Hydrofluoroarylation of alkynes with fluoroarenes

A combination of Ni(cod)(2) and PCyp(3) is found to be an effective catalyst for chemoselective activation of the C-H bond of fluoroarenes over C-F bonds followed by insertion of alkynes to allow direct alkenylation of the electron-deficient arenes. The characteristics of the reactions are: a C-H bond ortho to a fluorine substituent is selectively activated; the reactivity of fluorobenzenes is roughly proportional to the number of fluorine atoms. The reaction conditions tolerate a broad range of both alkynes and fluoroarenes containing both electron-withdrawing and -donating groups, thus allowing efficient synthesis of a variety of substituted ethenes containing a fluoroaryl motif in high regio- and stereoselective manners. Mechanistic studies including both labeling experiments and stoichiometric reactions reveal that oxidative addition of C-H bonds in fluoroarenes to nickel(0) is kinetically highly facile whereas that of C-F bonds is thermodynamically favoured.     

On global stability of a nonresident computer virus model

In this paper, we establish new sufficient conditions for the infected equilibrium of a nonresident computer virus model to be globally asymptotically stable. Our results extend two kind of known results in recent literature.     

Studies on cardiotonic agents. II. Synthesis of novel phthalazine and 1,2,3-benzotriazine derivatives

A series of phthalazine and 1,2,3-benzotriazine derivatives which have heterocyclylpiperidino groups was synthesized and tested for cardiotonic activity in anesthetized dogs. Several 6,7-dimethoxyphthalazine derivatives showed relatively potent cardiotonic activity comparable to that of amrinone.     

Spontaneous racemization and epimerization behavior in solution of chiral nitroxides

[reaction: see text] Enantiomerically enriched samples of chiral cyclic nitroxides with a 4-hydroxyphenyl group on the stereogenic center bearing the NO radical group undergo unprecedented spontaneous racemization and/or epimerization in aprotic solvents, which can be well accounted for by the multistep equilibrations involving planar quinoid intermediates.     

Formation of Supramolecular Nanostructures through in Situ Self-Assembly and Post-Assembly Modification of a Biocatalytically Constructed Dipeptide Hydrazide**

Aqueous self-assembly of short peptides has attracted growing attention for the construction of supramolecular materials for various bioapplications. Herein, we describe how the thermolysin-assisted biocatalytic construction of a dipeptide hydrazide from an N-protected amino acid and an amino acid hydrazide leads to the formation of thermally stable supramolecular hydrogels. In addition, we demonstrate the post-assembly modification of the supramolecular architectures constructed in situ tethering hydrazide groups as a chemical handle by means of fluorescence imaging.     

Eu-Doped KCl storage phosphor for erasable and rewritable optical memory utilizing photostimulated luminescence phenomenon

Intense photostimulated luminescence (PSL) with a peak at 420 nm is observed in ultraviolet (UV) Iight-irradiated europium-doped potassium chloride (KCl: Eu) crystalline phosphors. The PSL characteristics of UV-irradiated KCl: Eu phosphor for optical memory application were studied. The excitation and emission mechanisms of the 420 nm PSL, which are consistent with the results obtained, are discussed.     

Stereochemistry-dependent, mechanoresponsive supramolecular host assemblies for fullerenes: a guest-induced enhancement of thixotropy

Self-assembly behaviors of a series of systems (G1, G2, and G3) possessing same organic building blocks based on a substituted anthracene have been investigated in decalin. G2 and G3 are dominated by head-to-tail (ht) and head-to-head (hh) type dimers of G1, respectively. G1 gives a thermoresponsive gel that behaves ideally, showing frequency-independent elastic and viscous moduli. Interestingly, G2 produces a thixotropic gel that shows the signature of structural relaxation, signifying the dynamic nature of the system. In contrast, G3 remains fluidlike. As investigated by scanning electron microscopy (SEM), in the assembly process of G2, first disklike nanoaggregates are formed, and in the second step these aggregates interact to construct the densely packed secondary assembly. A transition from secondary assembly to primary assembly under shear initiates the mechanoresponsive destruction of the gel. In the self-assembly process, G1 propagates in a one-dimensional fashion, whereas G2 and G3 can propagate in a two-dimensionional fashion. The same side orientation of the substituents in G3 facilitates the formation of a compact closed-shell-type structure, which results in the generation of isolated nanocrystals. The long-range weak interaction together with the capability of propagating in two dimensions is found to be essential for the construction of such a mechanoresponsive assembly. C(60) and C(70) could be incorporated successfully in G2 assembly to develop mechanoresponsive fullerene assemblies. The presence of fullerenes not only enhances the elastic properties of G2 but also intensifies the thixotropy. C(70) appears to be a superior guest in terms of property enhancement due to its better size fitting with the concave-shaped host.     

Rhenium-catalyzed insertion of terminal acetylenes into a C-H bond of active methylene compounds

[reaction: see text] A rhenium complex, [ReBr(CO)(3)(thf)](2), catalyzed the intermolecular reactions of 1,3-dicarbonyl compounds with terminal acetylenes and gave the corresponding alkenyl derivatives in excellent yields. These reactions could apply to an intramolecular version and gave the corresponding cyclic compounds quantitatively.     

Synthesis and characterization of titanium and zirconium complexes with silicone-bridged phenoxycyclopentadienyl ligands

Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium dichloride (1a), a useful catalyst precursor for olefin copolymerization, was synthesized at high yield starting from allyl-protected phenolic ligand 3a,which was first treated with 2 equiv. of n-BuLi to selectively give the dilithium salt of 3a along with 1-heptene, a coupling product of a protected allyl ether moiety and butyl anion. Addition of TiCl₄ to the resulting dilithium salt of 3a in toluene afforded 1a in 50% isolated yield. This methodology could be applied to the preparation of related titanium and zirconoium complexes 1b-1d, 8 with silicone-bridged Cp-phenoxy ligands, whereas the reaction starting from methyl-protected precursor 2a did not produce the zirconium complex 8. Copolymerization of ethylene and 1-hexene with the newly prepared complexes was also investigated.     

Nickel-catalyzed arylcyanation of alkynes

A nickel catalyst coordinated by trimethylphosphine is found to effect the addition reaction of Ar-CN bonds in aromatic nitriles across alkynes to give rise to various beta-arylalkenenitriles.