RESUMEN
Reprocessing of spent nuclear fuel (SNF) is an important task in a frame of ecology and rational use of natural resources. Uranium, as the main component of SNF (>95%), can be recovered for further use as fresh nuclear fuel. To minimize an amount of solid radioactive waste generated during SNF reprocessing, new extractants are under investigation. Diamides of 1,10-phenanthroline-2,9-dicarboxylic acid are perspective tetradentate N-donor ligands that form strong complexes with f-elements, which are soluble in polar organic solvents. As an example of three ligands of this class, we conducted a comparative study and showed how the substituent in the amide functional group affects the extraction ability toward uranyl nitrate from nitric acid media. We have performed a careful study (NMR, FT-IR, XRD, RMC-EXAFS) of the structures of synthesized complexes of new ligands with uranyl nitrate and used quantum mechanical calculations to explain the discovered regularities through.
RESUMEN
Metal- and solvent-free reaction of quinolines with two molecules of aryltrifluoroacetylacetylenes afforded 3-arylethynyl-3-trifluoromethyl-1,3-oxazinoquinolines in up to 92% yields. The formation of a zwitterionic intermediate in the first step triggered a multistep domino reaction. This one-pot synthesis opens an easy access to novel quinoline derivatives bearing trifluoromethyl, acetylene and ketone functions, thus providing a powerful tool for drug design.
RESUMEN
Metal-free reaction between quinolines, aryltrifluoroacetylacetylenes and water at -18 °C-rt in MeCN resulted in stereoselective assembly of trifluoromethylated oxazinoquinolines with up to 99% yield that was essentially in contrast to a similar reaction with pyridines. The annulation proceeded via the 1,3-dipolar adducts of quinolines with trifluoroacetylacetylenes followed by intramolecular cyclization involving the trifluoroacetyl group and a molecule of water.
RESUMEN
The regioselective base-catalyzed addition of nitromethane to 2-oxo-4-trifluoromethyl-1,2-dihydropyrimidine-5-carboxylates is reported. It was found that the Michael-like pathway is highly reversible and substantially dominating under conditions of kinetic control (0-5 °C, 10 h) whereas the aza-Henry reaction leads to thermodynamically stable adducts after 8-24 h exposure at room temperature. The adjacent nitro and alkoxycarbonyl groups were exploited to demonstrate the synthetic potential of the obtained products by converting to the isomeric trifluoromethylated pyrrolo[3,4-d]pyrimidine-2,5-diones. With this aim an efficient protocol for selective reduction of nitro-derivatives to the corresponding 4- or 6-aminomethyl-2-oxo-4-trifluoromethyl-1,2,3,4-tetrahydropyrimidine-5-carboxylates and their subsequent thermal cyclocondensations was applied.
RESUMEN
Despite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional (2D) crystallization of heterocirculenes on a Au(111) surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D(8h)-symmetric sulflower (C16S8), whereas D(4h)-symmetric selenosulflower (C16S4Se4) forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C(1h)-symmetric selenosulflower (C16S5Se3) self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions.