Efficient asymmetric synthesis of an azasugar in water

An extremely efficient asymmetric synthesis of a pyrrolidine azasugar was completed in only four steps in water, without the use of protecting groups and in 60% overall yield from a simple, achiral bis-electrophile.     

Strain fields at contacts between small particles

Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results.     

Dinitrogen reduction by TmII,DyII, and NdII with simple amide and aryloxide ligands

Dinitrogen can be reduced to the planar M2(mu-eta2:eta2-N2) structure without employing cyclopentadienyl or complicated polydentate ligands using the recently discovered divalent oxidation states of Tm(II), Dy(II), and Nd(II). Complexes of these ions with common monodentate amide and aryloxide ligands can effect N2 reduction. THF solutions of LnI2 (Ln = Tm, Dy) in the presence of 2 equiv of NaN(SiMe3)2 reduce dinitrogen to form {[(Me3Si)2N]2(THF)Ln}2(mu-eta2:eta2-N2) complexes that have planar Ln2N2 units and 1.264(7) and 1.305(6) A NN bonds consistent with (N2)2- moieties. With the stronger reductant Nd(II), aryloxides are sufficient ancillary ligands: the NdI2/2KOC6H3tBu2-2,6 (KOAr) system forms [(ArO)2(THF)2Nd]2(mu-eta2:eta2-N2), which has a 1.242(7) A NN bond.     

Thermal behaviourof complexes of antipyrine derivatives Part III.

The thermal behaviour of the mixed-ligand complexes of cobalt(II) and copper(I) ions with antipyrine derivatives of 1,2-ethanediamine or piperazine (BAMP and TAMEN), with water and with 2-mercapto-benzothiazole (Hmbt) was investigated. The complexes contain 2-mercaptobenzothiazole (Hmbt, in the case of cobalt(II) ion) or dimercaptobenzothiazine (mbt–mbt, in the case of copper(I) ion) molecules as ligands and perchlorate (ClO<sub>4</sub><sup>–</sup>) or thiocyanate (SCN – ) ion as counterion. By heating, water and ligands release the solid phase at lower temperature. At higher temperatures process of different organic reactions of ligands (e.g. polymerization, polycondensation) could be suggested to interpret the relative high final mass values.     

Reductive PET cycloreversion of oxetanes: singlet multiplicity, regioselectivity, and detection of olefin radical anion

Cycloreversion of 2-(p-cyanophenyl)-4-methyl-3-phenyloxetane (1) is achieved using 1-methoxynaphthalene (2) as electron-transfer photosensitizer. The experimental results are consistent with the reaction taking place from the singlet excited state of the sensitizer. Ring splitting of the radical anion 1*- occurs with cleavage of O-C2 and C3-C4 bonds, leading to products (acetaldehyde and p-cyanostilbene) different from the reagents used in the Paterno-Büchi synthesis of 1. The olefin radical anion involved in the electron-transfer process has been detected by means of laser flash photolysis.     

Kinetics of formation and dissociation of lanthanide(III) complexes with the 13-membered macrocyclic ligand TRITA4-

The tetraazamacrocyclic ligand TRITA(4-) is intermediate in size between the widely studied and medically used 12-membered DOTA(4-) and the 14-membered TETA(4-). The kinetic inertness of GdTRITA(-) was characterized by the rates of exchange reactions with Zn(2+) and Eu(3+). In the Zn(2+) exchange, a second order [H(+)] dependence was found for the pseudo-first-order rate constant (k(0)=(4.2 +/- 0.5) x 10(-7) s(-1); k'=(3.5 +/- 0.3) x 10(-1) M(-1)s(-1), k" =(1.4 +/- 0.4) x 10(3) M(-2)s(-1)). In the Eu(3+) exchange, at pH <5 the rate decreases with increasing concentration of the exchanging ion, which can be accounted for by the transitional formation of dinuclear GdTRITAEu(2+) species. At physiological pH, the kinetic inertness of GdTRITA(-) is considerably lower than that of GdDOTA(-)(t(1/2)= 444 h (25 degrees C) vs. 3.8 x 10(5) h (37 degrees C), respectively). However, GdTRITA(-) is still kinetically more inert than GdDTPA(2-), the most commonly used MRI contrast agent (t(1/2)= 127 h). The formation reactions of LnTRITA(-) complexes (Ln = Ce, Gd and Yb) proceed via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH(-) catalyzed process. The stability of the LnH(2)TRITA* intermediates (log K(LnH2L*)= 3.1-3.9) is lower than that of the DOTA-analogues. The rate constants of the OH(-) catalyzed step increase with decreasing lanthanide ion size, and are about twice as high as for DOTA-complexes.     

Description of the shape of thermoanalytical curves

Empirical parameters were chosen for the characterization of peaks (or steps) of thermoanalytical curves. The parameters were applied in studies on the repeatability, the relationship between kinetic constants and peak shape, the effect of sample thermal resistance. Kinetic constants can be estimated on the basis of peak shape parameters. Besides, approximate criteria were formulated for experiments allowing kinetic evaluation with the neglect of the heat transport within the sample. The empirical parameters were also used in checking the suitability of DSC data for purity analysis and in detecting changes of the thermal decomposition of papers caused by ageing.Zur Beschreibung von Peaks bzw. Stufen thermoanalytischer Kurven wurden emperische Parameter ermittelt, die bei der Untersuchung der Reproduziertbarkeit, der Beziehung zwischen kinetischen Konstanten und Peakform so wie des Einflusses des thermischen Wiederstandes der Probe angewendet wurden. Kinetische Konstanten können auf der Basis von Peakformparametern geschÄtzt werden. Weiterhin wurden Kriterien für Experimente ermittelt, die eine kinetische NÄherungslösung unter VernachlÄssigung des WÄrmetransportes innerhalb der Probe ermöglichen. Die empirischen Parameter wurden au\erdem bei der Untersuchung der Eignung von DSC-daten zur Reinheitsanalyse angewendet, weiterhin zum Nachweis von alterungsbedingten Änderungen der thermischen Zerzetzung von Papier.<hr>The authors express their thanks to Mrs E. Tóth for her valuable technical help. The permission to reproduce Figs 2–6 and 8–10 from Analytica Chimica Acta and Thermochimica Acta (Elsevier, Amsterdam) is also acknowledged.     

Synthesis of the Deuterium Labeled Isoflavone-<Emphasis Type="Italic">O</Emphasis>-glucoside 8,3′,5′-D<Subscript>3</Subscript>-Daidzin

The regio- and stereospecific glycosylation of 8,3′,5′-trideuterodaidzein &lt;strong class="EmphasisTypeBold ">1&lt;/strong> with α-acetobromoglucose to provide 8,3′,5′-trideuterodaidzein-7-&lt;em class="EmphasisTypeItalic ">O&lt;/em>-β-glucopyranoside &lt;strong class="EmphasisTypeBold ">2&lt;/strong> is presented.     

Preparation of diastereomeric 5,8-methanobenzoxazino[2,1–6]- and [2,3–6]-1,3-benzoxazin-4-ones by reaction of norbornane/ene-condensed dihydro-1,3-oxazines with salicyl chloride

Norbornane and norbornene-condensed dihydro-1,3-oxazines 1–6 were converted with salicyl chloride to 5,8-methanobenzoxazino[2,1–6]- and -[2,3-&lt;i>b&lt;/i>]-1,3-benzoxazin-4-ones 7–12. The addition takes place to the C ? N bond: after acylation, the intermediate is stabilized through cyclization to the aryl-substituted carbon by hydrogen chloride elimination. Diastereomers containing the oxazine rings in isomeric positions could be isolated in two cases. This is the first example of the isolation of diastereomers in such a salicyl chloride reaction. In contrast with earlier findings with reactions of related systems, no addition to the C ? C bond could be observed. The steric structures of the compounds were elucidated by ir, &lt;sup>1&lt;/sup>H- and &lt;sup>13&lt;/sup>C-nmr spectroscopy.     

Nucleocyclitols. Synthesis of substituted purinyl-muco-inositol derivatives

Several carbocyclic nucleoside analogs possessing a 6-substituted purine linked to a mesylated &lt;i>muco&lt;/i>-inositol were synthesized. The coupling of triethylamine-activated 6-chloropurine with 2,3-anhydro-l,5,6-tri-&lt;i>O&lt;/i>-(methanesulfonyl)-&lt;i>epi&lt;/i>-inositol gave a 6-chloro purinyl &lt;i>muco&lt;/i>-inositol amenable to further synthetic transformations in the heterocyclic moiety by substitution of the chlorine atom by nitrogen nucleophiles such as methylamino, diethylamino, benzylamino, hydrazino, morpholino, hydroxylamino, piperidino, and glycyl groups.