Synthesis of bis(polyfluoroalkyl)-1,3,5-triketones

A preparative procedure was developed for the synthesis of polyfluoroalkyl-1,3,5-triketones by condensation of acetone or fluorinated methyl -diketones with methyl perfluorocarboxylates in the presence of LiH. In the case of CF₃ substituents, the formation of triketone was accompanied by the formation of its cyclic hydrate, viz., of dihydroxytetrahydropyranone.     

Isolation and characterization of tautomeric forms of 2,4-diacetyl-3-(<Emphasis Type="Italic">o</Emphasis>-R-aryl)-5-hydroxy-5-methylcyclohexanones

Keto-enol prototropic tautomerism of 2,4-diacetyl-3-(o-R-aryl)-5-hydroxy-5-methylcyclohexanones in the -diketone fragment was studied. Individual tautomeric forms of -diketones, viz., keto and enol forms, were isolated and characterized. The latter are generated through enolization of the alicyclic carbonyl group. Enolization is facilitated by the presence of an ortho substituent in the benzene ring.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2670–2674, December, 2004.     

The effects of solute-solvent interactions on the electronic visible spectra of bis(β-diketonato)oxovanadium(IV) complexes

Summary The solvatochromic behaviour of bis(-diketonato)oxovanadium(IV) complexes is quantitatively correlated by an approach that models specific and non-specific solute-solvent interactions. The applicability of the Selbin-Gutmann relation is discussed. The solvent-induced spectral shifts in VO(acac)₂ are dominated by specific interactions of the donor-acceptor type, whereas for VO(tfa)₂, the nonspecific solute-solvent interactions make the dominant contribution.

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Der Einfluß von Wechselwirkungen zwischen Lösungsmittel und gelöstem Stoff auf die VIS-Spektren von Bis(-diketonato)oxovanadium(IV)-Komplexen

Zusammenfassung Das solvatochrome Verhalten von Bis(-diketonato)oxovanadium(IV)-Komplexen wird mit einem Modell, das spezifische und nichtspezifische Wechselwirkungen in Lösung berücksichtigt, quantitativ beschrieben. Es wird die Anwendbarkeit der Selbin-Gutmann-Relation diskutiert. Die Solvens-induzierten Verschiebungen in den VIS-Spektren von VO(acac)₂ werden von den spezifischen Wechselwirkungen vom Donor-Acceptor-Typ bestimmt, währenddessen für VO(tfa)₂ die nichtspezifischen Wechselwirkungen zwischen Substrat und Lösungsmittel den dominierenden Beitrag liefern.

     

A practical method for synthesis of stable phosphorus ylides in aqueous media

A convenient one-pot synthesis of stable phosphorus ylides by the condensation of triphenylphosphine with dialkyl acetylenedicarboxylate and CH acids, such as penta-2,4-dione or diethyl propane-1,3-dioate, in the presence of -cyclodextrin as a catalyst (to increase the solubility of the reactants in water) without using toxic organic solvents was proposed. This methodology is of interest due to the use of water as a solvent, thus minimizing such factors as the cost, operational hazards, and environmental pollution.     

Phenolic Components of Empetrum nigrum Extract and the Crystal Structure of One of Them

Four phenolic components are isolated from the CHCl ₃ extract ofEmpetrum nigrumL. Three of them are known from this plant. The fourth (6,8-dimethylpinocembrine) is isolated from crowberry for the first time. The previously proposed structure for 2'-methoxy-4'-hydroxy- ,-dihydrochalcone is confirmed by x-ray structure analysis     

Kinetic method for the study of xylan hydrolysis by xylan hydrolases

Summary The Somogyi-Nelson colorimetric method was used in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of xylan catalyzed by xylan hydrolases. The values of the Michaelis parameters (Km=5.56 g l^–1 andV=2.94 · 10^–5 M s^–1) were determined.

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Eine kinetische Methode zur Untersuchung der Hydrolyse von Xylan durch Xylan-Hydrolase

Zusammenfassung Die kolorimetrische Methode nach Somogyi-Nelson wurde nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Xylan, katalysiert durch Xylan-Hydrolasen vonAspergillus oryzae, angewandt. Es wurden die Michaelis-Parameter (Km=5.56 g l^–1 undV=2.94 · 10^–5 M s^–1) bestimmt.

     

Crystal and Molecular Structure of Cu(II) Bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate)

A new compound from the series of alkoxyketoiminates, Cu(II) bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate), has been synthesized and studied by X-ray crystallography. Crystal data for CuO₄N₂C₂₀H₃₆: a=10.154(1), b=9.921(1), c=11.684(2) , =96.17(1)°, space group P2₁/c, Z=2, dcalc =1.226 g/cm³, R=0.037. The structure is molecular and built from isolated trans-complexes. The copper atom has a plane square environment of two oxygen atoms (Cu–O 1.93 ) and two nitrogen atoms (Cu–N 1.90 ). The O–Cu–N chelate angle is 91.7°. The complex has an intramolecular hydrogen bond, N–H...O 2.16 , involving the alkoxy oxygen atom. The molecular packing in the crystal is close to that of copper(II) dipivaloylmethanate. The calculated van der Waals intermolecular interaction energies and thermogravimetric characteristics of the complexes are compared.     

The Influence of β-Diketones on the Hydrolysis and Growth of Particles from Zirconium(IV) n-Propoxide

The influence of low ligand/Zr mole ratios ( = 0–0.1) on the hydrolysis and growth of oligomers from Zr(O ⁿ Pr)₄ modified with a series of -diketones (trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, dibenzoylmethane and dipivaloylmethane), and their subsequent aggregation to form uniform, dense spheres, has been investigated by light scattering and turbidometry. The addition of -diketones results in a large increase in the induction time, t _i (reduction in hydrolysis/condensation rates). A remarkable feature of the data is the dramatic reductions in rate observed even when a maximum of one in forty Zr–OR bonds have been replaced by the -diketone and are no longer available for hydrolysis or further condensation. The largest effect is observed with dibenzoylmethane, which increases t _i by a factor of 26 relative to acetylacetone.A mechanism rationalising the origin of the effect is discussed, which involves segregation of the -diketone ligands on the surface of the growing particle, with subsequent particle growth restricted to those sites not occupied by the chelating ligands.     

Condensation of 1-Substituted 5-Aminopyrazoles with β-Dicarbonyl Compounds

Condensation of N-substituted 5-aminopyrazoles with -diketones occurs with the formation of pyrazolo[4,5-b]pyridines. Depending on the conditions, their reaction with -keto acids can give either 6-oxo- or 4-oxopyrazolo[4,5-b]pyridines.     

A kinetic method for the direct determination of cellobiose hydrolysis by β-glucosidases

TheSomogyi—Nelson colorimetric method is applied in a new manner which is more suitable for following the kinetics of cellobiose hydrolysis catalyzed by -glucosidase (EC 3.2.1.21). TheSomogyi—Nelson colour reagent, which is a mixture of the solutions of the reagent ofSomogyi and that ofNelson in a volume ratio of 1:1, is added to the enzyme-substrate solution at the very start of the reaction. The colour reagent reacts with the product (D-glucose). Under the reaction conditions (0.1M acetate buffer,pH = 5.0 and temperature 37°C) the colour reagent does not affect the enzyme activity. The method excludes any inhibition of the product, owing to the continuous removal of the latter by the colour reagent. The method suggested has been applied to monitor cellobiose hydrolysis with -glucosidase, contained in four cellulase enzyme preparations from various fungal sources. The values of theMichaelis parameters (Km, V) were determined.

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Eine kinetische Methode zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Cellobiose, katalysiert durch -Glucosidase (EC 3.2.1.21), angewandt. Das Farbreagenz nachSomogyi undNelson (Mischung der Reagenzien vonSomogyi undNelson im Volumenverhältnis 1:1) wird der Enzym-Substrat-Lösung zu Beginn der Reaktion hinzugefügt. Das Farbreagenz tritt mit derD-Glukose in Reaktion, wobei unter den gegebenen Reaktionsbedingungen (0,1M Azetatpuffer,pH = 5,0 und 37°C) die Enzymaktivität nicht beeinflußt wird. Die entwickelte Methode wurde zur Verfolgung der Hydrolyse von Cellobiose durch ß-Glucosidasen, die in vier Enzympräparaten aus verschiedenen Pilzstämmen enthalten waren, angewandt. Es wurden dieMichaelis-Parameter (Km, V) bestimmt.

     

Semiempirical calculations on cyclodextrins

In order to obtain information on the different reactivities of the hydroxyl groups of the glucopyranose units or the inclusion complex formation mechanism, the charge distributions and the geometrical constraints must be determined. Geometry optimizations, employing the AM1 semiempirical method, have been performed for -D-glucopyranose, –,–, and -cyclodextrins. The data obtained were compared with X-ray diffraction data of the cyclodextrins.Dedicated to Professor József Szejtli.     

Porphyrins. 38. Reaction of Porphyrins Containing Hydroxy(alkoxy)ethyl or Alkoxymethyl Substituents with Nucleophiles in the Presence of Zinc Acetate. A Novel, Promising Method for the Modification of Porphyrins on the Periphery of the Macrocycle

Porphyrins which contain 1-hydroxy(alkoxy)ethyl or alkoxymethyl substituents on the periphery of the macrocycle (i.e. formally able to yield benzyl type carbocations) react with nucleophiles (4-tert-butylphenol or the -diketones acetylacetone, benzoylacetone, dibenzoylmethane, or 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione) in the presence of excess zinc acetate. They give high yields of the corresponding addition products, which are the zinc complexes of porphyrins with a 1-(4-tert-butylphenoxy)ethyl substituent or with substituents containing -diketone residues.     

1H,13C and19FNMR studies on the structure of the intramolecularly hydrogen bondedcis-enols of 2-trifluoroacetylcycloalkanones

Summary The¹H,¹³C and¹⁹F NMR spectra of some 2-trifluoroacetylcycloalkanones comprising five-, six-, seven-, and eight-membered ring systems have been studied. These systems have been shown by¹⁹F NMR spectroscopy to be over 90% enolized. The effects of ring size on the¹H,¹³C and¹⁹F chemical shifts and¹³C-¹⁹F coupling constants are discussed. The direction of enolization in these systems was investigated by¹H,¹³C and¹⁹F NMR spectroscopy and evidences were presented in favour of a dominant exocyclic enol form in the five- and an endocyclic enol form in the six-, seven- and eight-membered ring systems.

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¹H-,¹³C- und¹⁹F-NMR-Untersuchungen zur Struktur der intramolekularen Wasserstoffbindung in dencis-Enolen von 2-Trifluoracetylcycloalkanonen

Zusammenfassung Die¹H-,¹³C- und¹⁹F-NMR-Spektren einiger 2-Trifluoracetylcycloalkanone mit fünf-, sechs-, sieben- und achtgliedrigen Ringsystemen wurden untersucht. Mittels¹⁹F-NMR konnte über 90% Enolisierung nachgewiesen werden. Der Effekt der Ringgröße auf die chemischen Verschiebungen in den¹H-,¹³C- und¹⁹F-NMR-Spektren und auf die¹³C-¹⁹F-Kopplungskonstanten werden diskutiert. Die Enolisierungsrichtung dieser Systeme wurde unter Einsatz der NMR-Spektren untersucht: dabei ergab sich eine dominierende exocyclische Enolform für die Fünfringe und eine endocyclische Enolform für die sechs-, sieben- und achtgliedrigen Ringe.

     

Asymmetrical synthesis of organometallic analogs of natural compounds. 8. Reactions of pentafluorobenzaldehyde with the Ni(II) complex of a schiff base of glycine and (S)-2-[N-(benzylprolyl)amino]benzophenone

Reaction of pentafluorobenzaldehyde with a Ni(II) complex of a Schiff base formed from glycine and (S)-2-[N-(benzylprolyl)amino]benzophenone yields, depending on the reaction conditions, the hitherto unknown, diastereo-and enantiomerically pure amino acids 2R,3S--(4-methoxytetrafluorophenyl)serine, 2S,3R--(4-methoxytetrafluorophenyl)serine, 2S,3S--(pentafluorophenyl)serine, and 2S,3R--(pentafluorophenyl)serine.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Institute of Bioorganic Chemistry and Petroleum Chemistry, Ukrainian Academy of Sciences, 252028 Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 687–693, March, 1992.     

Interaction of fluoroalkyl-containing β-diketones with amines

The composition of products of the interaction of asymmetric fluoroalkyl-containing -diketones with amines was studied. Mixtures of regioisomeric -aminovinylketones and products of cleavage and secondary condensation are formed, depending on the temperature, the solvent, the nature of the fluorinated and nonfluorinated substituents in the -diketone, and the basicity of the amine. The major product is a -aminovinylketone in which the NH₂ group is removed from the fluoroalkyl substituent. No -aminovinylimines, products of condensation involving two electrophilic centers, were observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2278–2284, September, 1996.     

Binding of vitamin A byβ-cyclodextrin and heptakis(2,6-O-dimethyl)-β-cyclodextrin

Inclusion complexation of all-trans-retinol, retinal and retinoic acid with -cyclodextrin (-CD) and heptakis(2,6-O-dimethyl)--cyclodextrin (DM--CD) were investigated by means of UV-vis spectroscopy. The association constants (K _a) obtained for vitamin A with DM--CD is greater than with -CD. On the other hand, for the same host compoundK _a values of retinol, retinal and retinoic acid are very close to each other.     

Solute-solvent effects in the acidic dissociation of the ampholyte N-tris(hydroxymethyl)methylglycine (“tricine”) in 50 mass % methanol-water solvent

The pK values for the two acidic dissociation steps of the ampholyte N-tris-(hydroxymethyl)methylglycine (tricine) in 50 mass % methanol-water solvent have been determined by emf measurements of cells of the type Pt|H₂(g, 1 atm), tricine buffer, Br^–, AgBr|Ag over the range 5 to 50°C (pK ₁)and 5 to 60°C (pK ₂).The standard thermodynamic quantities H^o, S^o, and C _p ^o for the two dissociation processes have been derived and are compared with the corresponding values for tricine and the parent glycine in water and with those for other acids in 50 mass % methanol-water solvent. Both tricine and protonated tricine become weaker acids when methanol is added to the aqueous solvent. It appears that a strong stabilization of the zwitterion in water is responsible for this behavior. This conclusion is supported by comparing the changes in entropy and heat capacity for the dissociation of tricine with the values of these quantities for the dissociation of model acids of simple structure, such as ammonium ion and acetic acid.On leave 1971–1973 from Drury College, Springfield, Missouri     

Quantum chemical studies on electrophilic addition

The geometries of the 2-hydroxyethyl and isomeric oxiranium cations have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set. These species are possible intermediates in both the electrophilic addition of OH to ethylene and in the acid catalysed ring opening of oxirane. The optimized structures were then used to compute more accurate wave functions using Dunning's double-zeta basis set, and with this large basis set the bridged oxiranium ion was found to be the more stable by 7.2 kcal/mole. The barrier to interconversion of these two C₂H₄OH ions was computed to be 25.0 kcal/mole above the oxiranium ion.     

Preferential inclusion of food colours via formation of their inclusion complexes withβ-cyclodextrin (β-CD)

The encapsulation of commercially utilized food colours with-cyclodextrin is reported. Thus, inclusion complexes of Sunset Yellow, Amaranth, Ponceau 4R, Carmoisine, Fast Red E, Tartrazine and Erythrosine with-CD were prepared. The formation of inclusion complexes was established by, among other methods, UV, reflectance and X-ray diffraction techniques. The host-to-guest ratio was determined by a UV spectral method. The effect of inclusion with-CD on binary mixtures such as Raspberry Red, Tomato Red and Orange Red was also studied.     

Synthese von 4-Acetoxy-1-aryl-2-azetidinonen

The 4-carboxy-2-azetidinones1 a,1 b und1 c react with leadtetraacetate/pyridine to give the 4-acetoxy-1-aryl-2-azetidinones2 a, 2 b and2 c. Hydrogenolysis of2 a yields2 d.