Enantioselective Total Synthesis of (−)‐Blennolide A

Blennolide A can be synthesized through an enantioselective domino‐Wacker/carbonylation/methoxylation reaction of 7 a with 96 % ee and an enantioselective Wacker oxidation of 7 b with 89 % ee. Further transformations led to the α,β‐unsaturated ester (E)‐ 17 , which was subjected to a highly selective Michael addition, introducing a methyl group to give 18 a . After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (?)‐blennolide A (ent‐ 1 ) in a few steps.     

Spektroskopische Untersuchungen zur Frage der hydrophoben Bindungen

Colloid and Polymer Science - Mit Hilfe der NIR-Spektroskopie und der UV-Spektroskopie wurde versucht, die Ausbildung hydrophober Bindungen in wäßrigen Lösungen einheitlicher,...     

Microscopic magnetic properties of nonstoichiometric V2O3+x—NMR and inelastic spin-flip neutron scattering measurements

The local magnetic properties of the V sites in the nonstoichiometric V₂O_3+x (0 ? x <0.08) have been examined by nuclear magnetic resonance and inelastic spin-flip neutron scattering techniques. The samples with x = 0.01 and 0.02 show a paramagnetic metal (PM)-antiferromagnetic insulator (AFI) transition. In the AFI phase, two distinct ⁵¹V NMR signals with hyperfine fields H_n = 184.9±0.5 kOe and 71±1 kOe were observed at 1.8 K, which were assigned as due to V³⁺ and V³⁺ sites, respectively. On the other hand, the samples with x = 0.04 and 0.06 were metallic down to 1.4K, and showed a paramagnetic (PM)-antiferromagnetic (AFM) transition at about 10 K. In these samples, a ⁵¹V NMR signal with H_n = 58±2 k0e and one with 〈H_n〉 = 9kOe were observed at 1.8 K, which were assigned as due to V³⁺-like sites and the matrix V sites, respectively. These results are entirely consistent with those obtained from the neutron experiment. We propose that in the metallic phase (0.04 ? x < 0.08) the minority V⁴⁺-like sites are magnetically localized in the delocalized V matrix and may be responsible for the antiferromagnetic long range order below 10 K.     

Die Struktur kollagenähn licher Homo- und Heteropolytripeptide. 2. Mitt. Untersuchung des Tripelhelix-Knäuel-Übergangs an (L-Pro-L-Ala-Gly-L-Pro-L-Ala-Gly)-Oligomeren

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Tunneling motions of methyl groups in manganese acetate tetrahydrate

The temperature dependence of the tunneling motions of the methyl groups in Manganese Acetate Tetrahydrate has been studied by high resolution inelastic neutron scattering in a range between 0.06 K and 40 K. The results are in qualitative agreement with models based on rotor-phonon and rotor-rotor coupling valid for temperature regions above and below 5 K respectively. The finite line width of one of the tunneling lines which persists at very low temperatures and the anomalous positive shift of the same line at higher temperatures is not understood.