohydrates↗