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Stereoselective Construction (stereoselective + construction)
Selected AbstractsStereoselective Construction of a Highly Functionalized Taxoid ABC-Ring System: the C2,C9 Oxa-Bridge ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2005Sylvain Hamon Abstract The goal of this investigation is to assemble the 20-carbon unit 1 of the taxoid diterpene skeleton with a high level of stereocontrol by means of a three-reaction sequence developed in this laboratory. The strategy involves seven C,C bond-forming operations together with eighteen functional group transformations, circumventing the stereoselectivity issue altogether. Furthermore, there is no isomer formation and hence no need for chromatographic separation. A temporary oxa-bridge (C2/C9) was used as a problem-solving approach. The key step in the planned sequence was based on achieving the last C,C bonding between C11 and C12, following a successful C11 functionalization. X-ray analyses of 8b, 17, 18, 19, 20, and 21, together with extensive use of 800 MHz 1H (200 MHz 13C) NMR spectra, support the suggested structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Complete Regio- and Stereoselective Construction of Highly Substituted Silyl Enol Ethers by Three-Component Coupling,ANGEWANDTE CHEMIE, Issue 39 2010Dr. Akira Tsubouchi Drei Komponenten zur totalen Kontrolle: Dreifach substituierte Silylenolether wurden durch Dreikomponentenkupplung von ,,,-ungesättigten ,-Silylketonen, Organokupferreagentien und organischen Halogeniden vollständig regio- und stereoselektiv synthetisiert (siehe Schema). Die Reaktion verläuft über eine 1,3-Wanderung der Silylgruppe unter Bildung von cyclischen Silicat-Zwischenstufen, die die Konfiguration der Silylenolether festlegen. [source] A Concise Formal Synthesis of Diazonamide,A by the Stereoselective Construction of the C10 Quaternary Center,ANGEWANDTE CHEMIE, Issue 13 2010Cheng-Kang Mai Schutzgruppen überschätzt! Der Schlüsselschritt einer formalen Totalsynthese von Diazonamid,A ist die intramolekulare SNAr-Reaktion zwischen einem Oxindol und einem Bromoxazol. Interessanterweise verläuft diese Reaktion am besten, wenn das Oxindol-Stickstoffatom und die Phenolgruppe der Cyclisierungsvorstufe keine Schutzgruppen tragen und die milde Base Na2CO3 eingesetzt wird. [source] ChemInform Abstract: Stereoselective Construction of Halogenated Quaternary Stereogenic Centers via Catalytic Asymmetric Diels,Alder Reaction.CHEMINFORM, Issue 35 2010Kazutaka Shibatomi No abstract is available for this article. [source] ChemInform Abstract: CuX2 -Mediated [4 + 2] Benzannulation as a New Synthetic Tool for Stereoselective Construction of Haloaromatic Compounds.CHEMINFORM, Issue 6 2010Yukie Isogai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] ChemInform Abstract: Rhodium-Catalyzed Intramolecular Conjugate Addition of Vinylstannanes to Dihydro-4-pyridones: A Simple Method for Stereoselective Construction of 1-Azabicyclic Alkaloids.CHEMINFORM, Issue 40 2008Bartlomiej Furman 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] ChemInform Abstract: Stereoselective Construction of Nitrile-Substituted CyclopropanesCHEMINFORM, Issue 28 2008Justin R. Denton 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] Stereoselective Construction of BC-Ring Unit of 19-Hydroxytaxol by Samarium(II) Iodide-Mediated Double Aldol Cyclization.CHEMINFORM, Issue 30 2004Jun-ichi Matsuo No abstract is available for this article. [source] Diastereoselective Alkylation and Reduction of ,-Alkoxyacylsilanes: Stereoselective Construction of Three Contiguous Stereogenic Centers.CHEMINFORM, Issue 6 2004Mitsunori Honda Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Stereoselective Construction of Eight-Membered Carbocycles by Brook Rearrangement-Mediated [3 + 4] Annulation.CHEMINFORM, Issue 36 2002Kei Takeda Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] ChemInform Abstract: Zinc Bromide as Catalyst for the Stereoselective Construction of Quaternary Carbon: Improved Synthesis of Diastereomerically Enriched Spirocyclic Diols.CHEMINFORM, Issue 13 2001Yong Qiang Tu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Cobalt(diamine)-Catalyzed Cross-Coupling Reaction of Alkyl Halides with Arylmagnesium Reagents: Stereoselective Constructions of Arylated Asymmetric Carbons and Application to Total Synthesis of AH13205.CHEMINFORM, Issue 24 2006Hirohisa Ohmiya 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, please click on HTML or PDF. [source] Cobalt(diamine)-Catalyzed Cross-Coupling Reaction of Alkyl Halides with Arylmagnesium Reagents: Stereoselective Constructions of Arylated Asymmetric Carbons and Application to Total Synthesis of AH13205.CHEMINFORM, Issue 24 2006Hirohisa Ohmiya 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, please click on HTML or PDF. [source] Enantioselective Synthesis of 4-(Dimethylamino)pyridines through a Chemical Oxidation-Enzymatic Reduction Sequence.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2006Application in Asymmetric Catalysis Abstract Enantiomerically pure 4-(dimethylamino)-3-(1-hydroxyalkyl)pyridines and 4-(dimethylamino)-3-[hydroxy(phenyl)methyl]pyridine have been prepared through efficient chemoenzymatic routes. For this purpose different lipases and oxidoreductases have been tested in the preparation of optically active 4-chloro derivatives and baker's yeast was found to be an excellent catalyst for the bioreductions of the corresponding ketones. Their applications as enantioselective nucleophilic catalysts have been studied, important catalytic properties were observed in the stereoselective construction of quaternary centers. [source] Total Synthesis of (+)-Batzelladine A and (,)-Batzelladine D, and Identification of Their Target ProteinCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2005Jun Shimokawa Abstract Asymmetric total synthesis of batzelladine A (1) and batzelladine D (2) has been achieved. Our synthesis of batzelladines features 1) stereoselective construction of the cyclic guanidine system by means of successive 1,3-dipolar cycloaddition reaction and subsequent cyclization, 2) direct esterification of the bicyclic carboxylic acid 35 with the guanidine alcohol 8 or 59 to construct the whole carbon skeleton of batzelladines, and 3) one-step formation of the ,,,-unsaturated aldehyde 53 from the primary alcohol 47 with tetra- n -propylammoniumperruthenate (TPAP), providing an efficient route to the left-hand bicyclic guanidine alcohol of batzelladine A (1). With the synthetic compounds 1 and 2 in hand, their target protein was examined by using immobilized CD4 and gp120 affinity gels. The results indicated that batzelladines A (1) and D (2) bind specifically to CD4. [source] Studies on Stereoselective [2+2] Cycloadditions between N,N-Dialkylhydrazones and KetenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Eloísa Martín-Zamora Dr. Abstract Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the ,-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the ,-amino-,-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone. La reacción de cicloadición [2+2] de tipo Staudinger entre cetenas funcionalizadas y las hidrazonas quirales 1 constituye un método eficiente para la construcción estereoselectiva del anillo de azetidinona. La modulación de la estructura del grupo dialquilamino empleado como auxiliar, la disponibilidad de un procedimiento eficiente para la desprotección de las , -lactamas libres y la alta estabilidad química y térmica de las hidrazonas como N-dialquilamino iminas son los puntos clave para el éxito de la estrategia. Este último aspecto es de particular importancia por su implicación en la generalidad del método: hidrazonas derivadas de aldehídos fácilmente enolizables o incluso las derivadas de formaldehído reaccionan para dar lugar a los correspondientes cicloaductos con excelentes rendimientos químicos y estereoquímicos. La síntesis de los , -amino- , -hidroxiácidos (2R,3S)-fenilisoserina (42) y (2R,3S)-norestatina (45) se llevaron a cabo como ejemplos ilustrativos del potencial sintético del método. Estudios computacionales ab initio realizados sobre una reacción modelo basada en los auxiliares de la serie g sugieren un mecanismo en dos pasos a través de intermedios zwitteriónicos. Los resultados obtenidos explican la estereoquímica absoluta y relativa, así como el alto grado de inducción observado para estos auxiliares, por la preferencia de la aproximación "outward" de la cetena sobre la cara Re de la hidrazona. [source] | ||||||||||||||||||||||