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Cyclization Leading (cyclization + leading)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

ChemInform Abstract: Reduction of Nitroarenes Followed by Propanol Group Transfer from Tris(3-hydroxypropyl)amine and Cyclization Leading to Quinolines under Heterogeneous Pd,C Catalysis.

CHEMINFORM, Issue 35 2010
Chan Sik Cho
No abstract is available for this article. [source]

ChemInform Abstract: Gold(I)-Catalyzed Hydroaminative Cyclization Leading to 2,5-Dihydroisoxazole.

CHEMINFORM, Issue 3 2008
Hyun-Suk Yeom
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Viscoelastic properties of polyacrylonitrile terpolymers during thermo-oxidative stabilization (cyclization)

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2008
K. I. Suresh
Abstract A study on the thermo-oxidative stabilization (cyclization) of polyacrylonitrile (PAN) terpolymers using dynamic mechanical thermal analysis (DMTA) is reported in this article. When the changes in viscoelastic properties were monitored in a rectangular tension mode, besides the tan , peak characteristic of the glass transition observed below 200°C, the copolymer and the terpolymer displayed a second peak above 200°C due to the cyclization leading to the formation of ladder structures. The initiation temperature of the cyclization process as well as the peak temperature is found to depend on the acid value and the composition of the precursor polymer. The results presented show that monitoring the changes in viscoelastic properties during cyclization provides insight into the material properties as a result of the chemical changes that are taking place. These observations were confirmed by structural characterization using IR spectroscopy, and the observed chemical changes agree with the literature studies, as due to the thermal cyclization process. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Lewis Acid-Assisted Ene Cyclization of 2-Azetidinone-Tethered Enals: Synthesis of Enantiopure Carbacepham Derivatives

CHEMISTRY - AN ASIAN JOURNAL, Issue 10 2009
Benito Alcaide Prof.
Abstract Diastereocontrolled Lewis acid-catalyzed preparation of enantiopure carbacepham derivatives have been developed starting from 2-azetidinone-tethered enals. The BF3,Et2O-promoted reaction of alkenylaldehydes 1 and 16 is effective as carbocyclization protocol to afford 4-substituted 5-hydroxycarbacephams or 3-substituted 4,5-dihydroxycarbacephams, respectively, by a type I carbonyl-ene reaction, while the BF3,Et2O or SnCl4 -mediated type II carbonyl-ene cyclization of alkenylaldehydes 2 furnishes 3-methylene 5-hydroxycarbacephams along with the corresponding 3-halo 5-hydroxycarbacepham. The stereochemical outcome of these carbonyl-ene cyclizations leading to carbacepham derivatives can be explained in terms of six-membered, cyclic chair-like transition-state models. The formation of halocarbacepham derivatives is proposed to proceed by a stepwise mechanism. Se ha desarrollado una nueva metodología sintética a sistemas ,-lactámicos bicíclicos basada en ciclaciones oxoénicas de los tipos I y II catalizadas por ácidos de Lewis de diferentes alquenil-4-oxoazetidin-2-carbaldehídos. De esta forma, se ha podido acceder, de manera sencilla y diastereoselectiva, a sistemas de carbacefam funcionalizados en forma ópticamente pura. De interés particular resultan los 2-metoxicarbonil-5-hidroxicarbacefams, ya que la presencia de un grupo carbonilo contiguo al nitrógeno ,-lactámico en los sistemas bicíclicos es un requisito fundamental para la actividad biológica de los antibióticos ,-lactámicos. En las ciclaciones oxoénicas de tipo I se ha observado una fuerte influencia de la estereoquímica del aldehido ,-lactámico de partida sobre la estereoselectividad de la reacción, siendo total para los aldehidos cis y baja o moderada para los isómeros trans. En las ciclaciones oxoénicas de tipo II de diferentes aldehidos ,-lactámicos, utilizando tanto SnCl4 como BF3.Et2O como catalizador, junto con los hidroxi-metilencarbacefams esperados, se han obtenido, en casi todos los casos, los correspondientes 3-cloro- o 3-fluorocarbacefams, en proporción variable dependiendo del catalizador utilizado. Este comportamiento, descrito para ácidos de Lewis tales como Me2AlCl o TiCl4, es desconocido para los ácidos de Lewis utilizados por nosotros. [source]