Developments of Asymmetric Synthesis Mediated by Chiral Sulfur Reagents

Abstract

Our work on the thio-Claisen rearrangement mediated by an adjacent sulfinyl group is reviewed. The substrates could easily be prepared on a large scale from diacetone-D-glucose. The rearrangement was effected with a diastereoselectivity of 95:5, in favor of the (S,S) or the (R,R) isomer. An approach to natural bis(lactones) was investigated, using a halolactonization reaction and a second [3,3] sigmatropic shift, again mediated by the sulfinyl group. The second part deals with the catalytic enantioselective benzylidenation of aldehydes, mediated by chiral sulfur ylides. We have introduced simple C ₂ symmetric thiolanes for that purpose. The procedure is very practical and enantiomeric excesses up to 96% have been reported for the model of stilbene oxide. A series of ferrocenyl sulfides with planar chirality has also been investigated, leading to unexpected diastereoselectivities and enantiomeric excesses up to 94%.     

1,10‐Phenanthroline and Non‐Symmetrical 1,3,5‐Triazine Dipicolinamide‐Based Ligands For Group Actinide Extraction

The synthesis and evaluation of new extractants for spent nuclear fuel reprocessing are described. New bitopic ligands constituted of phenanthroline and 1,3,5‐triazine cores functionalized by picolinamide groups were designed. Synthetic routes were investigated and optimized to obtain twelve new polyaza‐heterocyclic ligands. In particular, an efficient and versatile methodology was developed to access non‐symmetric 2‐substituted‐4,6‐di(6‐picolin‐2‐yl)‐1,3,5‐triazines from the 1,3,5‐triazapentadiene precursor in the presence of anhydride reagents. Extraction studies showed the ability of both ligand series to extract and separate actinides selectively at different oxidation states (U^VI, Np^V,VI, Am^III, Cm^III, and Pu^IV) from an acidic solution (3 M HNO₃). Phenanthroline‐based ligands show the most promising efficiency for use in the group actinide extraction (GANEX) process due to a higher number of donor nitrogen atoms and a suitable pre‐organization of the dipicolinamide‐1,10‐phenanthroline architecture.     

Asymmetric induction of the iodolactonization reaction of alpha-sulfurated gamma-unsaturated amides

The 1,3-asymmetric iodolactonization reaction of enantiopure alpha-sulfurated gamma-unsaturated amides has been investigated. With sulfinyl and sulfonyl groups, a poorly stereoselective reaction was observed, whereas with a sulfanyl moiety, the diastereoselectivity can be high as 96:4. The role of the oxygen atom on the sulfur moiety is discussed.     

Existence and structure results on almost periodic solutions of difference equations

We study the almost periodic solutions of Euler equations and of some more general Difference Equations. We consider two different notions of almost periodic sequences, and we establish some relations between them. We build suitable sequences spaces and we prove some properties of these spaces. We also prove properties of Nemytskii operators on these spaces. We build a variational approach to establish existence of almost periodic solutions as critical points, We obtain existence theorems fornonautonomous linear equations and for an Euler equation with a concave and coercive Lagrangian. We also use a Fixed Point approach to obtain existence results for quasi-linear Difference Equations.     

Spaces of Quasi-Periodic Functions and Oscillations in Differential Equations

We build spaces of q.p. (quasi-periodic) functions and we establish some of their properties. They are motivated by the Percival approach to q.p. solutions of Hamiltonian systems. The periodic solutions of an adequatez partial differential equation are related to the q.p. solutions of an ordinary differential equation. We use this approach to obtain some regularization theorems of weak q.p. solutions of differential equations. For a large class of differential equations, the first theorem gives a result of density: a particular form of perturbated equations have strong solutions. The second theorem gives a condition which ensures that any essentially bounded weak solution is a strong one.     

Tuning the Guest‐Binding Ability of a Helically Folded Capsule by In Situ Modification of the Aromatic Oligoamide Backbone

Starting from a previously described aromatic oligoamide helically folded capsule that binds tartaric acid with high affinity and diastereoselectivity, we demonstrate the feasibility of the direct in situ modification of the helix backbone, which results in a conformational change that reduces its affinity for guests by two orders of magnitude. Specifically, ring contraction of the central pyridazine unit into a pyrrole in the full helical sequence was investigated by using electrochemical and chemical processes. The sequence containing the pyrrole was synthesized independently in a convergent manner to ascertain its structure. The conformation of the pyrrolic folded capsule was elucidated in the solid state by X‐ray crystallography and in solution by using ¹H and ¹³C NMR spectroscopy. Solution studies revealed an unanticipated solvent‐dependent equilibrium between the anti–anti and syn–syn conformations of the pyrrole ring with respect to its two adjacent pyridine units. Titrations of the pyrrole‐containing sequence monitored by ¹H NMR spectroscopy confirmed the expected drop in affinity for tartaric acid and malic acid that arises from the conformation change in the backbone that follows the replacement of the pyridazine by a pyrrole. The reduction of the pyridazine to a pyrrole was characterized by cyclic voltammetry both on the entire sequence and on a shorter precursor. The lower cathodic potential of the precursor made its preparative‐scale electroreduction possible. Direct in situ modification of the pyridazine within the entire capsule sequence was achieved chemically by using zinc in acetic acid.     

On the Liapunov Second Method for Difference Equations

We study various kinds of stability of a constant solution of an autonomous difference equation by using auxiliary functions like in the Liapunov Second Method. We establish new general principles and we improve several classical results.     

Measure theory and pseudo almost automorphic functions: New developments and applications

In this work, we establish a new concept of weighted pseudo almost automorphic functions using the measure theory. We present new results on weighted ergodic functions like completeness and composition theorems. The theory of this work generalizes the classical results on weighted pseudo almost periodic and automorphic functions. For illustration, we provide some applications for evolution equations which include reaction-diffusion systems and partial functional differential equations.     

First-order necessary conditions for infinite-horizon variational problems

We establish rigorously several pointwise or asymptotic firstorder necessary conditions for infinite-horizon variational problems in general form, in the framework of continuous time. We obtain several new results, and we extend to general differentiable Lagrangians some results known only in special cases. To realize this aim, we justify two different ways to associate a family of finite-horizon problems to an infinite-horizon problem.The authors thank an anonymous referee for providing important historical references     

On the multiplier rules

We establish new results of first-order necessary conditions of optimality for finite-dimensional problems with inequality constraints and for problems with equality and inequality constraints, in the form of John’s theorem and in the form of Karush–Kuhn–Tucker’s theorem. In comparison with existing results, we weaken assumptions of continuity and of differentiability.