α-Hydroxy ketones as useful templates in asymmetric reactions

Approaching the Nature's efficiency in controlling both reactivity and stereoselectivity of organic reactions by means of a catalyst species remains a formidable challenge for chemists to face. Despite impressive advances in the design of novel catalysts and activation modes, current catalytic and asymmetric methodologies rarely meet desirable standards of robustness, substrate scope, and selectivity altogether. One trick to improve catalyst behaviour is to identify adequate substrate template-catalyst combinations so that optimum performance of the reaction system could be achieved. During the last couple of years α-hydroxy ketones, and most particularly α'-hydroxy enones, have emerged as useful templates with applications in a number of metal-catalyzed as well as organocatalyzed C-C and C-X bond-forming stereoselective reactions. The first review of these accomplishments is presented here along with a brief historical introduction.     

β-Silylacrylate as a Multipurpose Reagent in Organic Synthesis

Acrylates are well known electrophilic alkenes having multitude of applications in organic synthesis. They are very good acceptors in Michael addition reactions and are good enophile/dienophile/dipolarophile partners in cycloaddition reactions. Replacing the β-alkyl/aryl groups in acrylates by a silicon group would be interesting. In addition to the conventional reactions displayed by acrylates, β-silylacrylates (β-SAs) can show reactivity specifically related to the silicon group. Many conventional organic reactions such as hydrodimerization, organocatalytic asymmetric Michael additions, inter- and intra-molecular Diels–Alder reactions, and asymmetric 1,3-dipolar cycloadditions have been used to generate the complex chemical entities from β-SAs. Some of the reaction outcomes were vastly influenced by the silicon substituent. This review describes the practical synthesis β-SAs and their use as starting point in complex molecule generation including total synthesis of some natural products/bioactive molecules.     

Why Are Selenouracils as Basic as but Stronger Acids than Uracil in the Gas Phase?

The gas‐phase basicity and acidity of 2‐selenouracil ( 2SU ), 4‐selenouracil ( 4SU ), and 2,4‐diselenouracil ( 24SU ) have been calculated at the B3LYP/6‐311+G(3df,2p) level of theory. Our results showed that all these compounds behave as bases of moderate strength in the gas phase. As was found for uracil and for the thiouracil analogues, the most basic site is the heteroatom at position 4, and only for 2SU is there a certain ambiguity in assigning the basic site. More importantly, with the only exception of 2SU , selenouracils are as basic as or slightly less basic than uracil, because the replacement of the oxygen atom at position 2 by a selenium atom leads to an increase of the electron delocalization inside the six‐membered ring, which decreases the intrinsic basicity of the heteroatom at position 4. As already reported for uracil and thiouracils, for selenouracils N1 is the most acidic site. However, selenouracils are predicted to be stronger acids than uracil. This acidity enhancement is essentially due to a specific stabilization of the anion when O is replaced by Se. Two factors are responsible for this stabilization: a significant aromatization of the ring upon deprotonation and a better dispersion of the excess electron density when the system contains third‐row atoms.     

Purification of RhIFN- in Bacteria Bodies with Acetic Acid-Water as Mobile Phase in RPLC

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α-Oxolactam enamines as new synthons in the Nenitzescu reaction

-Oxolactam enamines, namely, 3-piperidino-5,6-dihydropyridin-2(1H)-one (1a) and 3-piperidino-1,5,6,7-tetrahydroazepin-2-one (1b), were introduced for the first time into the Nenitzescu reaction. The processes yield cyclic adducts 3a—e, 6. On heating in acetic acid, they are transformed into benzofuropyridone 7 and benzofuroazepinones 10a,d, and 12 and, unexpectedly, into chromenopyrrole 8 and chromenopyridines 9a—d and 11.     

Synthesis,in silico and in vitro Evaluation of Novel Oxazolopyrimidines as Promising Anticancer Agents

New potential bioactive oxazolopyrimidines have been synthesized using two main approaches: the pyrimidine ring annulation on a functionalized oxazole and the benzoyl bromide trimerization followed by rearrangement and formation of the oxazolo[5,4-d]pyrimidine scaffold. The docking analyzes have shown that 7-piperazine substituted oxazolo[4,5-d]pyrimidines 8a – 8c could be potential VEGFR2 inhibitors with high free energy of ligand–protein complex formation (ΔG: −10.1, −9.6, −9.8 kcal/mol, respectively). In vitro antitumor assays confirmed theoretical predictions that oxazolo[4,5-d]pyrimidines 8a – 8c containing positively charged piperazine moiety should demonstrate significantly higher cytotoxic effects. 4-[5-(4-Chlorophenyl)-2-phenyl[1,3]oxazolo[4,5-d]pyrimidin-7-yl]piperazin-1-ium trifluoroacetate ( 8c ) exhibited a slightly higher antiproliferative effect (IC₅₀=0.21 μm ) than doxorubicin (IC₅₀=0.36 μm ) on MDA-MB-231 cell line and has relatively good results on OVCAR-3 (IC₅₀=1.7 μm ) and HCT-116 (IC₅₀=0.24 μm ) cells.     

Synthesis, Structural Characterization of Ferrocenyl Iminophosphines and Amidophosphines as Well as Their Application in the Suzuki Reaction

Ferrocenyliminophosphine 1 and 1,1'-bisferrocenyliminophosphine 2 were easily prepared from the condensation of formylferrocene or 1,1'-diformylferrocene with 2-(diphenylphosphino)aniline.The following reduction of imine group by LiAlH4 led to the formation of the corresponding ferrocenyl amidophosphines 3 and 4.The new ligands 2-4 were well characterized by IR,1H NMR,31P NMR spectra,elemental analysis,and ESI-MS.The catalytic activity of all the ligands with palladium compounds in the Suzuki reaction was evaluated.Ligand 1,in combination with Pd(OAc)2,was found to be the most effective for the Suzuki reaction of aryl bromides with phenylboronic acid.Typically,the use of 0.1%(molar fraction)of Pd(OAc)2/ligand 1 in the presence of two equivalents of K2CO3 as base in toluene at 110 ℃ provided good to excellent yields of the coupled products.     

Ampholytes as background electrolytes in capillary zone electrophoresis: sense or nonsense? Histidine as a model ampholyte

A lot of phenomena, occuring in capillary zone electrophoresis (CZE), are linked with the ionic concentration of the background electrolyte (BGE). If weak bases and acids are used as BGEs in CZE, at a pH where they are scarcely ionized, the ionic concentration of the BGE is very low and this brings a strong peak broadening, limited sample stacking and low sample load. Because the electromigration dispersion increases extremely, moreover, the existence of low-conductivity BGEs in CZE is a contradiction in terms. The behavior of ampholytes as BGE in CZE is examined, by means of histidine as a model ampholyte. For BGEs consisting of histidine, important parameters, including the ionic concentrations, buffer capacity, transfer ratio, and the indicator for electromigration dispersion E(1)m(1)/E(2)m(2), are calculated at various pH. Although the transfer ratio is fairly constant over the whole pH traject, the ionic concentration and buffer capacity decrease whereas the electromigration dispersion strongly increases near the pI of histidine. I.e., that ampholytes can be applied as BGEs in CZE, however, just not at pH near their pI value, except as the difference between the pK values of the basic and acidic group, the deltapK value, is very small. For ampholytes with a low deltapK value or at high concentrations, all the before-mentioned effects are less fatal, but in that case we can not speak of a real low-conductivity BGE. If ampholytes are used at pH near their pK values, the use of ampholytes as BGE is not advantageously compared with simple weak bases and acids. This has been confirmed by calculations and experiments.     

N-Picolinamides as ligands in Ullman type C–O coupling reactions

Copper-catalyzed modified Ullmann coupling reactions creating C–O bonds, including diaryl ethers or phenols, are vital to organic synthesis. Synthesized N-phenyl-2-pyridinecarboxamide and its derivatives were used as ligands in conjunction with catalytic copper sources in the formation of various diaryl ethers and phenols. Various aryl and heteroaryl halides with electron donating and withdrawing groups were reacted with various phenols under mild reaction conditions providing moderate to excellent yields.     

Aminopyridines as amino components in the catalytic synthesis of α-aminophosphonates

6h-Aminophosphonates containing alicyclic, aromatic, and heterocyclic fragments were obtained in high yields by the Kabachnick—Fields reaction of the corresponding carbonyl compounds with 2-, 3- and 4-aminopyridines and diethyl phosphite using tetra- tert-butyl- phthalocyanine aluminum chloride as the catalyst. 2-, 3-, 4-Aminopyridines were found to vary in their reactivity with ketones and diethyl phosphite in the catalytic three-component one-pot process.     

Benzosuberyl Substituents as a “Sandwich-like” Function in Olefin Polymerization Catalysis

For the rational design of metal catalyst in olefin polymerization catalysis, various strategies were applied to suppress the chain transfer by bulking up the axial positions of the metal center, among which the "sandwich" type turned out to be an efficient category in achieving high molecular weight polyolefin. In the α-diimine system, the "sandwich" type catalysts were built using the typical 8-aryl-naphthyl framework. In this contribution, by introducing the rotationally restrained benzosuberyl substituent into the ortho-position of N-aryl rings, a new class of "sandwich-like" α-diimine nickel catalysts was constructed and fully identified. The rotationally restrained benzosuberyl substituents played a "sandwich-like" function by capping the nickel center from two axial sites. Compared to the nickel catalyst Ni1 bearing freely rotated benzhydryl substituent, Ni2 featuring benzosuberyl substituent enabled the increase(8 times) of polymer molecular weights from 8 kDa to 65 kDa in the polymerization of ethylene. By further increasing the steric bulk of another ortho-site of the N-aryl ring, the polymer molecular weight even reached an ultrahigh level of 833 kDa(M_w=1857 kDa) using the optimized Ni3. Notably, these nickel catalysts could also mediate the copolymerization of ethylene with methyl 10-undecenoate, with Ni3 giving the highest copolymer molecular weight(88 kDa) and the highest incorporation of comonmer(2.0 mol%), along with high activity of up to 10~5 g·mol~(-1)·h~(-1).     

Carbon materials as electrodes for electrosorption of NaCl in aqueous solutions

Different porous carbons (MWCNT, a carbon aerogel, an activated carbon cloth and a chemically activated carbon) were evaluated as electrode material for the electrosorption of NaCl. The results obtained from the chronoamperometric experiments were correlated to the surface area and the size of the pores present in each carbon. These results indicate that all the surfaces are equivalent for the electrosorption process, demonstrating that both, mesopores and micropores, are equally effective. Nevertheless, the kinetics of the process is influenced by the pore size distribution of the carbon, although it is rather fast for all the carbons studied. The chemically activated carbon seems to be the most suitable carbon material for electrosorption of NaCl due to the combination of a high surface area and an appropriate pore size distribution.     

Hydrazine reagents as derivatizing agents in environmental analysis – a critical review

Hydrazine reagents are a well-known group of derivatizing agents for the determination of aldehydes and ketones in liquid and gaseous samples. Within this article, the most important hydrazine reagents are critically summarized, and their major applications in different fields, including environmental analysis, food chemistry and industrial analysis are introduced. As 2,4-dinitrophenylhydrazine (DNPH) is the basic reagent for several international standard procedures, its properties are discussed in detail. Particular focus is directed on the chemistry of the hydrazine reagents, and chemical interferences are considered. Recent methods for the determination of various oxidants using hydrazine reagents are presented as well. Due to limited space, this review does not cover the related field of carbohydrate analysis, although many chemical aspects are similar.     

Reduction of the quinizarin molecule in methanol as studied by γ-radiolysis

The disproportionation of quinizarin semiquinones in methanol solutions of different pH has been investigated using the -radiolysis method. After⁶⁰Co-irradiation of deaerated solutions the corresponding changes in the optical absorption spectra were recorded. In solutions of different pH the semiquinones disproportionate to give appropriate forms of quinizarin hydroquione which can react with oxygen to regenerate the parent compound. In neutral and acidic methanol the corresponding form of hydroquinone (1,4,9,10-tetrahydroxyanthracene) undergoes a transformation leading to formation of 9,10-dihydroxy-2,3-dihydro-1,4-anthraquinone which is unreactive towards oxygen.     

Aromatic Amines as Co‐sensitizers in Dye Sensitized Titania Solar Cells

Abstract

Solar cells based on titania require the use of sensitizing dyes in order to make the absorption band coincident with the solar spectrum. The most successful sensitizing dyes are based on Ru‐bipyridyls and are chosen for their absorption and redox characteristics. In addition to absorbing visible light, the sensitizing dye injects an electron from its excited state into the band gap of the titania. The injected electron must be conducted through the titania to an electrode upon which the titania is coated. One of the energy wasting pathways available to the injected electron is back transfer to an oxidized dye species on the surface of the titania. We have discovered a simple means of alleviating this energy wasting pathway by anchoring aromatic amines, i.e., co‐sensitizers, at low concentration along with the Ru‐based bipyridyl sensitizing dye to the surface of titania nanoparticles. Our results indicate that there is a significant increase in cell efficiency (～15% at AM 1.5, area ≥1 cm²) primarily due to an increase in current when these species are present on the surface in combination with the dyes. We will report our preliminary results on a series of co‐sensitizers, and we will compare these to literature findings which use similar compounds as either co‐adsorbed species on titania or as substituents on the sensitizing dye molecule itself.     

Peracetylated β-cyclodextrin as additive in enzymatic reactions: enhanced reaction rate and enantiomeric ratio in lipase-catalyzed transesterifications in organic solvents

Peracetylated β-cyclodextrin has been employed as a macrocyclic additive to enhance the enantiomeric ratio E and reaction rate in Pseudomonas cepacia lipase (PSL)-catalyzed enantioselective transesterification of 1-(2-furyl)ethanol in organic solvents. The beneficial action of the cyclodextrin used as a regulator of lipase was tentatively interpreted as increasing the conformational flexibility of the enzyme and undergoing host–guest complexation with the product, thereby preventing product inhibition and leading to an enhancement of the enantiomeric ratio E and the reaction rate. The effect of the organic solvent on the present cyclodextrin-mediated enzymatic transesterification has been studied.     

α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions

A group of tridentate Schiff bases derived from (+)-α-pinene were synthesized. The steric effects in the transition state, the importance of π-π stacking interactions as well as the electronic effects of aryl aldehydes according to Hammett constant values in the enantioselective addition of Et₂Zn to aldehydes with the use of Schiff bases as chiral ligands are described. Also, a variety of aldehydes were cyanated using a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases. The influence of a conjugated double-bond in the cyanation substrates on enantioselectivity was observed. The chemical structures of the chiral Schiff base-titanium alkoxide complexes are discussed based on their ¹H and ¹³C NMR spectra. 3D models of the Zn₂-complex catalyst and Ti-complex catalyst containing α-pinane-type Schiff bases based on X-ray diffraction experiments are postulated. The models presented were consistent with the reported chirality of the addition product and observed ee.     

Diethyl Tartrate on Polystyrene Bead as Chiral Stationary Phase in Liquid Chromatography

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