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Asymmetric Version (asymmetric + version)
Selected AbstractsA One-Pot Synthesis of Doubly Unsaturated Trifluoromethyl Amines:Easy Access to CF3 -Substituted PiperidinesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2005Guillaume Magueur Abstract A straightforward route to trifluoromethyl analogs of piperidines is described. These syntheses involve a Barbier-type allylation reaction of trifluoroacetaldimines, followed by N -allylation (one-pot), and ring-closing metathesis. An efficient asymmetric version is also reported (>98,% de). Functionalized heterobicyclic compounds can also be obtained by a Pauson,Khand reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Optimality for the linear quadratic non-Gaussian problem via the asymmetric Kalman filterINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2004Rosario Romera Abstract In the linear non-Gaussian case, the classical solution of the linear quadratic Gaussian (LQG) control problem is known to provide the best solution in the class of linear transformations of the plant output if optimality refers to classical least-squares minimization criteria. In this paper, the adaptive linear quadratic control problem is solved with optimality based on asymmetric least-squares approach, which includes least-squares criteria as a special case. Our main result gives explicit solutions for this optimal quadratic control problem for partially observable dynamic linear systems with asymmetric observation errors. The main difficulty is to find the optimal state estimate. For this purpose, an asymmetric version of the Kalman filter based on asymmetric least-squares estimation is used. We illustrate the applicability of our approach with numerical results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Catalytic Asymmetric Intramolecular Cascade Reaction for the Construction of Functionalized Benzobicyclo[4.3.0] Skeletons.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Remote Control of Enantioselectivity Abstract A catalytic asymmetric version of the intramolecular ylide annulation has been developed which affords high ee values and diastereoselectivities and which further shows that spirobiindane-based chiral phosphines can be excellent organocatalysts. Both optically active benzobicyclo[4.3.0] compounds 2 and 2, with three continuous stereogenic centers could be obtained as major products selectively under neutral and mild conditions just by a choice of an additive. [source] Phase-Transfer-Catalyzed Olefin Isomerization/,-Alkylation of ,-Alkynylcrotonates as a Route for 1,4-EnynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Takuya Hashimoto Abstract The phase-transfer-catalyzed alkylation of ,-alkynylcrotonates was developed as a means to provide 1,4-enynes deconjugated by an all-carbon quaternary center. Extension to the asymmetric version using the chiral phase-transfer catalyst (S)- 3 provided the alkylated compounds with up to 87% ee. [source] Asymmetric Total Synthesis of Fredericamycin A: An Intramolecular Cycloaddition PathwayCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Shuji Akai Dr. Abstract The asymmetric total synthesis of the potent antitumor antibiotic fredericamycin A ((S)- 1) was achieved by the intramolecular [4+2] cycloaddition of the silylene-protected styrene derivative (S)- 7 followed by the aromatic Pummerer-type reaction of the sulfoxide (S)- 5. Although we had already succeeded in the total synthesis of racemic 1 by the same approach, synthesis of its asymmetric version was more complicated than we had expected due to the difficulties involved in constructing the quaternary carbon center and the tendency of this center to undergo facile racemization. Racemization of this center during the installation of the acetylene moiety on the dione (R)- 8 was the most serious aspect. Systematic studies of its DE-ring analogue (R)- 25 revealed that racemization of the quaternary carbon center proceeded by a retro-aldol,aldol reaction of the initial adduct, (1R)- 39,a -Li, and that the degree of racemization was dependent on the reaction temperature. The racemization process could be completely depressed by keeping the reaction temperature at ,78,°C. The construction of the stereogenic quaternary carbon center was achieved by the lipase-catalyzed desymmetrization of the prochiral 1,3-diol 9,a bearing the DEF-ring moiety. These studies enabled us to attain the asymmetric total synthesis of (S)- 1 while completely retaining the chiral integrity created by the enzymatic reactions. [source] Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson,Khand Reactions: Applications to the Enantioselective Synthesis of Natural CyclopentanoidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004Marta Rodríguez Rivero Abstract The use of sulfoxides as chiral auxiliaries in asymmetric intermolecular Pauson,Khand reactions is described. After screening a wide variety of substituents on the sulfur atom in ,,,-unsaturated sulfoxides, the readily available o -(N,N -dimethylamino)phenyl vinyl sulfoxide (1,i) has proved to be highly reactive with substituted terminal alkynes under N -oxide-promoted conditions (CH3CN, 0,°C). In addition, these Pauson,Khand reactions occurred with complete regioselectivity and very high diastereoselectivity (de=86,>96,%, (S,RS) diastereomer). Experimental studies suggest that the high reactivity exhibited by the vinyl sulfoxide 1,i relies on the ability of the amine group to act as a soft ligand on the alkyne dicobalt complex prior to the generation of the cobaltacycle intermediate. On the other hand, both theoretical and experimental studies show that the high stereoselectivity of the process is due to the easy thermodynamic epimerization at the C5 center in the resulting 5-sulfinyl-2-cyclopentenone adducts. When it is taken into account that the known asymmetric intermolecular Pauson,Khand reactions are limited to the use of highly reactive bicyclic alkenes, mainly norbornene and norbornadiene, this novel procedure constitutes the first asymmetric version with unstrained acyclic alkenes. As a demonstration of the synthetic interest of this sulfoxide-based methodology in the enantioselective preparation of stereochemically complex cyclopentanoids, we have developed very short and efficient syntheses of the antibiotic (,)-pentenomycin I and the (,)-aminocyclopentitol moiety of a hopane triterpenoid. Se ha estudiado la utilización de sulfóxidos como auxiliares quirales en reacciones de Pauson,Khand intermoleculares. Tras considerar una amplia variedad de vinil sulfóxidos diferentemente sustituidos en el átomo de azufre, se ha encontrado que el o -(N,N -dimetilamino)fenil sulfóxido (1,i) presenta una elevada reactividad frente a alquinos terminales en reacciones de Pauson,Khand. Además, estas reacciones transcurren con regioselectividades completas y diastereoselectividades muy elevadas (ed=86,>96,%). Estudios teóricos y experimentales sugieren que la gran reactividad mostrada por el vinil sulfóxido 1,i se debe a la capacidad del grupo amino para coordinarse al complejo de dicobalto del alquino, favoreciendo así la posterior formación del cobaltaciclo intermedio. Por otro lado, estudios tanto teóricos como experimentales han demostrado que la elevada diastereoselectividad del proceso es consecuencia de la fácil epimerización termodinámica en la posición C-5 de las 5-sulfinil-2-ciclopentenonas finales. Teniendo en cuenta que hasta el momento la reacción de Pauson,Khand intermolecular estaba limitada al empleo de alquenos bicíclicos muy reactivos, principalmente norborneno y norbornadieno, este nuevo procedimiento constituye la primera versión asimétrica con alquenos acíclicos no tensionados. Como demostración de la utilidad sintética de esta nueva metodología en la preparación enantioselectiva de sistemas ciclopentánicos complejos, se han desarrollado síntesis muy eficaces del antibiótico (,)-pentenomicina I y de la unidad de aminociclopentitol de un triperpenoide. [source] | ||||||||||