Palladium-catalyzed asymmetric synthesis of 2-pyrrolidinones with a quaternary carbon stereocenter

A palladium-catalyzed asymmetric synthesis of 2-pyrrolidinones with a quaternary stereocenter at the 3-position has been achieved by the reaction of γ-methylidene-δ-valerolactones with alkyl isocyanates. High enantioselectivity has been realized by employing a newly synthesized chiral phosphoramidite ligand.     

An arrayed-window microfluidic device for observation of mixed nanoparticles with an X-ray free-electron laser

Optical Review - A microfluidic device was developed for coherent diffraction imaging using an X-ray free-electron laser (XFEL-CDI). Liquid samples, which are separately packed in reservoirs of the...     

Gate control characteristics in GaAs nanometer-scale Schottky wrap gate structures

Gate control characteristics of GaAs-based quantum wire transistors (QWRTrs) controlled by a nanometer-scale Schottky wrap gate (WPG) are investigated theoretically and experimentally. Gate bias dependence of the effective wire width of fabricated WPG QWRTrs determined theoretically as well as experimentally from Landau plots showed that the nanometer-scale WPG controls the potential very tightly near channel pinch-off and that the pinch-off threshold voltage is strongly dependent on the gate length, L_G, when L_G is shorter than 400 nm. The theory based on the three-dimensional (3D) potential simulation pointed out that Fermi level pinning on the semiconductor surface around the WPGs strongly affects the gate controllability in the nanometer-scale Schottky WPG structure.     

Thermal decomposition and carbonization mechanism of poly-para-phenyleneoxadiazole

Thermal decomposition and carbonization mechanism of poly-para-phenylene-1,3,4-oxadiazole were investigated using FT-IR, thermogravimetry, gas-analysis, XPS, ¹³C-CP/MASFT-NMR, and elemental analysis. At temperatures above 500°C, the decomposition reaction proceeds preferentially on the oxadiazole ring, eliminating p-aminocyanobenzene and p-dicyanobenzene. Formation of carbodiimide compounds and their coupling followed in residual compounds, whose products are important intermediates leading to a planar and polyconjugated nitrogen-containing (e.g., graphite-like) carbon precursor.     

Asymmetric intramolecular [3 + 2] cycloaddition reactions of acylhydrazones/olefins using a chiral zirconium catalyst

Catalytic asymmetric intramolecular [3 + 2] cycloaddition of hydrazone/olefins has been attained. In the presence of a chiral zirconium catalyst prepared from zirconium alkoxide and a BINOL derivative, the desired pyrazolidine derivatives were obtained in high yields with high selectivities. The products were easily converted to 1,3-diamine or beta-aminonitrile derivatives by N-N bond cleavage.     

Stereocontrolled total synthesis of potent immunosuppressant FR901483

A total synthesis of the potent immunosuppressant FR901483 (1) has been accomplished. The key feature of our convergent synthesis is the stereoselective incorporation of the p-methoxybenzyl and methylamino groups within the core moiety 10. Tricycle 10 was itself constructed by an intramolecular aldol reaction of the symmetrical keto-aldehyde 7. [Structure: see text]     

Bismuth triflate-chiral bipyridine complexes as water-compatible chiral Lewis acids

[reaction: see text] Catalytic asymmetric hydroxymethylation of silicon enolates with an aqueous formaldehyde solution has been developed using a chiral bismuth complex. This is the first example of highly enantioselective reactions using a chiral bismuth catalyst in aqueous media. In this paper, we have added Bi(OTf)(3)-1 complex as a "water-compatible Lewis acid". Bi(OTf)3 is unstable in the presence of water but is stabilized by the basic ligand.     

Diverse Synthetic Transformations Using 4-Bromo-3,3,4,4-tetrafluorobut-1-ene and Its Applications in the Preparation of CF2CF2-Containing Sugars,Liquid Crystals,and Light-Emitting Materials

Organic molecules with fluoroalkylene scaffolds, especially a tetrafluoroethylene (CF₂CF₂) moiety, in their molecular structures exhibit unique biological activities, or can be applied to functional materials such as liquid crystals and light-emitting materials. Although several methods for the syntheses of CF₂CF₂-containing organic molecules have been reported to date, they have been limited to methods using explosives and fluorinating agents. Therefore, there is an urgent need to develop simple and efficient approaches to synthesize CF₂CF₂-containing organic molecules from readily available fluorinated substrates using carbon-carbon bond formation reactions. This personal account summarizes the simple and efficient transformation of functional groups at both ends of 4-bromo-3,3,4,4-tetrafluorobut-1-ene and discusses its synthetic applications to biologically active fluorinated sugars and functional materials, such as liquid crystals and light-emitting molecules.     

A family of low-molecular-weight organogelators based on N,N-diacyl-l-lysine: effect of alkyl chains on their organogelation behaviour

A family of low-molecular-weight organogelators based on N^α,N^?-diacyl-l-lysine was synthesized by acylation of N^?-dodecyl-l-lysine with acyl chlorides through the one-pot synthetic procedure and their organogelation properties were examined. These compounds functioned as an organogelator; especially, l-lysine derivatives possessing the branched alkyl groups are a better organogelation property. The NMR and IR studies demonstrate that the organogelation occurred through hydrogen bonding interactions between the amide groups and between the carboxy groups.