Ryohei Yamaguchi
Kyoto University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Ryohei Yamaguchi.
Journal of the American Chemical Society | 2012
Ryoko Kawahara; Ken-ichi Fujita; Ryohei Yamaguchi
A new catalytic system for the dehydrogenative oxidation of alcohols using a water-soluble Cp*Ir complex bearing a bipyridine-based functional ligand as catalyst has been developed. With this catalytic system, a variety of primary and secondary alcohols have been efficiently converted to aldehydes and ketones, respectively, in aqueous media without using any oxidant. Reuse of the catalyst by a very simple procedure has been also accomplished.
Tetrahedron Letters | 2003
Ken-ichi Fujita; Zhenzi Li; Naohiro Ozeki; Ryohei Yamaguchi
Abstract A new effective catalytic system consisting of [Cp*IrCl2]2/K2CO3 (Cp*=pentamethylcyclopentadienyl) for the N-alkylation of primary amines with alcohols has been developed. As an example, the reaction of aniline with benzyl alcohol in the presence of [Cp*IrCl2]2 (5.0 mol%Ir) and K2CO3 (5.0 mol%) in toluene at 110°C for 17 h gave benzylaniline in an isolated yield of 88%.
Journal of the American Chemical Society | 2009
Ryohei Yamaguchi; Chikako Ikeda; Yoshinori Takahashi; Ken-ichi Fujita
The first homogeneous catalytic system for the efficient reversible dehydrogenation-hydrogenation reactions of nitrogen heterocycles in one flask has been developed using the pyridonate Cp*Ir complex as the single catalyst at relatively low temperature. The reversible catalytic reactions proceed with the reversible interconversion of catalytic species and can be nearly quantitatively repeated five times with almost no loss of efficiency. The remarkable feature of the present homogeneous catalytic system is that the reversible dehydrogenation-hydrogenation reactions proceed with the reversible interconversion of the catalytic species, depending on the absence or presence of hydrogen.
Journal of the American Chemical Society | 2010
Ryoko Kawahara; Ken-ichi Fujita; Ryohei Yamaguchi
Novel water-soluble Cp*Ir-ammine complexes have been synthesized, and a new and highly atom-economical system for the synthesis of organic amines using aqueous ammonia as a nitrogen source has been developed. With a water-soluble and air-stable Cp*Ir-ammine catalyst, [Cp*Ir(NH(3))(3)][I](2), a variety of tertiary and secondary amines were synthesized by the multialkylation of aqueous ammonia with theoretical equivalents of primary and secondary alcohols. The catalyst could be recycled by a facile procedure maintaining high activity. A one-flask synthesis of quinolizidine starting with 1,5,9-nonanetriol was also demonstrated. This new catalytic system would provide a practical and environmentally benign methodology for the synthesis of various organic amines.
Organic Letters | 2011
Ken-ichi Fujita; Tetsuya Yoshida; Yoichiro Imori; Ryohei Yamaguchi
A new catalytic system for the dehydrogenative oxidation of alcohols using a Cp*Ir complex having a functional C,N-chelate ligand has been developed. With this catalytic system, both primary and secondary alcohols were efficiently converted to aldehydes and ketones, respectively. Mechanistic investigations of this catalytic system have revealed that the catalytically active species is a hydrido iridium complex with a functional C,N-chelate ligand.
Journal of the American Chemical Society | 2014
Ken-ichi Fujita; Yui Tanaka; Masato Kobayashi; Ryohei Yamaguchi
Homogeneous perdehydrogenation of saturated bicyclic 2,6-dimethyldecahydro-1,5-naphthyridine and perhydrogenation of aromatic 2,6-dimethyl-1,5-naphthyridine with release and uptake of five molecules of H2 are efficiently achieved by iridium complexes bearing a functional bipyridonate ligand. Successive perhydrogenation and perdehydrogenation of 2,6-dimethyl-1,5-naphthryridine using a single iridium complex also proceed with the reversible interconversion of the catalytic species, depending on the presence or absence of H2.
Organic Letters | 2010
Mingwen Zhu; Ken-ichi Fujita; Ryohei Yamaguchi
A simple and versatile catalytic system for N-alkylation of sulfonamides with various alcohols based on a catalytic hydrogen transfer reaction has been developed under a low catalyst loading of [Cp*IrCl(2)](2) (0.050-1.5 mol %) in the presence of t-BuOK. A variety of N-alkylated sulfonamides were prepared in good to excellent yields. Mechanistic investigations revealed that the key catalytic species in the present system is a sulfonylimido-bridged unsaturated diiridium complex [(Cp*Ir)(2)(mu-NTs)(2)].
Journal of Organometallic Chemistry | 2002
Ken-ichi Fujita; Shigetoyo Furukawa; Ryohei Yamaguchi
Abstract The oxidation of primary and secondary alcohols is carried out in acetone under mild conditions using catalytic amounts of [Cp*IrCl 2 ] 2 and K 2 CO 3 . Primary alcohols are converted into the corresponding aldehydes with high selectivity in good yields. Secondary alcohols are readily oxidized to ketones with smaller amounts of the catalyst.
Tetrahedron Letters | 1983
Ryohei Yamaguchi; Yutaka Nakazono; Mituyosi Kawanisi
Abstract Whereas alkyl Grignard reagents undergo 1,2- and 1,4-additions to N-methoxycarbonylpyridinium chloride in a variable ratio, alkenyl and alkynyl Grignard reagents do the exclusive 1,2-addition to afford 2-substituted N-methoxycarbonyl-1,2-dihydropyridines in fair to excellent yields.
Angewandte Chemie | 2015
Ken-ichi Fujita; Ryoko Kawahara; Takuya Aikawa; Ryohei Yamaguchi
An efficient catalytic system for the production of hydrogen from a methanol-water solution has been developed using a new anionic iridium complex bearing a functional bipyridonate ligand as a catalyst. This system can be operated under mild conditions [weakly basic solution (0.046 mol L(-1) NaOH) below 100 °C] without the use of an additional organic solvent. Long-term continuous hydrogen production from a methanol-water solution catalyzed by the anionic iridium complex was also achieved.