Indium(III)-catalyzed intramolecular addition of silyl enolates to alkynes

In the presence of water and a catalytic amount of InBr₃, intramolecular trans-addition of silyl enolates derived from ketones and an aldehyde to alkynes proceeded smoothly to give 4 to 7-membered carbocycles bearing an acyl group. When carboxylic anhydrides were used as electrophiles instead of water, the cyclized products could be functionalized with an additional acyl group.     

Oxygen storage capacity of delafossite-type CuLnO2 (Ln = La, Y) and their stability under oxidative/reductive atomosphere

Delafossite-type CuLnO₂ (Ln = La, Y) was synthesized and investigated their oxygen storage capacity (OSC) under oxidation/reduction cycle. CuLaO₂ was synthesized by heating at 1000 °C for 6 h in N₂ flow and CuYO₂ was synthesized by heating of Cu₂Y₂O₅ at 1190 °C for 1 h in N₂ flow. The oxygen storage capacity values of CuLaO₂ and CuYO₂ at lower temperature were larger than that of CeO₂-based materials which is used as a promoter of an automobile catalyst. The stability of delafossite-type CuLnO₂ under cyclic oxidation/reduction atomosphere was investigated using XRD analysis. During the OSC measurement up to 700 °C, CuLaO₂ decomposed to La₂CuO₄ and Cu₂O. CuYO₂ also partially decomposed to Y₂O₃, Cu₂Y₂O₅ and Cu₂O. These results suggest that oxidative decomposition of CuLnO₂ occurred at high temperature. In lower temperature range, delafossite-type CuLaO_2+x containing excess oxygen existed in both oxidative and reductive atmosphere and it partially decomposed during a hundred of oxidation/reduction cycles.     

Synthesis of pH-responsive polysilane with polyelectrolyte side chains through γ-ray-induced graft polymerization

Polysilanes with polyelectrolyte side chains are synthesized by two methods utilizing γ-ray-induced grafting and the pH responsiveness for one of those polymers is revealed mainly by investigating interfacial behavior of its monolayer at the air/water interface. In the first synthetic method, poly(methyl acrylate) is grafted onto poly(methyl-n-propylsilane) (PMPrS) through γ-ray-induced grafting, and then the PMA chains are hydrolyzed to poly(acrylic acid) resulting in the yield of ca. 97%. Thus PMPrS with polyelectrolyte side chains is successfully synthesized by the graft chain hydrolysis. The other method is the direct grafting of electrolyte monomers. Poly(methacrylic acid)-grafted PMPrS (PMPrS-g-PMAA) can be obtained through γ-ray-induced grafting of methacrylic acid monomers onto PMPrS chains, which shows the effectiveness of radiation grafting for the synthesis of polyelectrolyte graft copolymers. PMPrS-g-PMAA exhibits pH responsive behavior. In addition to the pH-dependence of water solubility, interfacial behavior also depends on the pH. Langmuir monolayers of PMPrS-g-PMAA exhibit different surface pressure-area isotherms according to the grafting yield and the pH of the subphase water. This result suggests that radiation modification is useful for fabricating polysilane-based ordered materials responsive to outer stimuli.     

Evaluation of charge trapping properties of microcrystalline germanium thin films by Kelvin force microscopy

We have prepared highly-crystallized germanium (Ge) films on quartz and evaluated their local charge trapping and electrical conduction properties from topographic and surface potential images simultaneously taken by a conductive atomic force microscopy (AFM) during and after current application to Ge films. By applying a bias of 10 V at which the current of ~ 8 mA flows between the co-planer electrodes on Ge films, the surface potential image which was uniform before bias application shows in-plane inhomogeneity within ~ 1.0 mV commensurate with the surface morphology. Such potential images remained inhomogeneous at zero bias for more than two hours after bias application. The inhomogeneous potential images can be interpreted in terms of the difference in electron concentration in highly-crystallized Ge films presumably caused by electron charging in the grain boundaries, indicating direct detection of electrically separated grain structures and resultant percolation current pass.     

A concise chemical synthesis of a fluorescent βGal-(1,4)-S-βGlc-Cer derivative and its enzymatic elongation by glycosyltransferases

A straightforward chemical synthesis of lyso-lactosylceramide with the terminal galactose linked to glucose through a β-S-glycosidic bond is reported. The product is labeled on the amino-group with tetramethylrhodamine enabling its ultrasensitive detection in capillary electrophoresis using laser-induced fluorescence. The fluorescent product disaccharide is resistant to hydrolysis by glycosidases but is shown to remain as an acceptor substrate for glycosyltransferases for the conversion into the trisaccharides GM3 and Gb3.     

Dialkylaluminum hydride-promoted cyclodimerization of silylated 1,3-enynes via skeletal rearrangement

The dialkylaluminum hydride-promoted reaction of 1-silylalk-3-en-1-ynes gave symmetrical 1,2,3,5-tetrasubstituted benzenes as single regioisomers. The novel cyclodimerization via skeletal rearrangement can be rationalized by an unprecedented mechanism involving sequential hydroalumination, alkene isomerization, carboalumination, carbon-carbon bond cleavage, and retro-hydroalumination.     

Silver-catalyzed coupling reactions of alkyl halides with indenyllithiums

Coupling reactions of tertiary and secondary alkyl halides with indenyllithiums proceeded effectively in the presence of a catalytic amount of silver bromide to provide tertiary- and secondary-alkyl-substituted indene derivatives in good yields.     

Silver‐Catalyzed Benzylation and Allylation of Tertiary Alkyl Bromides with Organozinc Reagents

Silver salts catalyze the benzylation and allylation of tertiary alkyl bromides with organozinc reagents. The reactions create quaternary carbon centers efficiently. Treatment of gem‐dibromoalkanes with benzylic or allylic zinc reagents under silver catalysis leads to dibenzylation or diallylation. The functional‐group compatibility of the present reactions is wider than that of the previous reactions with Grignard reagents.