Palladium(0)-catalyzed synthesis of medium-sized heterocycles by using bromoallenes as an allyl dication equivalent

We have developed a highly regio- and stereoselective synthesis of medium-sized heterocycles containing one or two heteroatoms via cyclization of bromoallenes bearing an oxygen, nitrogen, or carbon nucleophilic functionality in the presence of a palladium(0) catalyst and alcohol. In this reaction, bromoallenes act as an allyl dication equivalent, and the intramolecular nucleophilic attack takes place exclusively at the central carbon atom of the allene moiety. Interestingly, bromoallenes having a carbon nucleophile with a five-atom tether afford eight-membered rings with trans-configuration, while those having an oxygen or a nitrogen nucleophile give the corresponding cis-rings selectively. This is the first example that demonstrates the synthesis of medium-sized rings via cyclization of bromoallenes, and this reaction provides a very useful method for a catalytic synthesis of seven- and eight-membered heterocycles without using high dilution conditions.     

Development of novel polymer-type dehydrocondensing reagents comprised of chlorotriazines

A novel immobilized dehydrocondensing reagent comprised of a triazine-type dehydrocondensing reagent itself in a polymerized form was synthesized by copolymerization between tetra(ethylene glycol) bis(dichlorotriazinyl) ether and tris(2-aminoethyl)amine.     

Electro-optic effects of colloidal crystals of polymer-modified silica spheres immobilized with gelator

Electro-optic responses of colloidal crystals consist of poly(maleic anhydride-co-styrene)-modified silica spheres (P(MA-ST)/SiO₂) in acetonitrile and the crystals immobilized with a gelator, N-benzyloxycarbonyl-L-isoleucilaminooctadecane (Z-L-Ile-C-18), are studied by reflected-light intensity measurements and time-resolved reflection spectroscopy. Application of an alternating electric field deforms P(MA-ST)/SiO₂ crystal lattices reversibly. The response waveforms from the crystals are dependent on the frequency and strength of the applied electric field; similar dependencies have been qualitatively observed for the colloidal crystals consisting of polystyrene or silica spheres in aqueous media in our previous studies. Both gelated and ungelated P(MA-ST)/SiO₂ crystals change the reflection intensity, however, the amplitude is larger for the latter. The small response for the gelated P(MA-ST)/SiO₂ crystals is attributed to the higher elastic modulus (G). The G value of the gelated P(MA-ST)/SiO₂ crystals in acetonitrile is estimated from the change in the inter-sphere distance to be 8.0 Pa, which is about 2.3 and 2.4 times larger than that for ungelated P(MA-ST)/SiO₂ crystals in acetonitrile and colloidal silica crystals in aqueous media, respectively.     

Searching ultimate nanometrology for AlOx thickness in magnetic tunnel junction by analytical electron microscopy and X-ray reflectometry.

Practical analyses of the structures of ultrathin multilayers in tunneling magneto resistance (TMR) and Magnetic Random Access Memory (MRAM) devices have been a challenging task because layers are very thin, just 1-2 nm thick. Particularly, the thinness (approximately 1 nm) and chemical properties of the AlOx barrier layer are critical to its magnetic tunneling property. We focused on evaluating the current TEM analytical methods by measuring the thickness and composition of an AlOx layer using several TEM instruments, that is, a round robin test, and cross-checked the thickness results with an X-ray reflectometry (XRR) method. The thickness measured by using HRTEM, HAADF-STEM, and zero-loss images was 1.1 nm, which agreed with the results from the XRR method. On the other hand, TEM-EELS measurements showed 1.8 nm for an oxygen 2D-EELS image and 3.0 nm for an oxygen spatially resolved EELS image, whereas the STEM-EDS line profile showed 2.5 nm in thickness. However, after improving the TEM-EELS measurements by acquiring time-resolved images, the measured thickness of the AlOx layer was improved from 1.8 nm to 1.4 nm for the oxygen 2D-EELS image and from 3.0 nm to 2.0 nm for the spatially resolved EELS image, respectively. Also the observed thickness from the EDS line profile was improved to 1.4 nm after more careful optimization of the experimental parameters. We found that EELS and EDS of one-dimensional line scans or two-dimensional elemental mapping gave a larger AlOx thickness even though much care was taken. The reasons for larger measured values can be found from several factors such as sample drift, beam damage, probe size, beam delocalization, and multiple scattering for the EDS images, and chromatic aberration, diffraction limit due to the aperture, delocalization, alignment between layered direction in samples, and energy dispersion direction in the EELS instrument for EELS images. In the case of STEM-EDS mapping with focused nanoprobes, it is always necessary to reduce beam damage and sample drift while trying to maintain the signal-to-noise (S/N) ratio as high as possible. Also we confirmed that the time-resolved TEM-EELS acquisition technique improves S/N ratios of elemental maps without blurring the images.     

Enantioselective inclusion of amide guests into a chiral N,N′-ditrityl amino amide host to compensate the loss of hydrogen bonds broken by installation of trityl groups

A new crystalline N,N′-ditrityl amino amide host included several amide guests in the host cavity to form inclusion crystals. Although the installation of trityl groups into (S)-2-aminopropanamide broke its inherent hydrogen bonds of amide groups, inclusion of guest amides compensated the loss of hydrogen bonds. X-ray crystallography showed that these inclusion cavities and host–guest interactions such as hydrogen bonds, van der Waals interaction, and CH?O interactions play important roles for highly enantioselective inclusion. The enantiomeric inclusion was 67% ee (S-form) for N-phenyl 2-methylbutanamide, 82% ee (S-form) for N-phenyl 2-chlorobutanamide, and 83% ee (S-form) for N-phenyl 2-bromobutanamide.     

Guidelines proposed for designing organic ferromagnets by using a quantum chemical approach

For predicting the characteristics of organic ferromagnetic substances, we have previously proposed a simple rule for conjugated organic molecules based on molecular orbital coefficients by the simple Hückel??s nonbonding molecular orbital (NBMO) method. In this work, we extended the rule to systems including heteroatoms to become more widely applicable to various magnetic polymers. It was proven that the linkage between molecules having an NBMO conserves the original NBMO levels even for the supermolecule after the linkage. In addition, we have also proposed an index to estimate the amount of possessing ferromagnetic property. The reliability of the rule and index is examined by applying both the density functional theory (DFT) with functional methods, i.e., B3LYP, B3PW91, BLYP, PBEPBE, and PBEP86, and the complete active space SCF (CASSCF) calculations to several model molecules.     

Nickel (o)-catalyzed Cycloaddition of Ethoxyethyne with Carbon Dioxide to 4,5-diethoxy-α-pyrone

Ni(O)-phosphine(L) complexes (L=tri-n-alkylphosphines and bis(diphenylphosphino)butane) catalyzed the cycloaddition of ethoxyethyne and carbon dioxide to afford 4,5-diethoxy-α-pyrone regioselectively.