Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

First study on the enantioselective palladium-catalyzed C-P cross-coupling reaction between an alkenyltriflate and a phosphine-borane

In this article, we report the first example of a palladium-catalyzed asymmetric C-P cross-coupling reaction between a racemic secondary phosphine-borane, methylphenylphosphine-borane 1, and an achiral triflate. The influence of various parameters such as the structure of the chiral ligand, the temperature and the nature of the solvent on the activity and the selectivity of the reaction is reported. Enantiomeric ratios up to 78:22 were obtained using (S,S)-Me-DUPHOSPdCl₂ as catalyst. A kinetic resolution process is proposed to account for this selectivity.     

Synthesis of 10-deazapteroic and 11-deazahomopteroic acids

The syntheses of 10-deazapteroic and 11-deazahomopteroic acids are described. These compounds along with their simple 6-phenylalkylpteridinol relatives were found to be inactive as antimalarial agents against the Plasmodium berghei or Plasmodium gallinaceum strains. 10-Deazapteroie acid was a potent growth inhibitor of Streptococcus faecium both in the pteridine and tetrahydropteridine forms.     

Dehydrochlorination of alpha-Chlorophosphines, a Simple and General Route to Phosphaalkenes

Primary and secondary alpha-chlorophosphines 2a-g are prepared in ca. 70% yield by chemoselective reduction of the corresponding phosphonic and phosphinic esters with AlHCl(2) and are characterized by (31)P, (13)C, and (1)H NMR and by HMRS. They can be kept several weeks in the refrigerator after purification. They lead then to the corresponding phosphaalkenes 3a-g by HCl elimination. For the volatile alpha-chlorophosphines 2a-e HCl elimination occurs in the gas phase on solid potassium carbonate under VGSR conditions (vacuum gas-solid reactions); the corresponding phosphaalkenes 3a-e are characterized by real time HRMS analysis of the gaseous flow (VGSR/HRMS coupling) and by solid-phase IR spectroscopy after condensation of the gaseous flow on a KBr window cooled to 77 K. The decomposition of phosphaalkenes at this temperature is monitored by IR spectroscopy. The alpha-chlorophosphines 2a-g undergo a HCl elimination in the liquid phase in the presence of a Lewis base; the formation of the transient phosphaalkenes is monitored by (31)P FT-NMR. The temperature of HCl elimination is dependent both upon the P-H acidity of the phosphine precursors and the nature of the base. The (31)P NMR data of the simple phosphaalkenes 3a-g are for the first time reported. They are consistent with the proposed structure. The stereochemistry of the (Z)- and (E)-isomers is established according to the "cis-rule". Phosphaalkenes 3a-g are also characterized by chemical trapping in solution with various dienes, dipoles, or thiols. All of these experiments confirm the transient character of these species. The synthetic potential of this route is evaluated.     

Small exponent asymptotics

We study the surprisingly complicated asymptotic character ofa simple first-order differential equation, which involves aterm with a low exponent of the dependent variable. While numericalsolutions and straightforward asymptotic expansions indicatea clearly defined boundary layer type transition, we find thatthe correct asymptotic structure involves a 'hidden' boundarylayer, and that a straightforward approach cannot discern this.     

Evidence of Phosphonium‐Carbenium Dication Formation in a Superacid: Precursor to Fluorinated Phosphine Oxides

Unambiguously confirmed by low‐temperature in situ NMR experiments, X‐ray diffraction and vibrational spectroscopy, phosphonium‐carbenium superelectrophiles are shown to be generated in strong acidic conditions. Representing crucial intermediates, their exploitation allows for the synthesis of unprecedented fluorinated (cyclic) phosphine oxides.     

Palladium-catalyzed C-P coupling reactions between vinyl triflates and phosphine-boranes: efficient access to vinylphosphine-boranes

Vinylphosphine-borane complexes are easily synthesized by palladium-catalyzed C-P cross-coupling of vinyl triflates with secondary phosphine-boranes. This method allows the synthesis of phosphine derivatives not always easily accessible by other approaches. The vinylphosphine derivatives are purified by chromatography on silica gel. The versatility of the method is proved by using various triflates and diaryl-, dialkyl- and alkylarylphosphine-borane precursors. Chiral enantiopure phosphine-boranes are synthesized from chiral triflates.