Domino Knoevenagel hetero-Diels-Alder reactions: a stereoselective synthesis of sugar fused furo[3,2-b]pyrano[4,3-d]pyran derivatives

The O-prenyl derivative of a sugar aldehyde derived from d-glucose undergoes smooth intramolecular domino Knoevenagel hetero-Diels-Alder reactions with 1,3-diones to afford a novel class of carbohydrate analogues, cis-fused furopyranopyrans in good yields with a high degree of chemoselectivity. The stereochemistry of the products was assigned by NMR.     

Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.     

Uncatalyzed chemical oscillations in the aqueous acidic bromate oxidation of veratraldehyde

Oscillatory behavior in the uncatalyzed aqueous acidic bromate oxidation of 3,4-dimethoxybenzaldehyde (veratraldehyde) is reported. The generally used H₂SO₄ can be substituted by HNO₃, HClO₄, CCl₃ COOH and H₃PO₄ in this system. The length of the induction period is found to be dependent on the initial concentrations of the reagents and this effect is more prominent in the case of acidity. The precipitate accumulated in the reaction during oscillations has been identified. A plausible mechanism is also suggested. Experiments with allyl alcohol, a bromine scavenger, suggest that elemental bromine formed in the reaction has a role in the mechanism together with or besides bromide inons.

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3,4- () . H₂SO₄ HNO₃, HClO₄, CCl₃ COOH H₃PO₄ . . , , . . , , , , , .

     

Kinetics of thermal decomposition of trivalent metal complexes with all-cis-1,2,3,4-cyclopentane tetracarboxylic acid

All-cis-1, 2, 3, 4-cyclopentane tetracarboxylic acid forms 11 complexes with metals like Al(III), Y(III) and Ga(III), and have been isolated in solid state from the aqueous solutions. Thermogravimetry of these complexes supports the probable formulae assigned on the basis of elemental analysis. Kinetics of some of the thermal decompositions have been studied. Various kinetic parameters such as apparent activation energy, order of decomposition, frequency factor and activation entropy have been evaluated and the former two constants have been compared by two methods and are in reasonable agreement with each other.

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Zusammenfassung All-cis-l,2,3,4-Cyclopentantetracarbonsäure bildet 11 Komplexe mit Metallen wie Al(III), Y(III) und Ga(III). Sie wurden in festem Zustand aus den wässerigen Lösungen isoliert. Die Thermogravimetrie dieser Komplexe unterstützt die wahrscheinlichen Formeln, welche den Verbindungen auf Grund der Elementaranalyse Zugeschrieben worden sind. Die Kinetik einiger dieser thermischen Zersetzungen wurde untersucht. Verschiedene kinetische Parameter, wie die scheinbare Aktivierungsenergie, die Ordnung der Zersetzung, der Frequenzfaktor und die Aktivierungsentropie wurden bewertet und die ersten beiden Konstanten mittels zweier Methoden verglichen und in guter Übereinstimmung mit einander gefunden.

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Résumé L'acide all-cis-l,2,3,4-cyclopentanetétracarboxylique forme des complexes 11 avec les métaux tels que Al(III), Y(III) et Ga(III) et a été isolé à l'état solide à partir des solutions aqueuses. La thermogravimétrie de ces complexes vient à l'appui des formules probables établies par l'analyse élémentaire. La cinétique de la décomposition thermique de plusieurs d'entre eux a été étudiée. Divers paramètres cinétiques comme l'énergie d'activation, l'ordre de la décomposition, le facteur de fréquence et l'entropie d'activation ont été évalués. La comparaison des deux premières constantes obtenues par deux méthodes différentes montre une très bonne concordance des valeurs.

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--1,2,3,4- 1(III), (III) Ga(III) 11, . , . . , , , , , .

     

Two new bromotyrosine-derived metabolites from the sponge Psammaplysilla purpurea

Two new bromotyrosine-derived metabolites (1, 2) have been isolated along with the known compounds 3,5-dibromo-4-methoxyphenylacetonitrile, 3-bromo-4-methoxyphenylacetonitrile, 3-bromo-4-hydroxyphenylacetonitrile, 1-hydroxyuracil, 1-methoxyhemibastadin 2, purpuramine H and a steroid 5alpha,8alpha-epidioxycholest-6-en-3beta-ol from the sponge Psammaplysilla purpurea. Compounds 1 and 2 were characterized by interpretation of their spectral data. The antibacterial activity of these compounds is summarized.     

Oscillatory behavior in the oxidation of hematoxylin with bromate and sulfuric acid

Uncatalyzed and catalyzed oscillatory behavior in the redox potential in the oxidation of hematoxylin with acidic (H₂SO₄) bromate is reported.

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- (H₂SO₄) .

     

Concomitant polymorphs of 2,2',6,6'-tetramethyl-4,4'-terphenyldiol: the beta-quinol network reproduced in a metastable polymorph

The striking resemblance of the rhombohedral and monoclinic forms of the title molecule to beta- and gamma-quinol provides a crystal engineering approach to new polymorphic systems.     

CeCl3·7H2O Catalyzed,Microwave-Assisted High-Yield Synthesis of α-Aminophosphonates and their Biological Studies

Abstract

A new class of diethyl(3,5-dibromo-4-hydroxyphenylamino) (substituted phenyl/heterocyclic) methylphosphonates 4(a–j) has been synthesized by one-pot three component simultaneous reaction (Kabachnik–Fields) of 4-amino-2,6-dibromophenol 1, substituted heterocyclic/phenyl aldehydes 2(a–j), and diethylphosphite 3 using a Lewis acid catalyst, CeCl₃·7H₂O (5 mol%) under microwave irradiation as well as conventional conditions. It was observed that microwave irradiation method is more facile, efficient, and advantageous with respect to reaction time and yields. The structures of all the synthesized compounds were supported by analyzing IR, ¹H/¹³C/³¹P NMR, and mass spectral data. The synthesized compounds were screened for their in vitro antimicrobial and antioxidant activities.