Steric-switched defluorofunctionalization selectivity: controlled synthesis of monofluoroalkene-masked medium-sized heterocyclic lactams and lactones

The steric-switched ipso-defluoroamination-triggered and ipso-defluorooxylation-triggered cyclization of(trifluoromethyl)alkenes with amino alcohols and diamines are achieved under mild conditions. This regioselective strategy distinguishes the different nucleophilic heteroatom sites in amino alcohols and unsymmetric diamines by the sequential defluorinative functionalization of two C(sp³)–F bonds in a CF₃ group. Various attractive monofluoroalkene-masked medium-sized heterocyclic lactams and lactones are obtained in moderate to excellent yields. Simple derivation of these masked-heterocycles efficiently affords useful skeletons of lactams, lactones, and 1,4-oxazepanes in a single diastereoisomer. Mechanism studies indicate that a unique sequential ipso-/γ-selective defluorinative functionalization pathway is involved in these transformations.     

Regioselective introduction of vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds via radical translocation cascade

Described herein is an efficient protocol for the regioselective introduction of a vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds. The cascade process involves the vinyl radical-mediated 1,5-hydrogen atom transfer(HAT) and remote vinyl migration. During the transformation, inert C–H and C–C bonds are consecutively cleaved under mild conditions.The reaction features good functional group tolerance, broad substrate scope, and high regio-/stereo-selectivity.     

Free amino group-directed C(sp2)–H arylation of α-amino-β-aryl esters by palladium catalysis

Native amino-directed palladium-catalyzed C(sp³)–H activation/functionalization has been developed for modification of α-amino acids and peptides. Herein a palladium(Ⅱ)-catalyzed C(sp²)–H arylation of α-amino-β-aryl esters has been disclosed, using the native amino as the directing group. A variety of chiralα-amino-β-aryl esters can be functionalized to give the corresponding ortho-substituted mono-and diarylated products.     

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.     

Toward the most versatile fluorophore: Direct functionalization of BODIPY dyes via regioselective C–H bond activation

Fluorescent dyes are heavily sought for their potentials applications in bioimaging, sensing, theranostic,and optoelectronic materials. Among them, BODIPY dyes are privileged fluorophores that are now widely used in highly diverse research fields. The increasing success of BODIPY dyes is closely associated with their excellent and tunable photophysical properties due to their rich functionalization chemistry.Recently, growing research efforts have been devoted to the direct functionalization of the BODIPY core,because it allows the facile installation of desired functional groups in a single atom economical step. The challenges of this direct C–H derivation come from the difficulties in finding suitable functionalization agents and proper control of the regioselectivity of the functionalization. The aim of this work is to provide an overview of BODIPY dyes and a summarization of the different synthetic methodologies reported for direct C–H functionalization of the BODIPY framework.     

Catalytic transformation of cellulose and its derived carbohydrates into chemicals involving C–C bond cleavage

The catalytic transformation of cellulose, the major component of abundant and renewable lignocellulosic biomass, into building-block chemicals is a key to establishing sustainable chemical processes. Cellulose is a polymer of glucose and a lot research effort has been devoted to the conversion of cellulose to six-carbon platform compounds such as glucose and glucose derivatives through C–O bond activation. There also exist considerable studies on the catalytic cleavage of C–C bonds in biomass for the production of high-value chemicals, in particular polyols and organic acids such as ethylene glycol and lactic acid. This review article highlights recent advances in the development of new catalytic systems and new strategies for the selective cleavage of C–C bonds in cellulose and its derived carbohydrates under inert, reductive and oxidative atmospheres to produce C1–C5polyols and organic acids. The key factors that influence the catalytic performance will be clarified to provide insights for the design of more efficient catalysts for the transformation of cellulose with precise cleavage of C–C bonds to high-value chemicals. The reaction mechanisms will also be discussed to understand deeply how the selective cleavage of C–C bonds can be achieved in biomass.     

Synthesis of unnatural amino acids through palladium-catalyzed C(sp~3)-H functionalization

Unnatural a-amino acids have been extensively used in the modern drug discovery and protein engineering studies. They have also found applications in the development of chiral molecular catalysts and the total synthesis of diverse natural products. Accordingly the development of cost-effective approaches for the preparation of unnatural a-amino acids has received increasing attentions. Among all the available methods for this purpose, direct C–H functionalization of simple amino acids represents one of the most attractive approaches because it exhibits good atom-economy and step-efficiency. In particular, selective functionalization of either the primary or secondary C(sp~3)–H bonds in the amino acids has been explored to make versatile C–C, C–N, C–O, C–B and C–F bonds to modify the side chain of amino acids and even peptides. The present review surveys the recent advances of synthesis of chiral unnatural a-amino acids and peptides through palladium-catalyzed functionalization of un-activated C(sp~3)–H bonds.     

C（sp3）-H bond functionalization of oximes derivatives via 1,5-hydrogen atom transfer induced by iminyl radical

Oximes derivatives have been vastly used in organic synthesis. In this review, C（sp³）-H bond functionalization of oximes derivatives via iminyl radical induced 1,5-hydrogen atom transfer was discussed. According to the different type of products, this review was divided into three parts:（1） C（sp³）-H bond functionalization for C-C bond formation.（2） C（sp³）-H bond functionalization for C-N bond formation.（3） C（sp³）-H bond functionalization for C-S, C-F b...     

Copper-catalyzed enantioselective cyanation of benzylic C–H bonds via radical relay

正Direct methods that enable stereoselective functionalization of C(sp~3)–H bonds could facilitate efficient preparation of therapeutics and agrochemicals,and shall have a major effect on the discovery and development of new pharmaceuticals.Although the transformations through C(sp~2)–H bond cleavage have been significantly developed in the past decades,the direct C(sp~3)–H functionalization,especially the asymmetric transformation is still a big challenge.Demon-     

High pressure,a protocol to identify the weak dihydrogen bonds:experimental evidence of C–H···H–B interaction

Pressure, as a thermodynamic parameter, provides an appropriate method to detect weak intermolecular interactions. The C–H···H–B dihydrogen bond is so weak that the experimental evidence of this interaction is still limited. A combination of in situ high pressure Raman spectra and angle-dispersive X-ray diffraction(ADXRD) experiments was utilized to explore the dihydrogen bonds in dimethylamine borane(DMAB). Both Raman and ADXRD measurements suggested that the crystal structure of DMAB is stable in the pressure region from 1 atm(1 atm=1.01325×10~5 Pa) to 0.54 GPa. The red shift of CH stretching and CH_3 distortion modes gave strong evidence for the existence of C–H···H–B dihydrogen bonds. Further analysis of Raman spectra and Hirshfeld surface confirmed our proposal. This work provided a deeper understanding of dihydrogen bonds.And we wish that high pressure could be applied to identify other unconfirmed hydrogen or dihydrogen bond.     

Synthesis of Multicomponent Oxide Low-Dimensional Systems on the Surface of Porous Silicon Dioxide Using the Molecular Layering Method

Reflecting the research in the field of the surface chemistry of solids over the last 25-30 years, the results related to the application of the molecular layering method for the synthesis of surface low-dimensional structures of complex composition are presented. The regularities of formation of multicomponent mono-, multilayers on the surface of solid-phase matrices are studied on examples of chemical interactions, by a preset program, of chlorides and oxychlorides of titanium, vanadium, phosphorus, chromium, zinc, and iron with hydroxy and secondary functional groups of porous silicon dioxide. On the basis of chemical-analytical and spectroscopic data, structural schemes of synthesized products are proposed and functional interactions in multicomponent monolayers on the surface are considered. The reactivity of the element chlorides and oxychlorides as a function of the chemical composition of surface functional groups of silica and on synthesis conditions is estimated. In view of the revealed regularities of formation of complex low-dimensional systems on silica surface, prospects of application of the resulting data are considered for elaboration of scientific foundations of the chemical nanotechnology of production of solid-phase materials of various functional use, based on the molecular layering method.     

Rheological and electrical characteristics of carbon black dispersions in apolar dielectric medium

Results of the study of the rheological characteristics, as well as of the electrical resistance and capacity of vaseline oil suspensions of carbon blacks with different degrees of oxidation under the action of shear and vibration are reported. Possible mechanisms of suspension conductivity as a function of the regime of dynamic loading are considered. The reasons for the appearance and displacement of dilatant peaks in vaseline oil suspensions of carbon black are proposed as being dependent on the content of particles of solid phase and the degree of surface oxidation.     

Lipids of the oils of the fruit and leaves ofHoppophaë rhamnoides

The analysis of some lipids of four forms of the common sea buckthorn has shown that they all differ with respect to the composition of the fatty acids of the triacylglycerols of the leaves. One of the forms is characterized by an infringement of the specificity of the composition of the fatty acids in positions 2 of the triacylglycerols of the oils of the seeds and the leaves.     

Porous Phosphates of Trivalent Metals: Problems of Their Synthesis and Application

Abstract

Porous phosphates are compounds with a branched system of pores, such as X-ray amorphous xerogels of metalphosphates and crystalline phosphates of zeolite type. Having generalized extensive experimental data about the conditions of Al-, Fe-, Cr-, Ga-, In-, Y-phosphate hydrogels synthesis we found the influence of a number of factors on the rates of their formation, stability of structures and the porosity character of xerogels. The mechanism of porous structure formation of xerogels of metalphosphates has been proposed. The problems connected with the regulation of porous structure of xerogels have been discussed. The formation of porous crystalline aluminophosphates of zeolite type has been accomplished through a number of stages. The nature of alkyl ammonium bases influences the direction of the crystallization process and the type of the structure. It was noted that the stoppind of crystallization on different stages of synthesis gives the possibility to obtain new molecular sieves. Thermal changes and sorption properties of aluminopnosphates of zeolite type have been studied. During the process of removing organic cations the formation of secondary porosity was established. The effectiveness of applying porous metalphosphates in catalysis and adsorption processes has been showed.     

Development of methods for synthesis of surface-modified fluoropolymer-containing composite materials

The results of studies into development of methods for synthesizing new modified fluoropolymer-containing composite materials were summarized. The issues covered include: new modes and initiation methods of graft polymerization of fluoromonomers onto the surface of items of various nature and dispersity without homopolymer formation; nature of the surface active centers of the modified material and how it affects the kinetics and mechanism of both postradiation graft polymerization of tetrafluoroethylene and the subsequent chemical modification of the graft-polymer; major mechanisms and methods of blocking the terminal radicals of the grafted fluoropolymer layer, including those based on reaction with some perfluoroolefins at their double bond, yielding stable long-lived radicals, which allows controlling the physicochemical properties of composite materials; and new methods of synthesis of selective biocompatible sorbents with specific adsorption properties. Accelerating effect of oxygen on polymerization was analyzed, and the phenomenon of ozone initiation of low-temperature polymerization of tetrafluoroethylene was revealed and examined; a new class of high-performance polymerization initiators, namely, perflouroolefin ozonides, was synthesized; and new methods of initiation of polymerization and copolymerization of fluoromonomers, as well as of some other monomers with their use were developed.     

The current state and development of perspectives of application of synthetic antimicrobial agents

The review presents data regarding the main classes of substances applied in pharmaceutics for long-term control of pathogenic microflora. The problems of application of these substances caused by the resistance of pathogenic microflora to the main classes of the biocides are discussed. Mechanisms of action of antimicrobial agents and possible mechanisms of adaptation of pathogenic microflora to these substances are considered. Guanidine-containing cationic polyelectrolytes with different structures affecting their features, as well as the main stages of their mechanism of action, are described. Comparative information on the range of antimicrobial action of representatives of this class based on the results of studies conducted in different periods of time is presented. Analysis of the literature data demonstrated that branched oligohexamethyleneguanidine hydrochloride is a promising compound for the development of pharmaceutical substance.     

Electro-optics of solutions of biopolymers and their complexes

The review summarizes the results of electric-birefringence studies of the molecular properties of biopolymers and their complexes. The application of alternating electric fields makes it possible to study the kinetics of orientation of DNA, RNA, and polypeptide molecules in diluted solutions. An analysis of molecular-mass dependences of relaxation times of biopolymer molecules in terms of the rotational friction theory is used to determine the equilibrium rigidity of macromolecules characterized by Kuhn segment length A. For DNA molecules in buffer solutions with a low ionic strength, the value of A derived from electro-optical measurements is 114 nm. The high sensitivity of electric birefringence to changes in the secondary and tertiary structures of biopolymers ensures its use for the analysis of sequence curvature in short fragments of DNA and for investigation of transitions between different tertiary structures of RNA. The study of electro-optical birefringence in solutions of complexes of DNA and polypeptides with oppositely charged ions of surfactants makes it possible to gain insight into their conformational properties in organic solvents. The stoichiometric complexes of DNA in chloroform occur in the compact globular state, whereas the conformation of complexes formed by various polypeptides depends on their composition and may vary from rodlike to coiled. Electric birefringence in solutions of biopolymer complexes is associated with the orientation of molecules that is due to the external-field-induced dipole moment that appears as a result of a small displacement of ions along the contour of polyion chains. The time of reaching the induced dipole moment is equal to or greater than the time of orientational relaxation of the complex as a whole.     

Effects of the degree of dispersion and the morphology of zinc powder on the thermodynamics of its interaction with polystyrene in solution and in composite films

The adsorption of block PS on the surface of spherical, round, and flaky particles of highly dispersed Zn powders with dimensions of 3.5–23 μm and the interaction of the polymer with the surface of Zn powders in the composite films are studied by refractometry and isothermal calorimetry. During establishment of adsorption equilibrium, the concentration of PS in the bulk of solution increases, while, near the surface of Zn particles, the concentration of PS decreases, thus indicating the predominance of absorption from solution of the solvent o-xylene. With the use of the thermodynamic cycle, including processes of solution of the polymer and Zn-PS film composite and wetting of the Zn powder, the enthalpies of formation of PS-Zn composites are estimated. The enthalpies of mixing of filled compositions comprise two contributions of opposite signs: In the low-filling region, the negative contribution of adhesion interactions prevails, while in the region of high-filled compositions, a positive structural contribution, which is associated with additional loosening of the glassy packing of PS near the filler surface, plays the decisive role. The contribution of adhesion interaction is largely determined by the dimensions of filler particles, while the structural contribution is controlled by their shape. The experimental evidence suggests that spherical particles possess the highest thermodynamic compatibility with the polymer matrix of the composite material.     

The effect of the diversity of molecules in sets and similarity of sets on the quality of prediction in QSAR studies

We report here: (a) formulas/procedures for calculating the similarity of molecules, considering their chemical structure, size, shape and hydrophilicity (b) a procedure for clusterization of the sets of molecules, according to similarity (c) formulas/procedures for calculating the diversity of molecules in clusterized sets as well as similarity of clusterized sets, based on Shannon Entropy formalism The paper analyses the influence of the diversity of molecules and similarity of calibration/prediction sets on the quality of prediction for prediction set molecules. The calculated influence of certain molecular feature (chemical structure, size, shape and hydrophilicity) on toxicity depends on the structure of the database, specifically the number of molecules and diversity of molecules having analyzed molecular feature. A QSAR analysis of 49 phenol derivatives revealed the effect of the diversity of molecules in sets and of the similarity of sets on the quality of prediction for prediction set molecules: (a) a direct correlation with the similarity of sets, regardless of analyzed molecular feature (b) an inverse correlation with the diversity of molecules in the calibration set, from the point of view of chemical structure, size and shape (c) a direct correlation with the diversity of molecules in calibration set, from the point of view of hydrophilicity (d) a direct correlation with the diversity of molecules in prediction set, regardless of analyzed feature.     

Quantitative X-ray fluorescence analysis of multielemental subjects of complex shape without implementation of reference standards

A theoretical dependence of the ratio of intensities of X-ray fluorescence lines of chemical elements on the ratio of their concentration in a sample is suggested. The effect of various experimental factors on parameters of the obtained model is considered. A method of quantitative X-ray fluorescence analysis of multielemental subjects using the suggested calibration dependence without the implementation of reference standards is described. The adequacy and analytical advantages of the developed approach are demonstrated for the determination of the elemental composition of a sample of a metal alloy of complex shape.