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Bicyclic Alkenes (bicyclic + alkene)
Selected AbstractsPalladium-Catalyzed [2 + 2 + 2] Cocyclotrimerization of Benzynes with Bicyclic Alkenes: An Efficient Route to Anellated 9,10-Dihydrophenanthrene Derivatives and Polyaromatic Compounds.CHEMINFORM, Issue 15 2005Thiruvellore Thatai Jayanth Abstract For Abstract see ChemInform Abstract in Full Text. [source] Asymmetric Induction in Ruthenium-Catalyzed [2 + 2] Cycloadditions Between Bicyclic Alkenes and a Chiral Acetylenic Acyl Sultam.CHEMINFORM, Issue 21 2004Karine Villeneuve Abstract For Abstract see ChemInform Abstract in Full Text. [source] Asymmetric ruthenium-catalysed [2+2] cycloadditions between bicyclic alkenes and chiral aryl-substituted acetylenic acyl camphorsultam alkynesACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009Jordan D. Goodreid The regio- and absolute stereochemistry of (7S)- N -[4-(3-thienyl)tricyclo[4.2.1.02,5]non-3-en-3-ylcarbonyl]-2,10-camphorsultam tetrahydrofuran hemisolvate, C24H29NO3S2·0.5C4H8O, and (7S)- N -[4-(4-tolyl)tricyclo[4.2.1.02,5]non-3-en-3-ylcarbonyl]-2,10-camphorsultam, C27H33NO3S, have been established. One contains a half-occupancy tetrahydrofuran solvent molecule located on a twofold axis and the other contains two crystallographically unique molecules which are nearly identical. The extended structures of both complexes can be explained via weak C,H...O interactions, which link the molecules together into two-dimensional sheets in the ab plane for the thienyl complex and ultimately into a three-dimensional structure for the tolyl derivative. The stereochemistry of both structures confirms that [2+2] cycloadditions of bicyclic alkenes and alkynes catalysed by ruthenium are exclusively exo. [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] | ||||||||||