Sur la transformation du β-nitrostyrène sous l'action du chlorure d'acétyle en présence d'un chlorure métallique

While β-nitrostyrene yields only hydroxymic or hydroxamic acid derivatives by treatment with acetyl chloride in the presence of zinc, tin, titanium or aluminium chloride, it also gives 3-chloro 2-indolinone and a 5-acetyl derivative of the latter, when the reaction is carried out with ferric chloride. The procedures of this reaction are examined, and a mechanism is suggested.     

Polymétallorotaxanes conjugués contenant des unités pentacoordinantes

Conjugated polymetallorotaxanes containing pentacoordinating units. The present paper reports the synthesis and cyclic voltammetry study of new conjugated polyrotaxanes containing penta-coordinating units around copper or zinc centres. The gathering and threading effect of these metal centres has been used to prepare the desired prerotaxanes, whose macrocyclic and linear components incorporate a tridentate chelate of the terpy type (terpy = 2,2′,6′,2″-terpyridine) and a phen (phen = 1,10-phenantroline) derivative, respectively. Electrochemical oxidative coupling of the end groups (thiophene or pyrrole) leads to the corresponding polymers. Ion-exchange processes, induced by demetalation/remetalation, have been investigated as well as the conductivity of the polymer films prepared.     

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

The behavior of [Zr(CO₃)₄]⁴⁻ complex in solution is studied by determining the coordination mode of the carbonato ligands and the kinetic law of the equilibrium between free and complexed carbonates. Raman polarization and dynamic ¹³C-NMR experiments show that complexed carbonates are bidentate. Magnetization-transfer experiments give the values of pseudo-first-order rate constants for the equilibrium with no net chemical transformation. The treatment of these parameters suggests a second-order rate law. As no solvent effect is noticed, an associative mechanism of ligand exchange is proposed.     

Spectrum Sensing Implemented with Improved Fluctuation-Based Dispersion Entropy and Machine Learning

Spectrum sensing is an important function in radio frequency spectrum management and cognitive radio networks. Spectrum sensing is used by one wireless system (e.g., a secondary user) to detect the presence of a wireless service with higher priority (e.g., a primary user) with which it has to coexist in the radio frequency spectrum. If the wireless signal is detected, the second user system releases the given frequency to maintain the principle of not interfering. This paper proposes a machine learning implementation of spectrum sensing using the entropy measure as a feature vector. In the training phase, the information about the activity of the wireless service with higher priority is gathered, and the model is formed. In the classification phase, the wireless system compares the current sensing report to the created model to calculate the posterior probability and classify the sensing report into either the presence or absence of wireless service with higher priority. This paper proposes the novel application of the Fluctuation Dispersion Entropy (FDE) measure recently introduced in the research community as a feature vector to build the model and implement the classification. An improved implementation of the FDE (IFDE) is used to enhance the robustness to noise. IFDE is further enhanced with an adaptive method (AIFDE) to automatically select the hyper-parameter introduced in IFDE. Then, this paper combines the machine learning approach with the entropy measure approach, which are both recent developments in spectrum sensing research. The approach is compared to similar approaches in literature and the classical energy detection method using a generated radar signal data set with different conditions of SNR(dB) and fading conditions. The results show that the proposed approach is able to outperform the approaches from literature based on other entropy measures or the Energy Detector (ED) in a consistent way across different levels of SNR and fading conditions.     

Synthesis and Properties of First and Second Generation Chiral Dendrimers with Triply Branched Units: A Spectacular Case of Diastereoselectivity

Chiral triols (which may be considered as derivatives of tris(hydroxymethyl)methane), without ( 3-5 ) and with aliphatic ( 6 ) or aromatic ( 7 ) elongating units, and the 1st- and 2nd-generation benzylic branched bromides, 17, 18, 23, 24, 29 , and 30 are subjected to Williamson etherification conditions (NaH in THF). This gave the first ‘fully chiral’ dendrimers, with triple branching and with a stereogenic center at each and every branching point (including the central building block: see 33-42 , 44 , and 46-49 ). Higher than 2nd-generation dendrimers of this type could not be prepared. Certain combinations of diastereoisomeric 2nd-generation branched bromides, 23, 24, 29 , and 30 , and enantiomeric center-piece triols, 3 and 4 , would smoothly react to give the desired dendrimers (e.g., 44 , and 46-49 ) and others would not, with the reactions stopping at the dendritic alcohols containing only two branches (e.g., 45 , and 50-53 ; see Schemes 4 and 5). Considering the distance at which the intermediate diastereoisomeric ‘doubly coupled’ dendritic alcohols differ in their configuration, this diastereodifferentiation or molecular recognition phenomenon (discovered by trying to prepare only 8 out of 2³⁹ possible diastereoisomers!) is a most surprising result. All compounds were fully characterized, and the 2nd-generation dendrimers, e.g., 38 , 40 , and 47 with and without elongation were shown to be monodisperse and without defects, by MALDI-TOF mass spectroscopy (cf. Fig. 4). A simple, unambiguous nomenclature for identification of the novel dendritic compounds is proposed and applied in the Exper. Part.     

Constrained nucleic acids (CNA). Part 2. Synthesis of conformationally restricted dinucleotide units featuring noncanonical alpha/beta/gamma or delta/epsilon/zeta torsion angle combinations

Four dinucleotide building units of nucleic acids in which three out of six backbone torsion angles are included in a dioxaphosphorinane ring structure (D-CNA family) have been synthesized: two diastereoisomeric alpha,beta,gamma-D-CNA {cis and trans} and two diastereoisomeric delta,epsilon,zeta-D-CNA {(S(C4'),R(P)) and (S(C4'),S(P))}. The structural analysis of these conformationally restricted dinucleotides, using NMR spectroscopy and X-ray crystallography, shows that these D-CNA structural elements allow the stabilization of torsion angle combinations, alpha/beta/gamma and delta/epsilon/zeta, that are significantly different from those typically observed in canonical A- or B-form duplexes.     

Experimental study of spinodal decomposition in a 1D conserved order parameter system

We study the zigzag instability coarsening of splay-bend walls formed in a nematic liquid crystal under external fields. The vertexes of zigzag can be considered as kinks in a one-dimensional order parameter system and the geometrical constraints associated with the necessary equal length sum of zig and zag segments impose a conserved quantity in this Cahn-Hilliard-type problem. In the late stage of coarsening, the characteristic length of the system L(t) shows a logarithmic increase in time and the dynamical scaling law holds. We then try to extract the nontrivial asymptotic scaling exponent lambda of the two-time correlation function, defined by lim( approximately [L(t)/L(t('))](-lambda). The scaling exponents with respective time references, t(')=32 and 64 s, after quench are found to be lambda approximately 2 which is larger than the value with respective time reference t(')=0, predicted by numerical simulation.     

Catalytic and asymmetric vinylogous mukaiyama reactions on aliphatic ketones: formal asymmetric synthesis of taurospongin a

Catalytic asymmetric vinylogous Mukaiyama reactions on ketones, leading to the formation of alpha,beta-unsaturated lactones with tertiary alcohols, have been described (11 examples, up to 93% ee). This methodology has been applied in a formal enantioselective synthesis of taurospongin A (12 steps, 6% overall yield).