Solution- and solid-phase synthesis of 4-hydroxy-4,5-dihydroisoxazole derivatives from enantiomerically pure N-tosyl-2,3-aziridine alcohols

[reaction: see text] Enantiomerically pure N-tosyl-2,3-aziridine alcohols are directly converted into 4-hydroxy-4,5-dihydroisoxazole 2-oxides through oxidation to the corresponding aldehydes followed by in situ tandem nitroaldol-intramolecular cyclization. This study was concerned with (i) the selection of a suitable aziridine activation, (ii) the preparation of the target 4-hydroxy-4,5-dihydroisoxazole derivatives in solution, and (iii) the elaboration of a solid-phase process using hydroxy Merrifield-supported nitroacetic acid ester.     

Crystal Growth and Structural Refinements of the Y2SiO5, Y2Si2O7 and LaBSiO5 Single Crystals

The laser crystals of chromium doped yttrium oxyorthosilicate (YSO) were grown from the melt by Czochralski technique. The crystals of YSO, yttrium pyrosilicate and stillwellite-like lanthanum borosilicate were obtained from high temperature solutions. Lithium and potassium di- and trimolybdates were used as fluxes in the growth experiments on silicate crystals. In the case of borosilicate crystals, the choice of fluxes was based on the potassium trimolybdate with an excess of potassium fluoride. The composition of grown crystals was studied by electron microprobe analysis, and structural characteristics were determined for all the single crystals.     

A successful sample system for sulfur plant chromatographic analysis

Summary A successful sample system for sulfur plant chromatographic analysis is described.

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Zusammenfassung Für die technische gaschromatographische Schwefelbestimmung wird ein Probenahmesystem beschrieben, mit dem befriedigende Ergebnisse erzielt werden konnten.

     

Surface states and negative electron affinity in polyethylene

First-principles calculations are used to investigate the electronic properties of the surfaces of polyethylene. The calculations support the experimental evidence of a negative electron affinity, with calculated values of -0.17 eV and -0.10 eV for surfaces with chains perpendicular and parallel to the surface normal, respectively. Both surfaces exhibit a surface state with binding energy -1.2 +/- 0.5 eV with respect to the bulk polyethylene conduction band minimum. Implications of these findings on spectroscopy, as well as on the transport and aging properties of polyethylene for high-voltage applications, are discussed.     

Lewis acid-mediated azidolysis of 2,3-three membered heterocyclic amines

The Lewis acid-catalyzed regioselective azidolysis of 2,3-three membered heterocyclic amines has been investigated. The results obtained demonstrated that using TMSN₃ as a source of azide, the appropriate choice of Lewis acid allowed to obtain different regio- and stereocontrolled precursors of aminoalcoholic and triaminic sequences. Considering the occurrence of these moieties in the structure of many biologically active compounds, the present methodologies could represent a powerful tool in organic synthesis for the preparation of interesting molecules.     

Improved Procedure for the Reduction of Esters to Alcohols by Sodium Borohydride

An improved procedure for the employment of NaBH₄ in the reduction of ester function is described.     

Self-trapping vs. non-trapping of electrons and holes in organic insulators: polyethylene

We show, by electronic structure based molecular dynamics simulations, that an extra electron injected in crystalline polyethylene should fall spontaneously into a self-trapped state, a shallow donor with a large novel distortion pattern involving a pair of trans-gauche defects. Parallel calculations show instead that a hole will remain free and delocalized. We trace the difference of behavior to the intrachain nature of the hole, as opposed to the interchain one of the electron, and argue that applicability of this concept could be more general. Thus electrons (but not holes) should tend to self-trap in saturated organic insulators, but not for example in aromatic insulators, where both carriers are intrachain.     

Direct, one-pot reductive alkylation of anilines with functionalized acetals mediated by triethylsilane and TFA. Straightforward route for unsymmetrically substituted ethylenediamine

A new, robust, and reliable method has been developed for the selective reductive N-alkylation of primary and secondary aromatic amines with some functionalized acetals using TFA/Et(3)SiH as a reagent combination. A variety of unsymmetrically substituted ethylenediamines can be synthesized in a one-pot procedure in excellent yields at room temperature. This new procedure offers significant advantages over previous synthetic approaches, including brevity, mild reaction conditions, excellent yields, and high functional group tolerance.