Shizuaki Murata

Trimethysilyl triflate in organic synthesis

Abstract Trimethylsilyl triflate is a powerful silylating agent for organic compounds and acts as a catalyst which accelerates a variety of nucleophilic reactions in aprotic media. The reactions proceed via one-center, electrophilic coordination of the silyl group to hetero functional groups and exhibit unique selectivities.

Trimethylsilyl trifltate catalyzed aldol-type reaction of enol silyl ethers and acetals or related compounds

Abstract Trimethylsilyl triflate with or without added hindered tertiary amines catalyzes directed condensation of enol trimethylsllyl ethers with acetals, orthoformate, or 2-acetoxytetrahydrofuran or -pyrans to give the corresponding β-alkoxy carbonyl compounds. Reaction of enol silyl ethers and carboxonium triflate ion-pair intermediates occurs via acyclic transition states and exhibits moderate to high erythro selectivity independent of the geometry ( E / Z ) of the enol silyl ethers.

Putting Ammonia into a Chemically Opened Fullerene

We put ammonia into an open-cage fullerene with a 20-membered ring ( 1) as the orifice and examined the properties of the complex using NMR and MALDI-TOF mass spectroscopy. The proton NMR shows a broad resonance corresponding to endohedral NH 3 at delta H = -12.3 ppm relative to TMS. This resonance was seen to narrow when a (14)N decoupling frequency was applied. MALDI spectroscopy confirmed the presence of both 1 ( m/ z = 1172) and 1 + NH 3 ( m/ z = 1189), and integrated intensities of MALDI peak trains and NMR resonances indicate an incorporation fraction of 35-50% under our experimental conditions. NMR observations showed a diminished incorporation fraction after 6 months of storage at -10 degrees C, which indicates that ammonia slowly escapes from the open-cage fullerene.

Methane in an open-cage [60]fullerene.

An endohedral methane complex of a fullerene derivative is first synthesized by insertion of a methane molecule through the opening of an open-cage C(60) derivative. The trapped methane is confirmed by NMR spectroscopy and mass spectrometry. Both methane carbon and protons show remarkable upfield shifts in NMR, characteristic of a chemical species in a fullerene cage. CH(4) protons appear as one equivalent signal in the (1)H NMR spectrum, suggesting that even methane can rotate in a C(60) cage.

DNA hydrogel as a template for synthesis of ultrasmall gold nanoparticles for catalytic applications.

DNA cross-linked hydrogel was used as a matrix for synthesis of gold nanoparticles. DNA possesses a strong affinity to transition metals such as gold, which allows for the concentration of Au precursor inside a hydrogel. Further reduction of HAuCl4 inside DNA hydrogel yields well dispersed, non-aggregated spherical Au nanoparticles of 2-3 nm size. The average size of these Au nanoparticles synthesized in DNA hydrogel is the smallest reported so far for in-gel metal nanoparticles synthesis. DNA hybrid hydrogel containing gold nanoparticles showed high catalytic activity in the hydrogenation reaction of nitrophenol to aminophenol. The proposed soft hybrid material is promising as environmentally friendly and sustainable material for catalytic applications.

Photooxygenative partial ring cleavage of bis(fulleroid): synthesis of a novel fullerene derivative with a 12-membered ring

Abstract Photooxidation of tetrasubstituted bis(fulleroid) derivatives gives novel diketone derivatives with 12-membered rings on the surface of fullerene in high yields.

DNA Compaction by Divalent Cations: Structural Specificity Revealed by the Potentiality of Designed Quaternary Diammonium Salts

DNA interaction with quaternary diammonium dications, R(CH3)2N+(CH2)nN+(CH3)2R, having various intercharge distances, lengths, and branching, and the chemical nature of the hydrophobic substituents were investigated by fluorescent microscopy and circular dichroism (CD) spectroscopy to reveal their structural specificity for binding to DNA. The conformational behavior of DNA was found to be highly sensitive to the structure of the dications with separated charges. The distance between two ammonium groups greatly influences the compaction activity of the dications. To explain this situation, we proposed a model that demonstrates that the charge density of the dication and the geometric fit between DNA phosphates and the ammonium groups in the dications play an important role in providing efficient DNA collapse. Elongation of the alkyl substituents (R) in the diammonium salts from ethyl to hexyl did not generate any significant alterations in the compaction activities, whereas the branching of substituents caused a drastic decrease in their compaction ability. Based on the results of CD spectroscopy, it was found that the ability of the dications to provoke a DNA transition from the B‐form to A‐form was also specific: it depended on their intercharge distances and was independent of the length of alkyl substituents.

Stereoselective formation of tetrahydrofuran and -pyran by benzeneselenenyl triflate

Abstract Cyclization of cis - and trans -2-allylcyclohexanols and cyclohexene-3-yl alcohols with benzene-selenenyl triflate affords corresponding fused tetrahydrofurans and -pyrans.

Cyclization of olefinic alcohol by benzeneselenenyl triflate

Abstract Cyclization of 4-, 5-, and 6-hydroxyalkenes with benzeneselenenyl triflate afforded correspondingtetrahydrofurans and -pyrans.

Condensation of enol silyl ethers with 2-acetoxytetrahydrofuran and -tetrahydropyrans

Abstract Trimethylsilyl trifluoromethanesulfonate catalyzes stereoselective condensation of enol silyl ethers and 2-acetoxytetrahydrofuran or -tetrahydropyran derivatives.