Structural study of methyl 2,6-diphenyl-N-methyl-4-oxopiperidine-3,5-dicarboxylate enolic forms

The methyl 2,6-diphenyl-1-methyl-4-oxopiperidine-3,5-dicarboxylates 1 were synthesized by the Mannich procedure from methyl 3-oxoglutarate, benzaldehyde and methylamine. Keto-enol tautomerism as well as configurational isomerism at C-2 were observed. The stereochemistry of the Ib and Ic enolic forms were determined by ¹H and ¹³C nmr data.     

Determination of propazine by differential pulse polarography in micellar and emulsified media

An electroanalytical study of the herbicide propazine's reduction process in micellar solutions and oil-in-water emulsions is reported. The anionic surfactant sodium pentanesulphonate was chosen as the most suitable. The differential pulse polarograms of micellar solutions had two reduction peaks below pH 2.0, whereas only one peak was obtained above pH 2.O. Ethyl acetate was chosen as the organic solvent to form propazine emulsions. Unlike in micellar solutions, the DPP polarograms of propazine emulsions showed only one peak even at pH < 2.0, suggesting that propazine hydrolysis was hindered in the emulsified medium. The limiting current is diffusion-controlled and the electrode process is irreversible. Propazine can be determined by differential pulse polarography over the 1.0 × 10^–1 – 1.0 × 10^–1moll^–1 and 1.0 × 10^–15 – 4.0 × 10^–1 moll^–1 concentration ranges and the limit of detection was 2.8 × 10^–1 moll^–1. Of the potential interferents simazine, methoprotryne and terbutryn (alls-triazines), thiram (a dithiocarbamate), dinoseb (nitrophenolic), and heptachlor (chlorinated cyclo-diene herbicide), only the first two were significant (10% error for equimolar concentrations). The method was applied to the determination of propazine in spiked drinking water. At a concentration level of 2.0 × 10^–1 moll^–1 a recovery of 94 ± 6% was obtained, after tenfold concentration on Sep-Pak.     

Thermal Behaviour of some dioxane adducts ofM(C6F5)2 (M=Pd,Pt)

The thermal treatment of the pentafluorophenyl derivativesM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) or Pt (n=2); Dx=dioxane] leads to the formation of the new dioxane adducts M(C₆F₅)₂Dx (M=Pd, Pt) and Pt(C₆F₅)₂Dx_1.5. Calculations of the order of reaction and the activation energy of some of the decomposition reactions are described. The values were determined by the Coats-Redfern and Freeman-Carroll methods. Structural data on the isolated intermediates were obtained by infrared spectroscopy and magnetic susceptibility measurements.

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Zusammenfassung Die thermische Behandlung der PentafluorphenylderivateM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) oder Pt (n=2); Dx=Dioxan] führt zu der Bildung der neuen DioxanaddukteM(C₆F₅)₂Dx (M=Pd, Pt) und Pt(C₆F₅)₂Dx_1.5. Die Berechnungen der Reaktionsordnung und der Aktivierungsenergie einiger Zersetzungsreaktionen werden beschrieben. Die Werte wurden durch die Methoden von Coats-Redfern und Freeman-Carroll bestimmt. Die Strukturangaben der isolierten Zwischenprodukte wurden durch Infrarotspektroskopie und Messung der magnetischen Suszeptibilität erhalten.

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(₆F₅)₂, M=Pd n=2, 3 Pt _n=2, - , -M(C₆F₅)₂ (=Pd, Pt) (₆F₅)_21,5. , — —. .

     

An effective enantioselective approach to the securinega alkaloids: total synthesis of (-)-norsecurinine

[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield.     

Synthesis, 1H, 13C-NMR and mass spectral study of aryloxyquinuclidinium salts

A series of 3 -aryl -3 -hydroxy-N -(4 ′-aryloxobutyl)quinuclidinium salts have been synthesized. The ¹H nmr, ¹³C nmr and mass spectra of these compounds are described and discussed.     

Hexacyanocobaltate(III) anions as precursors of Co(II)-Ni(II) cyano-bridged multidimensional assemblies: hydrothermal syntheses, crystal and powder X-ray structures, and magnetic properties

Three novel cyanide-bridged heterobimetallic coordination polymers have been synthesized by hydrothermal routes, in superheated water solutions, by using K3[Co(CN)6], NiCl2.6H2O, and alpha-diimine ligands: [Ni(CN)4Co(phen)] (1; phen = 1,10-phenanthroline), [Ni(CN)4Co(2,2'-bipy)] (2; 2,2'-bipy = 2,2'-bipyiridine), and [Ni(CN)4Co(2,2'-bipy)2] (3). The isostructural compounds 1 and 2 contain a two-dimensional network with Co(II) centers octahedrally coordinated by one chelating 2,2'-bipy ligand and four cyanide groups of four distinct [Ni(CN)4]2-, through crystallographically equivalent, bridging units. Compound 3 contains one-dimensional zigzag chains in which the Co(II) ion is coordinated by two chelating 2,2'-bipy ligands and two cyanides from two different [Ni(CN)4]2- units cis to each other. These compounds have been fully characterized by single-crystal or unconventional powder X-ray diffraction analyses and variable-temperature magnetic measurements.     

Highly diastereoselective cyanation of methyl ketimines obtained from (R)-glyceraldehyde

[reaction: see text] Addition of trimethylsilyl cyanide to ketimines derived from (R)-2,2-dimethyl-1,3-dioxolan-4-yl methyl ketone to generate a quaternary stereocenter has been achieved with high yields and excellent diastereoselectivity. The stereoselectivity was found to be temperature and solvent dependent. The beta-hydroxy-alpha-amino nitrile of syn configuration was the major compound in kinetically controlled reactions, whereas the anti stereoisomer was obtained in excess in thermodynamically controlled reactions. Double stereodifferentiation under kinetic control conditions was successful, and the cyanation reaction occurred with complete syn diastereoselectivity using the matched pair. The versatility of the resulting amino nitrile as a synthetic intermediate was tested by performing the synthesis of orthogonally protected (R)-(2-aminomethyl)alanine.     

Synthesis of isomeric β-haloethylthienopyrroles

The preparation of ethyl 4-(2-bromoethyl)thieno[2,3-b]pyrrole-5-carboxylate and ethyl 6-(2-bromoethyl)thieno[3,2-b]pyrrole-5-carboxylate by reaction of t-butyl 2-(2-thienyl)carbazate and t-butyl 2-(3-thienyl)carbazate with ethyl-5-bromo-2-oxopentanoate are described.     

Crystal and Molecular Structure of (BzlMe3N) 2 + [Fe2OCl6]2-

The crystal and molecular structure of (BzlMe₃N) ₂ ⁺ [Fe₂OCl₆]^2- has been determined. The asymmetric unit contains two benzyltrimethylammonium cations and two half -oxo-bis(trichloro-iron(III)) anions. The bridging -oxygen atoms of these anions are located over crystallographic symmetry elements. Therefore, the two anions resulting from the symmetry operations correspond to two different conformers presenting angular and linear dispositions of the Fe-O-Fe bond angle. Mössbauer spectrum consists of two asymmetric lines that are adequately simulated by two equally populated quadrupole doublets associated with the two iron sites.