Indium-mediated regioselective mono-allylation of 1,5-dicarbonyl compounds and dehydrative cyclization to 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines

An indium-mediated Barbier type mono-allylation of 1,5-dicarbonyl compounds and a subsequent acid-catalyzed dehydrative cyclization afforded 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines.     

Rhodium-catalyzed reductive cyclization of 1,6-enynes and stereoselective synthesis of the putative structure of lucentamycin A and its stereoisomers

A Rh-catalyzed diastereoselective reductive cyclization, mediated by hydrogen, of optically active 1,6-enynes using chiral BINAP was successfully applied to the total synthesis of four stereoisomers of the proposed structure of lucentamycin A. In order to synthesize two of these four stereoisomers, we successfully constructed chiral proline derivatives bearing cis-carbon substituents at C2 and C3 positions based on Krische’s methodology, which has very rarely been reported. Anti-proliferative activities on HCT-116 cell line and NMR data of these four stereoisomers were compared with those of naturally occurring lucentamycine A. The results show that the proposed structure of lucentamycin A needs revision.     

Cross-metathesis of allyl halides with olefins bearing amide and ester groups

An investigation was conducted to determine whether the cross-metathesis (CM) of allyl halides tolerates amide groups. The results show that the ruthenium-based complexes I–III serve as poor catalysts for the CM of allyl halides with olefins that contain an N,N-dimethylamide group. In contrast, the Grubbs–Hoveyda–Blechert second generation catalyst (III) efficiently promotes these processes with olefins bearing a Weinreb amide group. Lastly, a reinvestigation of the ester group tolerance of the allyl halide CM with unsaturated esters demonstrated that III serves as an efficient catalyst for these reactions.     

Effects of solvation on charge distribution of 1,2-semiquinonato/catecholatocobalt complexes containing bis(3-pyridyl) phenylvinylsilane

Recrystallization of [Co(3,5-dbbq)₂(L)₂] (3,5-dbbq?=?3,5-di-tert-butyl-1,2-benzoquinone; L?=?bis(3-pyridyl)phenylvinylsilane) from diethyl ether at ?20?°C produces trans-[Co(3,5-dbbq)₂(L)₂] while the recrystallization from toluene at ?20?°C gives trans-[Co(3,5-dbbq)₂(L)₂]·2PhMe. The complex exists as trans-[Co^III(3,5-dbsq)(3,5-dbcat)(L)₂] (3,5-dbsq?=?3,5-di-tert-butyl-1,2-semiquinonato; 3,5-dbcat?=?3,5-di-tert-butylcatecholato) in the solid state at 173?K. Differences in charge distribution between trans-[Co(3,5-dbbq)₂(L)₂] and trans-[Co(3,5-dbbq)₂(L)₂]·2PhMe have been observed based on the effective magnetic moments and IR spectra of the complexes along with their X-ray crystal structures.     

Photo-crosslinking and negative-type micropattern formation of a polymeric photobase generator containing phthalimido carbamate groups

The photo-crosslinking reaction of a polymeric photobase generator containing phthalimido carbamate (PC) groups was studied and applied to the formation of a negative type micropattern. The copolymer containing PC groups was prepared through the polymerization of methyl methacrylate and phthalimido methacryloxyethylcarbamate (PMC). The photochemical and cross-linking reaction of the copolymer film were studied using the UV and IR absorption spectral changes along with the normalized thickness measurements upon irradiation. The copolymer film was effectively cross-linked upon irradiation with 254 nm UV light, and the cross-linking reaction progressed further with increasing irradiation dose and the amount of PMC units in the copolymer. The photochemical formation of the isocyanato groups was evidenced by comparing the IR absorption spectral changes of the exposed and masked copolymer film. The photo-crosslinking reaction of the copolymer was further studied by using a model compound. The results indicated that the cross-linking reaction occurred because of the formation of urea-type chemical bonds, which were produced through the reaction of the photochemically produced isocyanato and amino groups in the copolymer. A negative micropattern was obtained by using the photo-crosslinking reaction.     

Mizoroki?Heck and Sonogashira Cross‐Couplings Catalyzed by CNC Palladium Pincer Complexes in Organic and Aqueous Media

The catalytic activity of two CNC palladium pincer complexes is evaluated in two fundamental C? C bond‐forming reactions: Mizoroki? Heck and Sonogashira cross‐couplings. After several optimization attempts and a brief comparison with a PCN pincer catalyst, a number of arylated alkenes and diarylethynes are synthesized by procedures based on the catalytic use of the above mentioned CNC Pd pincers in H₂O and DMF.     

Fabrication and Physical Characterization of Biodegradable Poly(butylene succinate)/Carbon Nanofiber Nanocomposite Foams

Nanocomposites of biodegradable poly(butylene succinate) (PBS) and carbon nanofibers (CNFs) were prepared by three different methods, that is, solution blending, melt compounding, and solution and subsequent melt blending (SOAM) method, among which the SOAM method, where nano-scale fillers and polymer matrix are solution-blended and subsequently melt-mixed in a torque rheometer, is a two-step process for obtaining polymer nanocomposite. Dispersion of CNFs in the PBS matrix was characterized by FE-SEM, while thermal and mechanical properties were analyzed by thermogravimetric ananlysis (TGA) and universal test machine (UTM), respectively. The PBS/CNF nanocomposites were then converted to foams by employing a chemical blowing agent (CBA) in the melt. The presence of CNFs increased the melt viscosity of PBS so that the PBS/CNF nanocomposite foams were produced without modifying the chemical structure of the PBS. Nanocomposite foams prepared by the SOAM method showed higher physical properties compared with those prepared by the solution blending and the melt mixing. Cell size and blowing ratio increased with the increase in the CBA content, blowing temperature and time. Cell morphology of the nanocomposite foams was examined by optical microscopy, and the cell size distribution was also investigated.     

Correlated energy disposal and scattering dynamics of the Cl CD4(ν3 = 2) reaction

Molecular chlorine, methane and helium are co-expanded into the extraction region of a Wiley-McLaren time-of-flight spectrometer. After preparing the first overtone of the antisymmetric stretch (ν3 = 2) with direct IR excitation, the reaction is initiated by photolysing Cl2 with 355 nm light to produce mono-energetic Cl atoms with a translational energy of 0.18 eV. The CD3 and DCl products are state-selectively detected via resonance enhanced multiphoton ionization (REMPI) and analysed with the core-extraction technique. Unusual structure in the 3pz CD3 REMPI spectrum suggests the presence of a previously unobserved transition, which we assign to the stretch-bend combination ( [image omitted]) band. The product correlated energy disposal and the scattering distributions are compared with the same quantities for the Cl + CH4(ν3 = 2) reaction and found to be similar, although subtle differences are observed. The results for the Cl + CD4(ν3 = 2) reaction support a localized chemistry model in which the Cl atom interacts with a single C-D oscillator and leaves the CD3 methyl radical as a spectator.     

Raman analyses of co‐phasing and hysteresis behaviors in V2O3 thin film

We present the studies of the phase transition behaviors of V₂O₃ thin film using temperature‐dependent Raman scattering spectroscopy. Our results show that in both the cooling and heating processes of V₂O₃ thin film, the phase transition occurs gradually but not suddenly, contrary to that in single crystal. The coexistence of both the metal and insulator phases with co‐phasing ΔT_c larger than 30 K is observed in both the cooling and heating processes. We discuss that this large co‐phasing ΔT_c should be distinguished with the large hysteresis ΔT_h reported in nanostructures. In addition, our discussions indicate that co‐phasing ΔT_c and hysteresis ΔT_h would be mainly correlated with stress and defect states in sample, respectively. Furthermore, our Raman analyses suggest that stress would also induce phase transitions in V₂O₃, and the stress (pressure)‐induced phase transitions would behave differently comparing with the temperature‐induced transitions under normal pressure. Copyright © 2012 John Wiley & Sons, Ltd.     

Rational development of a selection model for solvent gradients in single-step separation of ginsenosides from Panax ginseng using high-speed counter-current chromatography

A new model of solvent gradients selection was rationally developed for the preparative separation of target compounds. The solvent gradients were selected based on a three-stage screening process where stationary phase retention was ensured by introducing a new parameter termed as the phase ratio. The phase ratio was calculated after mixing the upper phase of a solvent system with the lower phase of a different solvent system (1:1, v/v). The developed model was applied to the one-step separation of eight ginsenosides from Panax ginseng. Three gradients were selected on the basis of new model and eight ginsenosides, Rb(1), Rb(2), Rc, Rd, Re, Rg(1), Rf, and Rh(1), were efficiently separated by high-speed counter-current chromatography coupled with evaporative light scattering detector. The structures of all compounds were characterized by electrospray-ionization mass spectrometry and nuclear magnetic resonance spectroscopy.