Volume 58, Issue 2-3

Treatment of germanium dioxide with a 33% aqueous solution of 1,2-diaminopropane (DAP) under solvothermal conditions leads to the formation of colourless octahedral crystals of the novel germanate (1,2-DAPH 2 ) 2 Ge 9 (OH) 4 O 18 · 2 H 2 O. The compound crystallises in the orthorhombic space group Pbca, a = 14.4155(10), b = 12.9384(9), c = 14.5417(8) Å,V =2712.2 (3) Å 3 ; Z =4. The structure consists of an anionic [Ge 9 (OH) 4 O 18 ] 4− framework with isolated [1,2-DAPH 2 ] 2+ cations and water molecules in the channels of the structure. The primary building units of the anionic framework are GeO 4 tetrahedra, GeO 5 trigonal bipyramids, and GeO 6 octahedra. The asymmetric unit consists of two GeO 5 units sharing a common edge to form a Ge 2 O 8 unit. This Ge 2 O 8 unit is corner-linked to two GeO 4 tetrahedra, and finally one GeO 4 tetrahedron is connected to a GeO 6 octahedron by cornersharing. The connectivity yields a chain-like Ge 5 O 19 fragment as a secondary building unit (SBU). The chain fragments are interconnected with each other forming the three-dimensional framework. Three types of channels with diameters ranging from 5.98 to 8.025 Å intersect the three-dimensional germanate network. Upon heating the compound decomposes in three steps starting at about 125˚C losing the water and the 1,2-diaminopropane molecules. In situ X-ray diffraction experiments show that the water molecules are removed retaining the integrity of the skeleton of the material. The removal of H 2 O is accompanied with an anisotropic shrinkage of the structure. The original lattice parameters were obtained after the uptake of water.

The oxidative coupling of various symmetric (5 -7) as well as unsymmetric silicon bisnaphtholates (11, 12), initiated by different oxidants (iron(III), cerium(IV), copper(II) or hypervalent iodine), furnishes the corresponding symmetric and unsymmetric binaphthols 13 - 17. The coupling reaction of the substrates follows strictly an intramolecular pathway.

Adducts of various acyclic enaminoketones and enaminoaldehydes with the Lewis acids boron trifluoride and triphenylboron were prepared. The adducts were characterized by NMR ( 1 H, 13 C, 11 B) and IR spectroscopy, FAB-MS, and X-ray crystal structure analysis of the adducts of (E)-3- diethylamino-3-phenyl-2-propenal with BF3 (4a) and BPh 3 (5a), respectively. The adduct formation occurs at the oxygen atom of the enaminocarbonyl compound and gives rise to a betainic structure with expressed equalization of the bond orders in the enaminocarbonyl moiety. The gas-phase structures of complexes 4a and 5a and of the corresponding free enaminoaldehyde were determined computationally by RHF and DFT methods, and a Natural Bond Orbital (NBO) analysis was undertaken.

The synthesis of new nucleosides by alkenylation of 5-iodo-2’-halo-2’-deoxyuridines with E-(1-tributylstannyl)-propene-1-ol via STILLE-coupling is described. The new compounds are characterized by 1 H NMR and elemental analysis. All nucleosides are evaluated by an enzymatic assay to be substrates of herpes simplex virus type 1 thymidine kinase (HSV-1 TK) and compared with uridine, thymidine and (E)-5-(2-iodovinyl)-2’-fluoro-2’-deoxyuridine (IVFRU).

The atroposelective ring opening of lactone-bridged biaryl systems is the key step in the total synthesis of a series of axially chiral biaryl natural products and useful reagents or catalysts for asymmetric synthesis. For a more in-depth understanding of the mechanism and stereochemical course of this remarkable cleavage reaction, a seven-membered ether analog of such useful biaryl lactones has been investigated structurally, both experimentally, by X-ray diffraction analysis, and by ab initio calculations (B3LYP/6-31G*). In a nearly perfect agreement, both methods show that these seven-membered bridged biaryls do not constitute helicene-like distorted molecules, but ‘true’ biaryls, whose sufficiently long lactone or ether bridge allows the two aromatic systems to adopt a large dihedral angle to each other, without any noticeable deviation from planarity for the two aromatic systems - in contrast to related six-membered analogs, which can rather be considered as helicene-like twisted polycyclic systems.