Olivier Legrand

Enantioselective trimethylsilylcyanation of aromatic aldehydes catalyzed by titanium alkoxide–chiral o-hydroxyarylphosphine oxides complexes

Abstract A series of new chiral titanium alkoxide– o -hydroxyarylphosphine oxides complexes has been used as catalysts in the asymmetric trimethylsilylcyanation of aromatic aldehydes. The corresponding cyanohydrins have been obtained in high chemical yields with good to excellent enantiomeric excesses up to 98%. The influence of the structural features of the catalysts on the enantioselectivity has been investigated.

New chiral o-hydroxyphenyl diazaphospholidine oxide. Catalytic application in asymmetric addition of diethylzinc to aromatic aldehydes

Abstract Synthesis of diastereomerically pure o-hydroxyphenyl diazaphospholidine oxide 2 was achieved from a chiral diamine derived from (S)-proline. This new compound has been tested as catalyst in the asymmetric addition of diethylzinc to aromatic aldehydes. Corresponding sec-alcohols were obtained in high yields (up to 90%) with enantiomeric excesses varying from 15 to >99%. The influence of the solvent and also the important relation existing between the nature of the aldehydes and the enantioselectivity have been investigated.

Chaoticity of a Reverberation Chamber Assessed From the Analysis of Modal Distributions Obtained by FEM

Wave chaos theory is used to study a modeled reverberation chamber (RC). The first 200 modes at a given stirrer position are determined by the finite element method, and the Weyl formula is checked for various RC geometries, from integrable to chaotic. The eigenfrequency spacing distribution varies according to the degree of ray chaos in the RC related to its geometry. The eigenmode distributions are also analyzed and compared to the theoretical Gaussian distribution: close to the lower useable frequency, the modes of the studied chaotic RC fairly respect this asymptotic property. A general result of chaotic systems is illustrated: when perturbed by the stirrer rotation, the resonant frequencies of a chaotic RC avoid crossing. This implies that the frequency sweeps tend to vanish at high frequency.

Complete S matrix in a microwave cavity at room temperature

We experimentally study the widths of resonances in a two-dimensional microwave cavity at room temperature. By developing a model for the coupling antennas, we are able to discriminate their contribution from those of Ohmic losses to the broadening of resonances. Concerning Ohmic losses, we experimentally put to evidence two mechanisms: damping along propagation and absorption at the contour, the latter being responsible for variations of widths from mode to mode due to its dependence on the spatial distribution of the field at the contour. A theory, based on an S -matrix formalism, is given for these variations. It is successfully validated through measurements of several hundreds of resonances in a rectangular cavity.

Scope and Limitations of the Aromatic Anionic [1,3] P–O to P–C Rearrangement in the Synthesis of Chiral o-Hydroxyaryl Diazaphosphonamides

Abstract The influence of numerous parameters in the aromatic anionic [1,3] P–O to P–C rearrangement in the synthesis of chiral o -hydroxyaryl diazaphosphonamides has been envisaged. Various strong bases such as LDA, sec -BuLi, tert -BuLi have been conveniently used. The scope of the regioselectivity of the rearrangement has been particularly studied varying the nature of the phenoxy group implied in this reaction. A totally diastereoselective P–O to P–C migration rearrangement has been observed starting from a thiophosphonamide precursor. Moreover, starting from a phenylthio substituted phosphonamide, a totally diastereoselective P–S to P–C rearrangement of the diazaphosphonamide moiety has also been demonstrated.

Chiral o-hydroxyarylphosphine oxides: a new family of efficient catalysts in asymmetric addition of diethylzinc to benzaldehyde

Abstract A serial of new chiral o-hydroxyarylphosphine oxides has been used as catalysts (5 mol%) in the asymmetric addition of diethylzinc to benzaldehyde. 1-Phenylpropanol is obtained in high chemical yields with good to excellent enantiomeric excesses up to 98%. The influence of the structural features on the enantioselectivity has been investigated.

Experimental width shift distribution: A test of nonorthogonality for local and global perturbations

The change of resonance widths in an open system under a perturbation of its interior has been recently introduced by Fyodorov and Savin [Phys. Rev. Lett. 108, 184101 (2012)] as a sensitive indicator of the nonorthogonality of resonance states. We experimentally study universal statistics of this quantity in weakly open two-dimensional microwave cavities and reverberation chambers realizing scalar and electromagnetic vector fields, respectively. We consider global as well as local perturbations, and also extend the theory to treat the latter case. The influence of the perturbation type on the width shift distribution is more pronounced for many-channel systems. We compare the theory to experimental results for one and two attached antennas and to numerical simulations with higher channel numbers, observing a good agreement in all cases.

Role of the absorption distribution and generalization of exponential reverberation law in chaotic rooms

The theoretical validity of the classical law of reverberation in the true geometrical acoustic limit (TGAL) with mirror reflection relies solely on the conditions that almost all rays are chaotic and that absorption is ‘‘sufficiently weak,’’ as demonstrated by Joyce [J. Acoust. Soc. Am. 58, 643 (1975)]. Recently it was shown that ‘‘sufficiently weak’’ may imply unrealistically large reverberation times [J. Acoust. Soc. Am. 88, 865 (1990)]. Here, this negative result is mitigated by showing that an exponential decay law may still hold in the TGAL for realistic absorptions, depending on the spatial distribution of the absorption within the chaotic room (for instance, in the case of uniform absorption on the walls). The dependence of the sound energy decay on the spatial distribution of absorption stems from the role of special ray trajectories which are analyzed. Also demonstrated theoretically and numerically is that the reverberation time is modified at large absorptions due to fluctuations in the number...

Mechanistic investigation into the addition of diethylzinc to aromatic aldehydes catalyzed by chiral o-hydroxyaryldiazaphosphonamides

Abstract A mechanistic investigation into the addition of diethylzinc to aromatic aldehydes catalyzed by chiral o -hydroxyaryldiazaphosphonamides is described. A positive non-linear effect has been encountered and the X-ray structure of catalyst anti - 1 has been realized.

Selective amplification of scars in a chaotic optical fiber.

In this Letter we propose an original mechanism to select scar modes through coherent gain amplification in a multimode D-shaped fiber. More precisely, we demonstrate the selective amplification of scar modes by positioning a gain region in the vicinity of the self-focal point of the shortest periodic orbit in the transverse motion.