Facile preparation of benzo[4,5]thieno[2,3-b]pyridines and naphtho[b-4,5]thieno[2,3-b]pyridines via the reaction of Barton esters and benzynes

Titled compounds were prepared in a one-pot synthesis by generating symmetrically substituted benzyne intermediates by the diazotization of anthranilic acids in the presence of Barton esters. Unsymmetrically substituted aryne either gave mixtures of regioisomers or failed. However, nitro and methyl derivatives of titled compounds could be obtained as single products using appropriately substituted Barton esters.     

O,N‐Chelated Vanadium(IV) Oxo Aminophenolate Complexes: the Effect of Steric Bulk on the Vanadium Coordination Geometry. Can this Influence be detected Spectroscopically?

In order to study the effect of steric bulk on the vanadium coordination geometry in O, N‐chelated vanadium oxo (bis)phenolates, six different ortho‐aminophenolate ligands have been used. The ortho‐aminophenolate system was changed at three different places, i.e. 1) the second ortho position (C⁶) of the arene ring (R), 2) the substituents at the amino nitrogen (R′ and R″), and 3) the benzylic carbon atom (R*). The phenols were used in the preparation of the vanadium oxo (bis)phenolate complexes. In order to study whether it is possible to predict geometrical features of these vanadium complexes, UV/Vis, solution and frozen state EPR and ¹⁴N ESEEM spectroscopic data was measured and compared to the structural features of four structurally characterized vanadium oxo (bis)phenolates. Unfortunately, it turned out that is was not possible to correlate the EPR parameters, the UV/Vis HOMO‐LUMO transitions or ¹⁴N hyperfine couplings to the structural parameters.     

New total synthesis of the marine antitumor alkaloid (-)-agelastatin A

[reaction: see text] A new total synthesis of (-)-agelastatin A (1) has been achieved from the chiral oxazolidinone (-)-3. Although enone transposition was problematic when the Michael ring closure of 2 was attempted with strong base, the desired cyclization could be effected with Hunig's base after the pyrrole nucleus was brominated. Subsequent reduction and monobromination afforded synthetic (-)-agelastatin A (1).     

Oxyde des Thalliums

Analytical and Bioanalytical Chemistry -     

Verdoppelungen von Biokolloiden

Ohne Zusammenfassung     

Spiralenbildung bei Niederschlägen in Gallerten

Zusammenfassung Gelegentlich tritt eine Niederschlagsbildung in Gallerten als Spirale auf statt der Ringe oder der parallelen Scheiben. Da die Spirale auch dann als solche weiter wächst, wenn die Kontinuität der Keimwirkung unterbrochen war, wird angenommen, daß die Ursachen für beide Bildungsformen die gleichen seien.     

Kolloid-Symbiose

Ohne Zusammenfassung     

Untersuchung von Graphit

Ohne Zusammenfassung