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Khand Reaction (khand + reaction)
Selected AbstractsPauson,Khand Reaction of Allenic Hydrocarbons: Synthesis of 4-AlkylidenecyclopentenonesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2010Frédéric Antras Abstract The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4-alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio- and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results provide evidence that both initial pseudo-equatorial and pseudo-axial coordination modes of the allenic hydrocarbons onto one of the cobalt atoms of the primary alkyne,dicobalt complex are involved. DFT calculations supporting both these coordination modes are given. [source] ChemInform Abstract: Rh(I)-Catalyzed [(3 + 2) + 1] Cycloaddition of 1-Yne/Ene-vinylcyclopropanes and CO: Homologous Pauson,Khand Reaction and Total Synthesis of (.+-.)-,-Agarofuran (XIII).CHEMINFORM, Issue 41 2010Lei Jiao Abstract The novel reaction is developed to prepare bicyclic cyclohexanone derivatives. [source] ChemInform Abstract: A Hetero Pauson,Khand Reaction of Ketenimines: A New Synthetic Method for ,-Exomethylene-,,,-unsaturated ,-Lactams.CHEMINFORM, Issue 21 2010Takao Saito 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: The Pauson,Khand Reaction as a New Entry to the Synthesis of Bridged Bicyclic Heterocycles: Application to the Enantioselective Total Synthesis of (-)-Alstonerine (X).CHEMINFORM, Issue 7 2009Kenneth A. Miller 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: Synthesis of Tris(N,N-dimethylthiocarbamoyl)-1,1,1-tris-(methylaminomethyl)ethane and Its Application as Ligand for Pauson,Khand Reaction.CHEMINFORM, Issue 5 2009Zeljko Petrovski 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: A Sub-Stoichiometric Tungsten-Mediated Pauson,Khand Reaction: Scope and Limitations.CHEMINFORM, Issue 2 2009Patricia Garcia-Garcia 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] Rh(I)-Catalyzed Pauson,Khand Reaction of 1-Phenylsulfonyl-1,2-octadien-7-yne Derivatives.CHEMINFORM, Issue 37 2007Fuyuhiko Inagaki 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] Rh(I)-Catalyzed Allenic Pauson,Khand Reaction: First Construction of the Bicyclo[6.3.0]undecadienone Ring System.CHEMINFORM, Issue 7 2006Chisato Mukai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF. [source] A Cyclobutadiene Equivalent in the Catalytic Pauson,Khand Reaction.CHEMINFORM, Issue 6 2005Susan E. Gibson Abstract For Abstract see ChemInform Abstract in Full Text. [source] Catalytic Activity of Dodecarbonyltetracobalt in Aqueous Media: A "Greening" of the Pauson,Khand Reaction.CHEMINFORM, Issue 48 2004Llorente V. R. Bonaga Abstract For Abstract see ChemInform Abstract in Full Text. [source] Investigation of Intramolecular Pauson,Khand Reaction of 2-Aryl-1,6- and 1-Methyl-1,7-enynes (exo-Olefins) and 1-Phenyl-1-octen-7-yne (endo-Olefin).CHEMINFORM, Issue 29 2004Miyuki Ishizaki Abstract For Abstract see ChemInform Abstract in Full Text. [source] Asymmetric Synthesis of Fused Bicyclic ,-Amino Acids Having a Hexahydro-cyclopenta[c]pyridine Skeleton via Intramolecular Pauson,Khand Reaction of 1-Sulfonimidoyl-Substituted 5-Azaoct-1-en-7-ynes.CHEMINFORM, Issue 8 2004Markus Guenter Abstract For Abstract see ChemInform Abstract in Full Text. [source] Trimethylgermyl Group in Pauson,Khand Reaction.CHEMINFORM, Issue 6 2003Chisato Mukai Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Investigation of the Synthesis of Angular Tricyclic Compounds by Intramolecular Pauson,Khand Reaction of exo- and endo-Cyclic Enynes.CHEMINFORM, Issue 31 2001Miyuki Ishizaki 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: Dodecacarbonyltetracobalt Catalysis in the Thermal Pauson,Khand Reaction.CHEMINFORM, Issue 4 2001Marie E. Krafft 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] Steric Buttressing in the Pauson,Khand Reactions of Aryl Enynes.CHEMINFORM, Issue 37 2007Christian E. Madu 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] Intramolecular Pauson,Khand Reactions of Cycloheptynedicobalt Complexes.CHEMINFORM, Issue 46 2005Ahmed B. Mohamed Abstract For Abstract see ChemInform Abstract in Full Text. [source] The Exclusive Formation of Cyclopentenones from Molybdenum Hexacarbonyl-Catalyzed Pauson,Khand Reactions of 5-Allenyl-1-ynes.CHEMINFORM, Issue 39 2005Arun Kumar Gupta Abstract For Abstract see ChemInform Abstract in Full Text. [source] Inhibition of Enone Reduction in Aqueous-Phase Pauson,Khand Reactions.CHEMINFORM, Issue 22 2005Marie E. Krafft Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Intermolecular Pauson,Khand Reactions of Cyclopropene: A General Synthesis of Cyclopentanones.CHEMINFORM, Issue 8 2002Iolanda Marchueta 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] 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] 2,2,-Bis[bis(3,5-di- tert -butyl-4-methoxyphenyl)phosphino]-6,6,-dimethoxy-1,1,-biphenyl in Intramolecular Rhodium(I)-Catalyzed Asymmetric Pauson,Khand-Type ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Dong Eun Kim Abstract A cationic rhodium(I)/2,2,-bis[bis(3,5-di- tert -butyl-4-methoxyphenyl)phosphino]-6,6,-dimethoxy-1,1,-biphenyl (DTBM-MeO-BIPHEP) catalyst was highly efficient for the asymmetric catalytic Pauson,Khand reaction, especially for those substrates containing aryl group-substituted alkynes. The formation of the products that were derived from a ,-hydride eliminated intermediate 5 was completely suppressed over a wide range of substrates. This reaction was a serious process competing reaction with the migratory CO insertion that led to the Pauson,Khand reaction product and often substantially ruined the chemical yield of the Pauson,Khand reaction. The advantages of this system were clearly demonstrated for previously troublesome substrates, N -tosyl- (1b) and malonate-tethered 1,6-enynes (1c), that exhibited a higher enantioselectivity without a loss in the chemical yields. The obvious beneficial effects were attributed to the synergic effect of various factors, such as the electron density of the phosphorus of the ligand, the dihedral angles of the atropisomeric ligand, and the substitution on the phosphine aryl rings which play a crucial role in the stereochemical outcome of Rh-catalyzed Pauson,Khand reaction. [source] Three characteristic reactions of alkynes with metal compounds in organic synthesisAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2008Iwao Omae Abstract Alkynes have two sets of mutually orthogonal ,-bonds that are different from the ,-bonds of alkenes. These ,-bonds are able to bond with transition metal compounds. Alkynes easily bond with the various kinds of compounds having a ,-bond such as carbon monoxide, alkenes, other alkynes and nitriles in the presence of the transition metal compounds. The most representative reaction of alkynes is called the Pauson,Khand reaction. The Pauson,Khand reactions include the cyclization of alkynes with alkenes and carbon monoxide in the presence of cobalt carbonyls. Similar Pauson,Khand reactions also proceed in the presence of other transition metal compounds. These reactions are the first type of characteristic reaction of alkynes. Other various kinds of cyclizations with alkynes also proceed in the presence of the transition metal compounds. These reactions are the second type of characteristic reaction of alkynes. These include cyclooligomerizations and cycloadditions. The cyclooligomerizations include mainly cyclotrimerizations and cyclotetramerizations, and the cycloadditions are [2 + 2], [2 + 2 + 1], [2 + 2 + 2], [3 + 2], [4 + 2], etc., type cycloadditions. Alkynes are fairly reactive because of the high s character of their ,-bonds. Therefore, simple coupling reactions with alkynes also proceed besides the cyclizations. The coupling reactions are the third type of characteristic reactions of alkynes in the presence of, mainly, the transition metal compounds. These reactions include carbonylations, dioxycarbonylations, Sonogashira reactions, coupling reactions with aldehydes, ketones, alkynes, alkenes and allyl compounds. Copyright © 2008 John Wiley & Sons, Ltd. [source] Characteristic reactions of group 9 transition metal compounds in organic synthesisAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2009Iwao Omae Abstract Group 9 metal compounds in organic synthesis have two characteristic reactions. The first occurs because the group 9 metals have a high affinity to carbon,carbon or carbon,nitrogen ,-bonds. The first type of characteristic reactions in these group 9 metal compounds includes Pauson,Khand reactions, the Pauson,Khand-type reactions ([2 + 2 + 1] cyclization), the other cyclizations and coupling reactions. The second occurs because the group 9 metals have a high affinity to carbonyl groups. The second type of characteristic reactions includes carbonylations such as hydroformylations, the carbonylations of methanol, amidocarbonylations and other carbonylations. The first characteristic reactions are applied for the synthesis of fine chemicals such as pharmaceuticals and agrochemicals. However, the second characteristic reactions are utilized not only for fine chemicals but also for important bulk commodity chemicals such as aldehydes, carboxylic acids and alcohols. Copyright © 2009 John Wiley & Sons, Ltd. [source] Three characteristic reactions of alkynes with metal compounds in organic synthesisAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2008Iwao Omae Abstract Alkynes have two sets of mutually orthogonal ,-bonds that are different from the ,-bonds of alkenes. These ,-bonds are able to bond with transition metal compounds. Alkynes easily bond with the various kinds of compounds having a ,-bond such as carbon monoxide, alkenes, other alkynes and nitriles in the presence of the transition metal compounds. The most representative reaction of alkynes is called the Pauson,Khand reaction. The Pauson,Khand reactions include the cyclization of alkynes with alkenes and carbon monoxide in the presence of cobalt carbonyls. Similar Pauson,Khand reactions also proceed in the presence of other transition metal compounds. These reactions are the first type of characteristic reaction of alkynes. Other various kinds of cyclizations with alkynes also proceed in the presence of the transition metal compounds. These reactions are the second type of characteristic reaction of alkynes. These include cyclooligomerizations and cycloadditions. The cyclooligomerizations include mainly cyclotrimerizations and cyclotetramerizations, and the cycloadditions are [2 + 2], [2 + 2 + 1], [2 + 2 + 2], [3 + 2], [4 + 2], etc., type cycloadditions. Alkynes are fairly reactive because of the high s character of their ,-bonds. Therefore, simple coupling reactions with alkynes also proceed besides the cyclizations. The coupling reactions are the third type of characteristic reactions of alkynes in the presence of, mainly, the transition metal compounds. These reactions include carbonylations, dioxycarbonylations, Sonogashira reactions, coupling reactions with aldehydes, ketones, alkynes, alkenes and allyl compounds. Copyright © 2008 John Wiley & Sons, Ltd. [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] | ||||||||||