Methyl sulfinates as electrophiles in Friedel-Crafts reactions. Synthesis of aryl sulfoxides

The Friedel-Crafts reaction of methyl alkyl- and arylsulfinates with aromatic systems, activated by one or more electron-donating substituents (OH, OMe, NHR, NR(2)), provides alkyl aryl and diaryl sulfoxides under mild conditions and in moderate to good yields. The very high regioselectivity usually observed in these sulfinylation reactions is rationalized on the basis of a Wheland intermediate having a trigonal bypyramidal structure in which steric and electronic interactions are significant factors strongly destabilizing the attack to the ortho positions.     

A Simple Method to Prepare Alkyl 3,5-Dioxohexanoates

A simple and efficient method to prepare alkyl 3,5-dioxohexanoates by alcoholysis of isopropylidene (1-hydroxy-3-oxo-butylidene) malonate is described.     

Diferenciación de algunas diazinas

Résumé On décrit l'emploi d'une solution à 2% de phosphomolybdate comme réactif pour l'identification et la séparation de la pipérazine, de la pyrazine, de la pyridazine et de la pyrimidine par microcristallisations. Les produits de réaction obtenus rendent possibles la caractérisation et la séparation des diazines, d'après la forme et la couleur ainsi que la sensibilité de la réaction.

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Summary The use of 2% phosphomolydic solution for the identification and differentiation of piperazine, pyrazine, pyridazine, and pyrimidine through microcrystal precipitations is described. The products obtained permit the characterization and differentiation of the diazines by form and color or by the sensitivity of the reaction.

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Zusammenfassung Die Anwendung 2%iger Phosphormolybdänsäurelösung als Reagens zur Identifizierung und Unterscheidung von Piperazin, Pyrazin, Pyridazin und Pyrimidin durch Mikrokristallfällungen wird beschrieben. Die erhaltenen Reaktionsprodukte ermöglichen die Charakterisierung und Unterscheidung der Diazine nach Form und Farbe bzw. Empfindlichkeit der Reaktion.

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Resumen Se describe el uso del ácido fosfomolibdico en solutión al 2% como reactivo para caracterizar y diferenciar a la piperacina, pirazina, piridazina y pirimidina, desde el punto de vista microcristalino, por proporcionar reacciones que por sus formas, cromatismo y sensibilidades, permiten caracterizar y diferenciar a las diazinas en estudio.

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Dedicado a la ocasión del centésimo aniversario del nacimiento deFriedrich Emich.     

High‐temperature stability of suspended single‐layer graphene

We report in situ Joule heating on suspended single‐layer graphene in a transmission electron microscope (TEM). Thermally‐driven degradation of pre‐deposited nanoparticles on the membrane is monitored and used for local temperature estimation. By extrapolating the Joule heating power and temperature relation, we find that the suspended single‐layer graphene has exceptional thermal stability up to at least 2600 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the second Feng-Rao distance of Algebraic Geometry codes related to Arf semigroups

We describe the second (generalized) Feng-Rao distance for elements in an Arf numerical semigroup that are greater than or equal to the conductor of the semigroup. This provides a lower bound for the second Hamming weight for one point AG codes. In particular, we can obtain the second Feng-Rao distance for the codes defined by asymptotically good towers of function fields whose Weierstrass semigroups are inductive. In addition, we compute the second Feng-Rao number, and provide some examples and comparisons with previous results on this topic. These calculations rely on Apéry sets, and thus several results concerning Apéry sets of Arf semigroups are presented.     

Structural and spectral assignment of a new diterpenoid isolated from Ballota undulata and a complete (1)H and (13)C NMR data assignment for three other structurally related compounds

The structure of 3beta-hydroxyballotinone, a new labdane diterpenoid isolated from Ballota undulata, has been established by NMR spectroscopic studies. In addition, complete and unambiguous assignments of the (1)H and (13)C NMR spectra of three other already known labdanes (ballotinone, ballonigrin and ballonigrinone) isolated from the same source have been achieved. The assignments are based on 2D shift-correlated (1)H--(1)H COSY, (1)H--(13)C gHSQC [(1)J(C,H)] and (1)H--(13)C gHMBC [(n)J(C,H) (n = 2 and 3)], and NOE experiments.     

NMR and x-ray conformational study of artemisiifolin and three other related germacranolides

From an acetone extract of Staehelina dubia, large quantities of the previously known germacranolide artemisiifolin were isolated. The conformations of the 10-membered germacra-1(10)E,4Z-diene ring system of this compound and those of its derivatives 11,13-dihydroartemisiifolin, isabelin and 6alpha-hydroxy-15-oxogermacra-1(10)E,4Z,11(13)-trien-12,8alpha-olide were studied by NMR spectroscopic methods. Low-energy conformations were obtained by quantum mechanical calculations. An x-ray diffraction analysis of artemisiifolin established that, in the crystalline state, it possesses a unique conformation that corresponds to the majority one existing in acetone-d6 solution.     

Structural and spectral assignment of three forskolin-like diterpenoids isolated from Plectranthus ornatus

Three labdane diterpenoids were isolated from an acetone extract of Plectranthus ornatus. Their structures, closely related to that of forskolin, were determined by NMR studies. Unambiguous and complete assignments of the 1H and 13C NMR chemical shifts for these substances are presented. The assignments are based on 2D shift-correlated [1H, 1H-COSY, 1H, 13C-gHSQC-1J (C,H), 1H, 13C-gHMBC-(n)J (C,H) (n = 2 and 3)] and NOE experiments.     

Synthetic studies on neoclerodane diterpenes from Salvia splendens: oxidative modifications of ring A

Salvinorin A (1), a neoclerodane diterpene from the hallucinogenic mint Salvia divinorum, is the only known naturally occurring non-nitrogenous and specific κ-opioid agonist. Some oxidative modifications of the A ring in the congeners of 1 isolated from Salvia splendens salviarin, splenolide B, splendidin, and in the non-natural 8-epi-salviarin gave new derivatives, some of which were tested as agonists at opioid receptors. However, none of these compounds was active. The presence of the C-18, C-19 lactone could be at the origin of the observed lack of binding affinity.     

Characterization of Kaolin Glassy Carbon Modified Electrodes: Preconcentration of 2‐Chlorophenol

In this paper we describe the use of two kaolin‐type aluminosilicate clays, a commercial ceramic‐grade kaolin (K) and a natural kaolin from mines in Bolívar State Venezuela (K‐Ve), for the preparation of film‐based clay‐modified glassy carbon electrodes. We examine their behavior during the preconcentration and subsequent anodic oxidation of 2‐chlorophenol. Kaolin samples were used as raw materials and modified with cationic surfactant, cetyltrimethylammonium bromide (CTAB) or nonionic surfactant, octylphenoxypolyethoxyethanol (TX100). The electrode polishing was the key step to produce stable films. 2‐Chlorophenol electrooxidation is favored by the presence of the surfactants in the film. The X‐ray patterns show that the kaolin K‐Ve includes quartz as nonclay mineral, while the kaolin K showed only diffraction peaks characteristic of kaolinite phase. This may be why the TX100/K‐Ve/GC electrode adsorbs more 2‐CPh than the TX100/K/GC electrode. On the other hand, analysis of the limiting currents obtained from hydrodynamic techniques indicated that the permeability of TX100/kaolin films is greater than that of CTAB/kaolin films. The TX100/K‐Ve/GC electrode showed excellent stability. A linear response range from 0.01mgL^?1 up to 0.1 mg L^?1 with a detection limit of 0.0016 mg L^?1 was observed in the optimized conditions.