Chemistry of epoxysulfones: straightforward synthesis of versatile chiral building blocks

[reaction: see text] Several chiral building blocks have been obtained easily in large quantities from an epoxysulfone (9) that could be obtained in both enantiomeric forms from accessible starting materials.     

Application of monodentate secondary phosphine oxides,a new class of chiral ligands,in Ir(i)-catalyzed asymmetric imine hydrogenation

Secondary phosphine oxides were prepared from R(1)PCl(2) and R(2)MgBr, followed by hydrolysis. They were obtained in an enantiopure form by preparative chiral HPLC. These new monodentate ligands were tested in the iridium-catalyzed hydrogenation of imines at 25 bar. Enantioselectivities up to 76% were obtained at L/Ir = 2. Addition of pyridine (Pyr/Ir = 1:2) raised the ee to 83%. Using pyridine as an additive allowed reduction of the L/Ir ratio to 1 without reduction of ee. [reaction: see text]     

Mono- versus bidentate ligands in rhodium-catalyzed asymmetric hydrogenation. A comparative rate study

[reaction: see text] Bidentate chiral phosphines are no longer essential for achieving a fast and highly enantioselective hydrogenation of alpha- or beta-dehydroamino acid derivatives. In particular, a readily accessible and stable monodentate phosphoramidite can be highly effective in these asymmetric hydrogenations.     

Photochemical and thermal isomerization processes of a chiral auxiliary based donor-acceptor substituted chiroptical molecular switch: convergent synthesis,improved resolution and switching properties

A new type of chiroptical molecular switch is presented where irradiation employing different wavelengths of light induces a reversible helix inversion of a sterically overcrowded alkene bearing a second chiral entity in the form of a stereogenic center present in a pyrrolidine unit. The additional stereogenic center in the chiral auxiliary group has a distinct influence on the switching selectivity of this system and greatly facilitates the resolution of the different diastereoisomers, which is a considerable improvement compared with previously reported systems. In addition, the pyrrolidine stereogenic center causes small energetic differences between the various states of the switch system resulting in a small but significant directional preference in the helix inversion steps.     

Hypergeometric Functions Associated to Cones of Convex Type in a Euclidean Jordan Algebra

In this paper, we study a family of hypergeometric functions associated to cones of convex type in a Euclidean Jordan algebra. We obtain upper and lower bounds and give information about their singularities. The family under consideration was introduced by Sahi (Invent. Math.110 (1992), 409-418) and it plays an important role in the construction of some small representations.     

Some Results on Stability of Retarded Functional Differential Equations Using Dichotomic Map Techniques

This paper deals with the study of the stability of nonautonomous retarded functional differential equations using the theory of dichotomic maps. After some preliminaries, we prove the theorems on simple and asymptotic stability. Some examples are given to illustrate the application of the method. Main results about asymptotic stability of the equation and of itsnonlinear generalization are established.     

The rate function of hypoelliptic diffusions

Let be a hypoelliptic diffusion operator on a compact manifold M. Given an a priori smooth reference measure λ on M, we can then rewrite L as the sum of a λ-symmetric part L⁰ and a first-order drift part Y. The paper investigates the effect of the drift Y on the Donsker-Varadhan rate function corresponding to the large deviations of the empirical measure of the diffusion. When Y is in the linear span of the first and second-order Lie brackets of the X_i's, we derive an affine bound relating the rate functions associated with L and L⁰. As soon as one point exists where Y is not in the linear span of the first and second-order Lie brackets of the X_i's, we show that such an affine bound is impossible. © 1994 John Wiley & Sons, Inc.     

Classification de certains feuilletages associés à un cusp

We study singularities of foliations given by R. Moussu closely related to a conjecture of R. Thom. We give their analytic classification and prove their topological rigidity.

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Notations , ,F 0 - H 0, III - H ₁,H _p I - H-cusp,H _r -cusp I-3 - H _p I-3, III-2 - -cusp II-1 - _r -cusp III-1     

Determination of 1,4-dioxane impurity levels in Triton X-100 raw material by gas chromatography with mass spectrometric detection

Triton X-100 (octoxynol 9) is a commercially available surfactant used as a solvent detergent in numerous pharmaceutical applications including virus inactivation. A byproduct formed during its synthesis is 1,4-dioxane, the cyclic dimer of ethylene oxide and a possible carcinogen to humans. The United States Pharmacopoeia (USP) contains a labor-intensive 1,4-dioxane test for Triton X-100. The method couples vacuum distillation to extract the 1,4-dioxane from the Triton X-100 matrix followed by gas chromatography (GC) using a packed column with flame-ionization detection. In order to provide a more automated and specific test methodology, a headspace GC-mass spectrometry (MS) method has been developed for this application. Analyte quantitation is accomplished by the method of standard additions. The automated sample preparation, coupled with the specificity inherent in high-efficiency capillary column separations together with single-ion MS detection, results in an assay that is more efficient, accurate, and precise than the USP procedure. Performance characteristics of the headspace GC-MS method are contrasted with those characteristics of the USP methodology.