Sample records for CICLIZACION (cyclization)

Sample records 1 - 10 shown.


Ultrasound-promoted formation of isopentenyl alcohol dianion: straightforward synthesis of perhydrofuro (2,3-b)furans

Alonso Valdés, Francisco; Rodríguez Fernández, María del Carmen; Sánchez Terrés, Daniel; Yus Astiz, Miguel

Ultrasound has been found to accelerate the formation of isopentenyl alcohol dianion by metalation with butyllithium in diethyl ether-tetrahydrofuran. The reaction of this dianion with carbonyl compounds followed by intramolecular acetalization under Wacker-type conditions provides a direct route fo...

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The biomimetic cyclization of melampomagnolide B

González, Antonio G.; Galindo, Antonio; Afonso, M. Mar; Mansilla, Horacio; López Rodríguez, Matías

5 pages, 2 figures, 2 schemes. | Supplementary material is obtainable on request from the Cambridge Crystallographic Data Centre (CCDC), University Chemical Laboratory, Lensfield Road, Cambridge. | Melampomagnolide B (9) was prepared and converted to the epimeric trans-(1αH,5βOH)-guaianolides (19) a...

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Sequential Norrish type II photoelimination and intramolecular aldol cyclization of 1,2-diketones in carbohydrate systems: stereoselective synthesis of cyclopentitols

Álvarez-Dorta, Dimitri; León, Elisa I.; Kennedy, Alan R.; Riesco-Fagundo, Concepción; Suárez, Ernesto

3 pages, 1 table, 3 schemes.-- PMID: 18846532 [PubMed]. | Supporting information (33 pages) available at: | The photochemical behavior of 1,2-diketones differs considerably from that of monoketones and has received a great deal of attenti...

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Involvement of NADPH in the cyclization reaction of carotenoid biosynthesis

Hornero Méndez, Dámaso; Britton, G.

PostdoctoralMarie Curie EU fellowship (FMBI-CT95-0450). | Cyclic carotenoids, e.g. L-carotene, are formed bycyclization of an acyclic precursor, lycopene. The gene, crtY,which encodes lycopene L-cyclase, has a partial sequencecharacteristic of a pyridine nucleotide binding domain, andNAD(P)H ha...

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Intramolecular hydrogen abstraction promoted by amidyl radicals. Evidence for electronic factors in the nucleophilic cyclization of ambident amides to oxocarbenium ions

Martín, Ángeles; Pérez Martín, Inés; Suárez, Ernesto

4 pages, 1 table, 1 scheme.-- PMID: 15876046 [PubMed].-- Printed version published May 12, 2005. | Supporting information available: Detailed experimental procedures and spectral and analytical data for compounds 1-16, 19, and precursors.-- Available at:

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A. Rojas, Hugo; Borda, Gloria del Carmen; Reyes, Patricio; Martínez, José J; Valencia, Jesús S; García-Fierro, José L

Resumen en portugués Nesse trabalho, foi estudada a hidrogenação seletiva do citronelal em catalisadores Ir/TiO2, Ir/SiO2 e Ir suportado em óxidos mistos (Ir/TiO2-SiO2) reduzidos a 473 e 773 K. Foi analisado o efeito da adição da TiO2 no suporte e das temperaturas de redução dos catalisadores para evaliar o possível efeito das espécies TiOx parcialmente reduzidas, sobre a atividade e seletividade da reação. Os sólidos resultantes foram caracterizados por quimisorção de hidrogên (mas) io a temperatura ambiente, adsorção de nitrogênio a 77 K, DRX, TEM e XPS. Os resultados indican que os catalisadores reduzidos a alta temperatura (HT: 773 K) favorecem a produção do álcool insaturado pelo efeito da interação forte metal-suporte conhecido como SMSI. Os catalisadores reduzidos a baixa temperatura (LT: 473 K) conduzen para a ciclização do anel produzindo isopulegol. Esses catalisadores mostraram uma alta atividade e uma baixa seletividade para álcool insaturado. Resumen en español En este trabajo se estudió la hidrogenación selectiva de citronelal sobre sistemas de Ir/TiO2, Ir/SiO2, e Ir soportado en óxidos mixtos (Ir/TiO2-SiO2) reducidos a 473 y 773 K. Se analizó el efecto de la adición de TiO2 al soporte y de las temperaturas de reducción de los catalizadores para evaluar el posible efecto de especies TiOx parcialmente reducidas, sobre la actividad y selectividad de la reacción. Los sólidos resultantes se caracterizaron por quimisorción (mas) de hidrógeno a temperatura ambiente, adsorción de nitrógeno a 77 K, DRX, TEM y XPS. Los resultados indican que los catalizadores reducidos a alta temperatura (HT: 773 K) favorecen la producción del alcohol insaturado debido al efecto de interacción fuerte metal-soporte conocido como SMSI. Los catalizadores reducidos a baja temperatura (LT: 473 K) llevan a la ciclización del anillo produciendo isopulegol. Estos catalizadores mostraron una alta actividad y una menor selectividad hacia el alcohol insaturado. Resumen en inglés Catalytic hydrogenation of citronellal over Ir/TiO2, Ir/SiO2, and Ir supported on mixed oxides (Ir/TiO2/SiO2) reduced at 473 y 773 K was studied. The effects of the partially reducible support species, the reduction temperatures (473 K or 773 K) and the successive TiO2 addition were analyzed. The catalysts were characterized by H2 chemisorption at room temperature, N2 adsorption at 77 K, XRD, TEM and XPS. The results showed that the high temperature reduction treatment (H (mas) T: 773 K) favored the production of the unsaturated alcohol, which can be explained in terms of the so-called strong metalsupport interaction (SMSI) effect. Catalysts reduced at low temperature (LT: 473 K) mainly led to a cyclization reaction producing isopulegol. These catalysts showed high activity but low selectivity to the unsaturated alcohol.

Scientific Electronic Library Online (Spanish)


Energetics and Geometry of FtsZ Polymers: Nucleated Self-Assembly of Single Protofilaments

Huecas, Sonia; Llorca, Óscar; Boskovic, Jasminka; Martín-Benito, Jaime; Valpuesta, José M.; Andreu, José Manuel

11 pages, 5 figures.-- PMID: 18024502 [PubMed].-- Data Supplement available (6 pages, 10 figures). | Essential cell division protein FtsZ is an assembling GTPase which directs the cytokinetic ring formation in dividing bacterial cells. FtsZ shares the structural fold of eukaryotic tubulin and assemb...

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Acid cyclization of 5-ketogermacren-6,12-olides. A reactivity and conformational study

Afonso, M. Mar; Mansilla, Horacio; Palenzuela, José A.; Galindo, Antonio

14 pages, 6 figures, 1 table, 4 schemes. | The acid cyclization of three related 5-ketogermacren-6,12-olides has been studied. All products have been identified and their stereochemistries established. The conformation of the germacrenolides and of the protonated derivatives have been studied in ord...

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