Organocatalytic asymmetric assembly reactions: one-pot synthesis of functionalized beta-amino alcohols from aldehydes,ketones, and azodicarboxylates

[reaction: see text] l-Proline catalyzed the enzyme-like direct asymmetric assembly of aldehydes, ketones, and azodicarboxylic acid esters to provide optically active beta-amino alcohols. This assembly reaction uses both aldehydes and ketones as donors in one pot. The aldol-derived stereocenter is formed with a reduced facial selectivity in reactions involving (R)-amino aldehydes. The reactions can be performed on a multigram scale under operationally simple and safe conditions without the requirement of an inert atmosphere or dry solvents.     

Reduction of sulfoxides with boranes catalyzed by MoO2Cl2

The first example of an organic reduction with boranes catalyzed by a high valent oxo-complex is reported. The systems catecholborane/MoO₂Cl₂(H₂O)₂ (5 mol %) and BH₃·THF/MoO₂Cl₂ (5 mol %) proved to be very efficient for the reduction of sulfoxides to the corresponding sulfides in excellent yields.     

Surface stabilized nanosized Ce(x)Zr(1-x)O(2) solid solutions over SiO(2): characterization by XRD, Raman, and HREM techniques

Ce(x)Zr(1)(-)(x)O(2) solid solutions deposited over silica surface were investigated by X-ray diffraction (XRD), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques in order to understand the role of silica support and the temperature stability of these composite oxides. For the purpose of comparison, an unsupported Ce(x)Zr(1)(-)(x)O(2) was also synthesized and subjected to characterization by various techniques. The Ce(x)Zr(1)(-)(x)O(2)/SiO(2) (CZ/S) (1:1:2 mole ratio based on oxides) was synthesized by depositing Ce(x)Zr(1)(-)(x)O(2) solid solution over a colloidal SiO(2) support by a deposition precipitation method and unsupported Ce(x)Zr(1)(-)(x)O(2) (CZ) (1:1 mole ratio based on oxides) was prepared by a coprecipitation procedure, and the obtained catalysts were subjected to thermal treatments from 773 to 1073 K. The XRD measurements disclose the presence of cubic phases with the composition Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) in CZ samples, while CZ/S samples possess Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), and Ce(0.5)Zr(0.5)O(2) in different proportions. The crystallinity of these phases increased with increasing calcination temperature. The cell a parameter estimations indicate contraction of ceria lattice due to the incorporation of zirconium cations into the CeO(2) unit cell. Raman measurements indicate the presence of oxygen vacancies, lattice defects, and displacement of oxygen ions from their normal lattice positions in both the series of samples. The HREM results reveal, in the case of CZ/S samples, a well-dispersed nanosized Ce-Zr-oxides over the surface of amorphous SiO(2). The structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic geometry and exhibit high thermal stability. Oxygen storage capacity measurements by a thermogravimetric method reveal a substantial enhancement in the oxygen vacancy concentration of CZ/S sample over the unsupported CZ sample.     

Assignment of the relative configuration of spiro[4.5]decanes by 13C, 15N and 17O NMR

The relative configuration of 11 1,4-diazaspiro[4.5]decanes (1a-1j and 1m), 15 1,4-oxazaspiro[4.5]decanes (2a-2o) and 10 1,4-dioxaspiro[4.5]decanes (3a-3n) substituted at the 2-, 6-, 7- or 8-position by a methyl group or using the tert-butyl group as a model for the ananchomeric structure is reported. The relative stereochemistry was analyzed by 1H, 13C, 15N and 17O NMR and all isomers present were characterized spectroscopically. Compounds with a methyl group in the six-membered ring show a chair conformation preference with the methyl group in the equatorial position. Compounds with one or two nitrogens exhibit a tautomeric equilibrium between the imine-diazolidine forms, as demonstrated by IR and 13C NMR.     

31P NMR spectroscopy as a powerful tool for the determination of enantiomeric excess and absolute configurations of alpha-amino acids

An easy method for the determination of the enantiomeric excess (ee) of mixtures of alpha-amino acids, and also for the elucidation of the absolute configuration of each component of the mixture, is reported. The method is based on the formation of diastereoisomers by reaction of the enantiomerically pure acetylacetonate derivative [Pd(acac-O,O')(P(2)-dach)]ClO(4) (4) [P(2)-dach = (1R,2R)-C(6)H(10)(NHPPh(2))(2)] with d,l-mixtures of alpha-amino acids AaH (Pd:AaH = 1:1 molar ratio, refluxing MeOH). The reaction occurs with protonation of the acac ligand and N,O-coordination of the amino acidate group, giving the corresponding [Pd(Aa-N,O)(P(2)-dach)]ClO(4) complexes l-5 and d-6. The composition of these mixtures of amino acidate complexes was analyzed by integration of the corresponding peaks (four doublets, two for each diastereomer) in their (31)P((1)H) NMR spectra. A series of 14 alpha-amino acids was studied (a, alanine; b, 2-aminobutyric acid; c, valine; d, phenylalanine; e, proline; f, leucine; g, isoleucine; h, norleucine; i, serine; j, threonine; k, methionine; l, aspartic acid; m, glutamine; n, cysteine), and excellent agreement between the expected values of ee and those obtained from integration of the (31)P((1)H) NMR spectra was obtained. Moreover, the position of the signals of each isomer is diagnostic, in such a way that the outer doublets are always due to the l-derivatives 5a-l, while the inner ones are due to the d-derivatives 6a-l, allowing the assignation of absolute configurations to each isomer in the mixture.     

The correlation of the stability constants of 1,3-dicarbonylic monochelates of Iron(III) with the acid dissociation constants of the ligand

The variation of the logrithms of stability constants of iron(III) monochelated compounds with structurally similar 1,3-dicarbonylic compounds has been found to be an essentially linear function of the negative logarithms of the acid ionization constant of the ligands. An analytical correlation which could be useful to predict equilibrium constants of iron(III) chelates has been developed. From spectrophotometric and potentiometric data a quantitative evaluation of the stability of the complex has been carried out. Results have provided information regarding substituent effects on the equilibrium constants.     

Diorganotin(IV) derivatives of substituted benzohydroxamic acids with high antitumor activity

A series of diorganotin(IV) and dichlorotin(IV) derivatives of 4-X-benzohydroxamic acids, [HL(1) (X = Cl) or HL(2) (X = OCH(3))] formulated as [R(2)SnL(2)] (R = Me, Et, nBu, Ph or Cl; L = L(1) or L(2)), along with their corresponding mixed-ligand complexes [R(2)Sn(L(1))(L(2))] have been prepared and characterized by FT-IR, (1)H, (13)C, and (119)Sn NMR spectroscopy, mass spectrometry, elemental analysis, and melting points. In addition, single-crystal X-ray diffraction analyses were carried out for [Me(2)SnL(2)] (L = L(1) or L(2)), which show coordination structures intermediate between distorted octahedra and bicapped tetrahedra. The hydroxamate ligands are asymmetrically coordinated by the oxygen atoms, the carbonyl oxygen atom is further away from the metal center than the other oxygen atom. The complexes are stable monomeric species; most of them are soluble not only in chlorohydrocarbon solvents, but also in alcohols and hydroalcoholic solutions. In polar solvents, the mixed-ligand complexes gradually decompose into the corresponding single-ligand complex couples. The complexes exhibit in vitro antitumor activities (against a series of human tumor cell lines) which, in some cases, are identical to, or even higher than, that of cisplatin. For the dialkyltin complexes, the activity increases with the length of the carbon chain of the alkyl ligand and is higher in the case of the chloro-substituted benzohydroxamato ligand. The [nBu(2)Sn(L(1))(2)] complex displays a high in vivo activity against H22 liver and BGC-823 gastric tumors, and has a relatively low toxicity.     

Synthesis of new colloidal formations during the strengthening of different activated hydrated metallurgical slags

This paper reports on a comparison of experimental researches on the hydration hardening of different types of dumped ferrous slag (DFS) (blast furnace, open hearth, electric steel and converter), non-activated and activated with small (2%) additions of Portland cement or lime. Activation was found to accelerate the strengthening processes in the early stages of hydration resulting from the growth of colloidal sol–gel new formations in a more alkaline environment. Over time, these formations became denser and transformed into stone-like amorphous materials with a uniaxial strength of up to 47.6 MPa at 1 year of age. All these types of slag can, therefore, be used in different applications, for example, like traditional binders, such as Portland cement, to different ceramic goods, new construction materials, etc. But till now the results of this research were used only for the preparing of binder materials for natural soils strengthening as road bases in Russia. Highways whose roadbeds were built with these DFS as binder materials have shown excellent performance indices in different parts of Russia, including Siberia and northern regions.     

The extraordinary ability of guanidinate derivatives to stabilize higher oxidation numbers in dimetal units by modification of redox potentials: structures of Mo(2)(5+) and Mo(2)(6+) compounds

Full characterization of the first homologous series of dimolybdenum paddlewheel compounds having electronic configurations of the types sigma(2)pi(4)delta(x), x = 2, 1, 0, and Mo-Mo bond orders of 4, 3.5, and 3, respectively, has been accomplished with the guanidinate-type ligand hpp (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Essentially quantitative oxidation of Mo(2)(hpp)(4), 1, by CH(2)Cl(2) gives Mo(2)(hpp)(4)Cl, 2. The halide in 2 can be replaced by reaction with TlBF(4) to produce Mo(2)(hpp)(4)(BF(4)), 3. Further oxidation of 2 by AgBF(4) produces Mo(2)(hpp)(4)ClBF(4), 4. The change from bond order 4 (in 1) to 3.5 in Mo(2)(hpp)(4)Cl is accompanied by an increase in the Mo-Mo bond length of 0.061 to 2.1280(4) A. A further increase of 0.044 A in the Mo-Mo distance to 2.172(1) A is observed as the bond order decreases to 3 in 4. At the same time, the Mo-N distances decrease smoothly as the oxidation state of the Mo atoms increases. Electrochemical studies have shown two chemically reversible processes at very negative potentials, E(1)(1/2)= -0.444 V and E(2)(1/2)= -1.271 V versus Ag/AgCl. These correspond to the processes Mo(2)(6+/5+) and Mo(2)(5+/4+), respectively. The latter potential is displaced by over 1.5 V relative to those of the Mo(2)(formamidinate)(4) compounds and the first one has never been observed in such complexes. Thus, in surprising contrast to previously observed behavior of the dimolybdenum unit, when it is surrounded by the very basic guanidinate ligand hpp, there is an extraordinary stabilization of the higher oxidation numbers of the molybdenum atoms.     

Asymptotic stability at infinity of planar vector fields

Let >0 andX be aC ¹ vector field on the plane such that: (i) for allq², Det(DX(q))>0; and (ii) for allp², with p, Trace(D(X(p))<0. IfX has a singularity and ² Trace(DX)dxdy is less than 0 (resp. greater or equal than 0), then the point at infinity of the Riemann sphere ²{} is a repellor (resp. an attractor) ofX.