Search results for "ta116"
showing 10 items of 942 documents
Asymmetric Synthesis of Functionalized Tricyclic Chromanes via an Organocatalytic Triple Domino Reaction
2017
A highly stereoselective triple domino reaction for the synthesis of functionalized tricyclic chromane scaffolds has been developed. A secondary amine-catalyzed domino Michael/Michael/aldol condensation reaction between aliphatic aldehydes, nitro-chromenes, and α,β-unsaturated aldehydes leads to the formation of synthetically important tricyclic chromanes bearing four contiguous stereogenic centers including a tetrasubstituted carbon in good yields (20–66%) and excellent stereoselectivities (>20:1 dr and >99% ee).
Synthetic Studies towards Pectenotoxin-2: Synthesis of the Nonanomeric 10-epi-ABCDE Ring Segment by Kinetic Spiroketalization
2011
The synthesis of the nonanomeric 10-epi-ABCDE ring system of pectenotoxin-2 has been achieved by using a kinetic spiroketalization reaction. The synthesis of the spiroketalization precursor was achieved through a cross-metathesis/hydro-genation sequence. The formation of the epi-C10 isomer resulted from an unexpected anti-Felkin selective addition of organometallic nucleophiles to the advanced CDE ring precursor. This addition reaction was investigated with differently protected α,β-dioxygenated model aldehydes, which displayed similar anti-Felkin selectivities with organometallic nucleophiles.
Pseudopeptidic ligands: exploring the self-assembly of isophthaloylbisglycine (H2IBG) and divalent metal ions.
2012
We present a systematic study of the complexation of the new pseudopeptidic ligand isophthaloylbisglycine (H(2)IBG) with divalent metal ions of varying ionic radius. This work represents the initial employment of H(2)IBG in the coordination chemistry of alkaline earth, 3d transition, Zn(II) and Cd(II) metal elements. Infrared, NMR, thermal, magnetic, adsorption and theoretical studies of these compounds are also discussed.
Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions
2016
A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.
Self-assembly properties of bile acid derivatives of L-cysteine, L-valine and L-serine alkyl esters
2012
Comprehensive self-assembly studies for nine bile acid amides of amino acid esters are reported. The number of the hydroxyl groups attached to the steroidal skeleton and the character of the amino acid ester moiety were used as variables when examining the self-assembly properties of the compounds. Two of the compounds were shown to undergo self-assembly leading to organogelation. In addition, preliminary self-assembly studies in aqueous mixtures of polar organic solvents were conducted. Microscopic methods (optical microscopy and scanning electron microscopy) were utilised in order to gain a deeper insight into the self-assembled structures. Furthermore, single-crystal X-ray structures for…
Aqueous self-assembly and cation selectivity of cobaltabisdicarbollide dianionic dumbbells.
2014
The anion [3,3'-Co(C2B9H11)2](-) ([COSAN](-)) produces aggregates in water. These aggregates are interpreted to be the result of C-H⋅⋅⋅H-B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN](-) units. The approach is to join two [COSAN](-) anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K(+) selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K(+) from a mixture containing Li(+), Na(+), …
Alkaline Pre-treatment of Hardwood Chips Prior to Delignification
2013
Scots pine (Pinus sylvestris) chips were pre-treated with alkaline solutions (alkali charges of 1, 2, 3, 4, 6, and 8% of NaOH on the oven-dried wood material) at 130°C and 150°C for various treatment times (30, 60, 90, and 120 minutes). Under these conditions, 2.0–13.6% of the wood d.s. was dissolved into the aqueous hydrolysates. The soluble organic fraction was primarily characterized in terms of carbohydrates (monosaccharides and oligo-/polysaccharides) and their alkali-catalyzed degradation products: aliphatic carboxylic acids containing, besides non-volatile hydroxy carboxylic acids, volatile formic and acetic acids. With increasing alkali charge, temperature, and time, the enhanced fo…
A novel bisphosphonate-based solid phase method for effective removal of chromium(iii) from aqueous solutions and tannery effluents
2013
Effective removal of chromium(III) from waste waters e.g. in the leather industry is required due to continuously tightening environmental regulations, and several methods such as precipitation and adsorption are currently in use. Nevertheless, more efficient, straightforward and inexpensive methods are constantly being sought. The current study describes a novel method to separate chromium(III) from aqueous solutions based on the use of solid bisphosphonates with a P–C–P backbone. Five classes of bisphosphonates with different functional groups and alkyl chain lengths at the center carbon, in all 16 compounds, were prepared and their suitability for metal ion complexing as chelating agents…
Pyrolysis of Tall Oil-Derived Fatty and Resin Acid Mixtures
2012
Neutralised mixtures of tall oil-derived fatty acids and resin acids were separately pyrolysed (at 750∘C for 20 s) by pyrolysis gas chromatography with mass-selective and flame ionisation detection (Py-GC/MSD/FID) to clarify their thermochemical behaviour. The pyrolysate of fatty acid salts characteristically contained high amounts of unsaturated aliphatic hydrocarbons and minor amounts of monoaromatics, whereas the pyrolysis of resin acid salts mainly resulted in the formation of aromatics with up to three benzene rings and only in very low amounts of aliphatic hydrocarbons. The data obtained are useful when considering the suitability of various tall oil products containing fatty and resi…
Uranyl(VI) complexes with a diaminobisphenol from eugenol and N-(2-aminoethyl)morpholine: Syntheses, structures and extraction studies
2011
Abstract The syntheses and structural studies of an [O,N,O,N′]-type phenolic ligand [(N’,N’-bis(2-hydroxy-3-methoxy-5-(propen-2-yl)benzyl)-N-(2-aminoethyl)morpholine), (H2L) and two new uranyl complexes of this ligand are described. The reaction between uranyl nitrate hexahydrate and H2L in a 1:2 M ratio (M to H2L) results in a uranyl complex of the formula [UO2(HL)(NO3)(H2O)] (1). In the presence of a base (triethylamine), with the same molar ratio, the uranyl complex [UO2(HL)2]·2CH3CN (2) is formed. The molecular structures H2L, 1 and 2 were verified by X-ray crystallography. Both uranyl complexes are zwitterions with a neutral net charge. A comprehensive NMR-structural analyses of all co…