Stereoselective Barbier-type allylation reaction of trifluoromethyl aldimines

Trifluoromethyl aldimines could react, under Barbier conditions in the presence of activated zinc, in DMF at room temperature or in THF at reflux, with various allyl bromides to provide the corresponding homoallylamines. Secondary homoallyl trifluoromethylamines were stereoselectively obtained from the optically active aldimine 12 with an excellent diastereoisomeric excess (98%).     

Hydrogen adsorption in the nanoporous metal-benzenedicarboxylate M(OH)(O2C-C6H4-CO2) (M = Al3+, Cr3+), MIL-53

Hydrogen adsorption has been studied in the nanoporous metal-benzenedicarboxylate M(OH)(O2C-C6H4-CO2) (M = Al3+, Cr3+); these solids show a hydrogen storage capacity of 3.8 and 3.1 wt.% respectively when loaded at 77 K under 1.6 MPa.     

Asymptotique des approximants de Hermite–Padé quadratiques de la fonction exponentielle et problèmes de Riemann–Hilbert

We describe the asymptotic behavior of the polynomials $\text{p,}\text{q,}\text{r}$ of degree n in type I Hermite–Padé approximation to the exponential function, i.e., $\text{p(z)}\text{e}{}^{\mathrm{?z}}\text{+q(z)+r(z)}\text{e}{}^{\mathrm{z}}\text{=}\text{O}\text{(z}{}^{\mathrm{3n+2}}\text{)}$ as z→0. A steepest descent method for Riemann–Hilbert problems, due to Deift and Zhou, is used to obtain strong uniform asymptotics for the scaled polynomials $\text{p(3nz),}\text{q(3nz),}\text{r(3nz)}$ in every domain of the complex plane. An important role is played by a three-sheeted Riemann surface and certain measures and functions defined on it. To cite this article: A. Kuijlaars et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Collisional narrowing and spectral shift in coherent anti-stokes Raman spectra of molecular nitrogen up to 2500 bar and 700 K

CARS spectra of the N₂ Q-branch up to 2500 bar and 700 K have been measured. Calculated spectra based on theoretical models show significant disagreement with measured spectra above 300 bar so that CARS temperature measurements are in error by 130 K at 700 K and –150 K at 295 K. The spectral shift of the Q-branch reaches an asymptotic value corresponding to that measured in liquid nitrogen.     

Structure and biosynthesis of the ergot pigments

In addition to the well known alkaloids, ergot contains two groups of yellow to red pigments, between which there is a close and novel biogenetic relation. The pigments are anthraquinonecarboxylic acids and dimeric hydroxanthone derivatives (ergochromes), the structures of which, including the absolute configurations at 80 centers of chirality, have been completely determined. The intermediates involved in the biosynthesis have been largely established by feeding with labeled precursors, and its course by model experiments.