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Masami Sakamoto

Publications and source records attributed to Masami Sakamoto.

18 recordsLinked to original sources
PubMed2006

Palladium-catalyzed sonogashira and hiyama reactions using phosphine-free hydrazone ligands.

Palladium/copper-catalyzed Sonogashira cross-coupling reaction of aryl halides with a variety of terminal alkynes under amine-free conditions in dimethylformamide (DMF) at 80 degrees C gave internal arylated alkynes using PdCl2(MeCN)2 with phosphine-free hydrazone 2a as a ligand and CuI as the cocatalyst in good yields. We also found PdCl2/hydrazone ligand 1d in PhMe at 80 degrees C was a phosphine-free efficient catalyst system for a Hiyama cross-coupling reaction of aryl bromides with aryl(trialkoxy)silanes in good yields.

Journal Article↗
PubMed2006

Synthesis and optical resolution of aminophosphines with axially chiral C(aryl)-N(amine) bonds for use as ligands in asymmetric catalysis.

N-Aryl indoline-type aminophosphines 1a-c were obtained in good yields by a nucleophilic aromatic substitution (S(N)Ar) reaction followed by silane reduction. Aminophosphine 1d was also prepared from 2,3-difluorobenzaldehyde (4) via dimethylhydrazone. Optical resolution of C(aryl)-N(amine) bond atropisomers was achieved using (S)-(+)-di-mu-chlorobis[2-[(dimethylamino)ethyl]phenyl-C(2),N]dipalladium(II) ((S)-10). The determination of absolute configuration and the investigation of the rotation barrier for C(aryl)-N(amine) bond axial stability of an aminophosphine 1 are described. Finally, the ability of the chiral phosphine ligand 1 is demonstrated in a catalytic asymmetric reaction, such as a palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate (up to 95% ee).

Journal Article↗
PubMed2006

Phosphine-free palladium catalyzed Mizoroki-Heck reaction using hydrazone as a ligand.

Glyoxal bishydrazones 1 and pyridyl-hydrazone 2b were prepared and examined as a ligand for the Mizoroki-Heck cross-coupling reaction of aryl halides and olefin. We found that PdCl2(MeCN)2/hydrazone ligand 1e was a phosphine-free efficient catalyst system for a variety of substrates to produce the Mizoroki-Heck coupling products in good yields.

Journal Article↗
PubMed2005

Synthesis, reaction, and recycle of fluorous palladium catalysts for an asymmetric allylic alkylation without using fluorous solvents.

[Chemical reaction: See text] Chiral fluorous aminophosphine 4c bearing two fluorous ponytails was prepared from (S)-prolinol and applied to palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate (7) with a dialkyl malonate-BSA-LiOAc system with high enantioselectivities (up to 97% ee). Results indicated that the chiral fluorous palladium catalyst from ligand 4c was easily separated from the reaction mixture by simple solid/liquid separation and could be reused up to five times.

Journal Article↗
PubMed2005

Phosphine-free hydrazone-Pd complex as the catalyst precursor for a Suzuki-Miyaura reaction under mild aerobic conditions.

[reaction: see text] Glyoxal bis(N-methyl-N-phenylhydrazone) (1) and its related compounds such as 2-pyridinecarboxaldehyde N-methyl-N-phenylhydrazone (3) were prepared and examined as ligands for the Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids. We found phosphine-free catalysts, such as Pd(OAc)(2)/hydrazone ligand 1 or 3, to be efficient catalysts for a variety of substrates to produce the coupling products in good yields.

Catalysis↗
PubMed2005

Amination of N-aryl prolinol via ring expansion and contraction: application to the chiral ligand for the catalytic asymmetric reaction.

Chiral diaminophosphines 4 were prepared from (S)-prolinol-derived aminophosphine oxide 5 by bromination with ring expansion followed by amination with ring contraction and reduction, using trichlorosilane. In the presence of 4 as a ligand, palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate (11) with a dialkyl malonate-BSA-LiOAc system was successfully carried out with good enantioselectivities (up to 98% ee).

Amination↗
PubMed2004

Development of chiral (S)-prolinol-derived ligands for palladium-catalyzed asymmetric allylic alkylation: effect of a siloxymethyl group on the pyrrolidine backbone.

A series of novel chiral aminophosphine ligands are designed and readily prepared from (S)-prolinol. The reactivity and selectivity in the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with a dimethyl malonate-BSA-LiOAc system using these chiral ligands are evaluated, and the structural elucidation of ligands and palladium complex is also conducted. Moreover, a series of trialkylsilylated chiral aminophosphine ligands are prepared and applied to palladium-catalyzed asymmetric allylic alkylation (up to 98% ee).

Journal Article↗
PubMed2004

Real-time-monitored decrease of trichlorophenol as a dioxin surrogate in flue gas using iron oxide catalyst.

The decrease of trichlorophenol by injecting oxidation catalyst into a municipal solid waste incinerator was monitored in real time. Direct sampling atmospheric pressure chemical ionization (APCI)/ion trap mass spectrometry (ITMS) was used for the real-time monitoring. The oxidation catalyst was iron oxide type, which exponentially reduced trichlorophenol emission. CO emission, however, did not show any correlation with the catalyst injection rate. Simultaneous analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) suggested that real-time monitoring of trichlorophenol as a surrogate of PCDDs/PCDFs, has a potential to timely control the optimum injection rate of PCDD/PCDF suppression catalyst continuously and economically.

Air Pollutants↗
PubMed2003

The basic helix-loop-helix genes Hesr1/Hey1 and Hesr2/Hey2 regulate maintenance of neural precursor cells in the brain.

Neural precursor cells proliferate in the ventricular zone while giving rise to neurons of deep layers first, then those of the superficial layers, and lastly, glial cells in the brain. Thus, it is essential to maintain neural precursor cells until late stages of neural development for generation of a wide variety of cell types. Here, we found that the Hes-related basic helix-loop-helix (bHLH) genes Hesr1/Hey1 and Hesr2/Hey2 are expressed in the ventricular zone, which contains neural precursor cells. Misexpression of Hesr1 and Hesr2 by electroporation in mouse brain at embryonic day 13.5 transiently maintains neural precursor cells and thereby increases late-born neurons, which are located in the superficial layers. In contrast, misexpression of the genes at later stages inhibits neurogenesis and promotes generation of astroglial cells. In transient transfection assay with cultured cells, both Hesr1 and Hesr2 inhibit transcription induced by the neuronal bHLH genes Mash1 and Math3. These results indicate that Hesr1 and Hesr2 negatively regulate neuronal bHLH genes, promote maintenance of neural precursor cells, and increase late-born cell types in the developing brain.

Animals↗
PubMed2003

Regioselective photocycloaddition of pyridine derivatives to electron-rich alkenes.

Irradiation of a benzene solution of 3-cyano-2,6-dimethoxypyridine in the presence of ethyl vinyl ether (EVE) gave 1:1 photoadducts, 3-cyano-5-ethoxy-2,8-dimethoxy-4,5-dihydroazocine, in good yields, whose structure was established by X-ray single-crystal analysis. The photoadduct was produced via cycloaddition between the C3-C4 position of the pyridine derivatives and an alkene chromophore. On the other hand, 3-cyano-2,6-dimethoxy-4-methylpyridine cycloadds to EVE at the C2-C3 position of the pyridine ring upon irradiation. The difference is explained on the basis of the steric effect.

Journal Article↗
PubMed2003

Memory of chirality generated by spontaneous crystallization and asymmetric synthesis using the frozen chirality.

Asymmetric synthesis using frozen chirality generated by spontaneous crystallization was performed. Achiral asymmetrically substituted imide with a tetrahydronaphthyl group on the nitrogen atom crystallized in a chiral fashion, with space group P2(1)2(1)2(1). The molecular chirality generated by spontaneous crystallization was retained in cold THF. The half-life determined on the basis of decreasing optical activity followed by CD spectrometer was 7.8, 33.1, and 150.0 min at -20, -30, -40 degrees C, respectively. The energy barrier (DeltaG()) of racemization was calculated with the temperature dependence of the kinetic constant to be 18.24-18.36 kcal mol(-)(1) at 233-253 K. The memorized frozen chirality was transferred to permanent optically active alcohols by nucleophilic addition with n-buthyllithium.

Journal Article↗
PubMed2003

Defective brain development in mice lacking the Hif-1alpha gene in neural cells.

Hypoxia-inducible factor 1alpha (HIF-1alpha) is essential for vascular development during embryogenesis and pathogenesis. However, little is known about its role in brain development. To investigate the function of HIF-1alpha in the central nervous system, a conditional knockout mouse was made with the Cre/LoxP system with a nestin promoter-driven Cre. Neural cell-specific HIF-1alpha-deficient mice exhibit hydrocephalus accompanied by a reduction in neural cells and an impairment of spatial memory. Apoptosis of neural cells coincided with vascular regression in the telencephalon of mutant embryos, and these embryonic defects were successfully restored by in vivo gene delivery of HIF-1alpha to the embryos. These results showed that expression of HIF-1alpha in neural cells was essential for normal development of the brain and established a mouse model that would be useful for the evaluation of therapeutic strategies for ischemia, including hypoxia-mediated hydrocephalus.

Animals↗
PubMed2002

A novel photochemical reaction of 2-alkoxynicotinates to cage-type photodimers.

Irradiation of a benzene solution of 2-alkoxynicotinic acid alkyl esters gave cage-type photodimers in good yields, the structure of which was established by X-ray single-crystal analysis. The maximum quantum yield was 8.0 x 10(-)(2) when a 5.0 M (almost neat) solution was used. Photolysis of phenyl 2-methoxynicotinate promoted photo-Fries rearrangement to give 1,3- and 1,5-rearranged products. Excimer emission of methyl 2-methoxynicotinate was observed at 77 K.

Journal Article↗