Total synthesis of amaryllidaceae alkaloid buflavine

A concise synthesis of the amaryllidaceae alkaloid buflavine (1) and its regioisomer (2) involving sequential Meyers' biaryl coupling, enecarbamate formation, and hydrogenation followed by ultimate intramolecular reductive amination is presented.     

Regioselective palladium-catalyzed phenylation of ethyl 4-oxazolecarboxylate

The efficient and regioselective palladium-catalyzed C-2 arylation of ethyl 4-oxazolecarboxylate 1 with phenyliodide is described. The different parameters (solvent, base, ligand and catalyst) for the optimal conditions of this arylation process have been screened.     

Chemoenzymatic synthesis of highly enantiomerically enriched secondary alcohols with a thiazolic core

Stereoselective preparative enzymatic acylation and hydrolysis/methanolysis of various C-substituted rac-thiazol-2-yl-methanols were achieved for the preparation of enantiopure or enantiomerically enriched, naturally occurring 2-hydroxymethylthiazoles. The absolute configurations of the resulting secondary alcohols were determined by a detailed ¹H NMR study of Mosher’s derivatives.     

Amine-Directed Palladium-Catalyzed C−H Halogenation of Phenylalanine Derivatives

An efficient primary-amine-directed, palladium-catalyzed C−H halogenation (X=I, Br, Cl) of phenylalanine derivatives is reported on a range of quaternary amino acid (AA) derivatives thanks to suitable conditions employing trifluoroacetic acid as additive. The extension of this original native functionality-directed ortho-selective halogenation was even demonstrated with the more challenging native phenylalanine as tertiary AA.     

A mild anionic method for generating o-quinone methides: facile preparations of ortho-functionalized phenols

A low-temperature method for generating o-quinone methides is described which permits facile introduction of assorted R substituents onto the aryl ring system at low temperature. The method is useful for the efficient preparation of ortho-ring-alkylated phenols.     

Determination of the electrical properties of 2.5 nm thick silicon-based dielectric films: thermally grown SiOx

Ultra-thin (<5 nm thick) thermal oxide and oxynitride films with different compositions are candidates for complementary metal/oxide/semiconductor technology in ultra-large-scale integration (ULSI) applications. The latter are expected to offer the best compromise between nitrides and oxides. The aim of this work is to measure the electrical properties of a leaky 2.5 nm thick thermally grown oxide film using the high frequency capacitance–voltage (HF C(V)) measurements. The cleanliness and the surface roughness of the Si(1 0 0) surface were measured prior to in situ oxidation by means of, respectively, Auger electron spectroscopy (AES) and atomic force microscopy (AFM). The physical–chemical properties of the thermal oxide film were measured by AES (film thickness, composition), Fourier transform infrared spectroscopy (FTIR) (composition, vibration modes), cross-sectional transmission electron microscopy (TEM) (film thickness, homogeneity) and electron energy loss spectroscopy (EELS) (gap width determination). The results are compared to those obtained for the native oxide film and a chemical oxide film. The latter was first grown on the silicon substrate to prevent contamination and surface disorder after flash heating in vacuum prior to oxide growth. The substrate Si(1 0 0) surface cleaned in ultra-high vacuum (UHV) was then oxidized in a 10⁻³ mbar oxygen (O₂) gas pressure at 900°C to get the 2.5 nm thick oxide film. The grafting of a self-assembled insulating monolayer (SAM) of organic molecules on the grown oxide film permits us to obtain analysable capacitance as a function of voltage data. Indeed, this monolayer made up of octadecyltrichlorosilane molecules leads to a reduction of the leakage current through the aluminium/self-assembled monolayer/oxide/silicon heterostructure. The resulting current as a function of voltage data were compared to those of a standard 2.5 nm thick oxide film. The method proposed here to extract the electrical parameters of the thermal oxide film is demonstrated to be valid. We show mainly that the reduction of the leakage current through the aluminium/self-assembled monolayer/thermal oxide/silicon heterostructure is seven orders of magnitude bigger than in the case of the native oxide film.     

A concise total synthesis of the azaphenanthrene alkaloid eupolauramine.

A six-step total synthesis of the azaphenanthrene alkaloid eupolauramine 1 has been achieved using combinational metalation-cyclization tactics. The synthetic route involved first the construction of the azaisoindolinone 9 by aryne-mediated cyclization of he phosphorylated pyridocarboxamide 7 and subsequent dephosphorylation. Metalation of 9 followed by connection of the hydroxybenzyl appendage and E(1)CB anti-elimination allowed the formation of the halogenoarylmethylene azaisoindolinone 4 in the exclusive E-form. Oxidative radical cyclization gave rise to the azaphenanthrene skeleton and regioselective bromination of 3 induced the incorporation of the bromine atom at the 6-position of the azaphenanthrene lactam. Ultimate replacement of the bromine atom of 2 by the methoxy functionality by sequential transmetalation, in situ oxidation, and O-methylation of the phenolic derivative 14 completed the synthesis of the target natural product eupolauramine.     

Direct Numerical Simulation of the Three-Dimensional Transition to Turbulence in the Incompressible Flow around a Wing

The onset of the secondary instability and the successive steps ofthe 3D transition to turbulence are examined in the flow around a wing of NACA0012 section, constant along the spanwise direction. The wing is placed in a uniform flow upstream, at 20° of incidence and at the Reynolds number of 800. The spanwise length is equal to four chords. The objectives of this study are the identification of the three-dimensional transition mechanism and the development of the early stages of turbulence in the present class of unsteady aerodynamic flows. A detailed processing of the DNS signals carried out by an appropriate conditional sampling allows the identification of the physical mechanisms related to the birth of turbulence and to the non-linear interaction with the 3D coherent structures in the near region.     

Etude variationnelle d'une double perturbation. Application au calcul des constantes de couplage entre spins nucleaires

The calculation of molecular electronic polarizability tensor components is presented in the CNDO approximation using several methods, on one hand a perturbation calculation, on the other hand a variational method. Results obtained on thirty molecules are used to compare these methods and to discuss their usefulness.