Licamichauxiioic-A and -B acids--two ent-kaurene diterpenoids from Licania michauxii

Bioassay-guided fractionation allowed the isolation of two new cytotoxic ent-kaurene diterpenoids, licamichauxiioic-A and -B acids (1 and 2) from the root extract of Licania michauxii Prance (Chrysobalanaceae). They were characterized as ent-15-oxo-9(11),16-kauradien-19-oic acid (1) and ent-15-oxo-13(14),16-kauradien-19-oic acid (2) by various spectroscopic methods, in particular, 1D and 2D NMR spectra, and chemical evidence.     

Fluoride ion induced reactions of organocilanes with saturated lactones and αβ-enones

Benzyl-, heteroaryl-, and allylsilanes, under the catalytic action of CsF or silica/TBAF, react in mild conditions with electrophiles such as σ-valero and ε-caprolactone, and with cyclohexen-2-one.     

Hydrogen for fluorine exchange in CH4-xFx by monomeric [1,2,4-(Me3C)3C5H2]2CeH: experimental and computational studies

The monomeric metallocenecerium hydride, Cp'(2)CeH (Cp' = 1,2,4-tri-tert-butylcyclopentadienyl), reacts instantaneously with CH(3)F, but slower with CH(2)F(2), to give Cp'(2)CeF and CH(4) in each case, a net H for F exchange reaction. The hydride reacts very slowly with CHF(3), and not at all with CF(4), to give Cp'(2)CeF, H(2), and 1,2,4- and 1,3,5-tri-tert-butylbenzene. The substituted benzenes are postulated to result from trapping of a fluorocarbene fragment derived by alpha-fluoride abstraction from Cp'(2)CeCF(3). The fluoroalkyl, Cp'(2)CeCF(3), is generated by reaction of Cp'(2)CeH and Me(3)SiCF(3) or by reaction of the metallacycle, [(Cp')(Me(3)C)(2)C(5)H(2)C(Me(2))CH(2)]Ce, with CHF(3), and its existence is inferred from the products of decomposition, which are Cp'(2)CeF, the isomeric tri-tert-butylbenzenes and in the case of Me(3)SiCF(3), Me(3)SiH. The fluoroalkyls, Cp'(2)CeCH(2)F and Cp'(2)CeCHF(2), generated from the metallacycle and CH(3)F and CH(2)F(2), respectively, are also inferred by their decomposition products, which are Cp'(2)CeF, CH(2), and CHF, respectively, which are trapped. DFT(B3PW91) calculations have been carried out to examine several reaction paths that involve CH and CF bond activation. The calculations show that the CH activation by Cp(2)CeH proceeds with a low barrier. The carbene ejection and trapping by H(2) is the rate-determining step, and the barrier parallels that found for reaction of H(2) with CH(2), CHF, and CF(2). The barrier of the rate-determining step is raised as the number of fluorines increases, while that of the CH activation path is lowered as the number of fluorines increases, which parallels the acidity.     

Chiral Phosphate in Rhodium‐Catalyzed Asymmetric [2+2+2] Cycloaddition: Ligand,Counterion, or Both?

Investigations based on NMR spectroscopy, mass spectrometry, and DFT calculations shed light on the metallic species generated in the rhodium‐catalyzed asymmetric [2+2+2] cycloaddition reaction between diynes and isocyanates with the chiral phosphate TRIP. The catalytic mixture comprising [{Rh(cod)Cl}₂], 1,4‐diphenylphosphinobutane (dppb), and Ag(S)‐TRIP actually gives rise to two species, both having an effect on the stereoselectivity. One is a rhodium(I) complex in which TRIP is a weakly coordinating counterion, whereas the other is a bimetallic Rh/Ag complex in which TRIP is a strongly coordinating X‐type ligand.     

The Fluorenyl Cation

The fluorenyl cation is a textbook example for a 4π antiaromatic cation. However, contrasting results have been published on how the annelated benzene rings compensate the destabilizing effect of the 4π antiaromatic five‐membered ring in its core. Whereas previous attempts to synthesize this cation in superacidic media resulted in undefined polymeric material only, we herein report that it can be generated and isolated in amorphous water ice at temperatures below 30 K by photolysis of diazofluorene. Under these conditions, the fluorenylidene is protonated by water to give the fluorenyl cation, which could be characterized spectroscopically. Its absorption in the visible‐light range matches that previously obtained by ultrafast absorption spectroscopy, and furthermore, its IR spectrum could be recorded. The IR bands in amorphous ice very nicely match predictions from DFT and DFT/MM calculations, suggesting the absence of strong interactions between the cation and surrounding water molecules.     

A complete experimental approach for synthesis gas separation studies using static gravimetric and column breakthrough experiments

In this work a combination of static gravimetric and inverse chromatographic techniques is used to study the adsorption and separation of the main synthesis gas components, i.e. CO₂, CO, CH₄ and H₂. The single component adsorption isotherms of CO₂, CO, CH₄ and H₂ on faujasite NaX were measured from 303 K to 473 K and over a large range of pressures (from 0 to 1200 kPa). Breakthrough curves of CO₂ and CO and their mixtures were determined at 323 K and 373 K and 100 kPa as an illustrative example. A nice agreement was noticed between the two above-mentioned techniques for single component adsorption. Binary mixture dynamics measurements were compared to the predictions of ideal adsorption solution theory (IAST) via the previously cited single component adsorption data.     

On the possibility of using model potentials for collision integral calculations of interest for planetary atmospheres

The interaction energy in systems (atom–atom, atom–ion and atom–molecule) involving open-shell species, predicted by a phenomenological method, is used for collision integral calculations. The results are compared with those obtained by different authors by using the complete set of quantum mechanical interaction potentials arizing from the electronic configurations of separate partners. A satisfactory agreement is achieved, implying that the effect of deep potential wells, present in some of the chemical potentials, is cancelled by the effect of strong repulsive potentials.     

Untersuchung von Butter, Margarine, Tran und anderen Fetten

Ohne Zusammenfassung     

An Enantiopure Cyclometallated Iridium Complex Displaying Long‐Lived Phosphorescence both in Solution and in the Solid State

A new enantiopure cyclometallated iridium complex bearing a [4]helicenic ‐coordinating and two ‐coordinating dfppy (2‐(2,4‐difluorophenyl)‐pyridyl) ligands was prepared. This complex displayed long‐lived phosphorescence both in solution and in the solid state. Its chiroptical properties, namely electronic circular dichroism and circularly polarized luminescence, were also examined. Comparison with former chiral complexes enabled assignment of the Δ_Ir‐(?) and Λ_Ir‐(+) absolute configurations.     

Inherently Chiral Spider‐Like Oligothiophenes

The racemate of an inherently chiral “spider‐like” octathiophene monomer T8₃ , in which chirality is generated by torsion in its backbone, was synthesized. The racemate was resolved into configurationally stable antipodes by HPLC on a chiral stationary phase. Electrooxidation of the enantiomers resulted in materials displaying high enantiorecognition ability towards the antipodes of some chiral probes. Moreover, the T8₃ racemate demonstrated great aptitude to stimulate formation of 3D rigid architectures if used as a cross‐linking monomer for molecular imprinting. This feature was exploited to devise a molecularly imprinted polymer‐based chemosensor selective for a thymine–adenine oligonucleotide.