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Barry K Sharpless - One of the best experts on this subject based on the ideXlab platform.
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selective Asymmetric Dihydroxylation of polyenes
Tetrahedron, 1995Co-Authors: Heinrich Becker, Marcos A Soler, Barry K SharplessAbstract:Abstract The Asymmetric Dihydroxylation procedure (AD) is applied to a variety of polyenes. In many cases excellent regioselectivities are obtained. The observed selectivities are rationalized in terms of electronic and/or steric effects inherent to the substrate, superimposed on the substrate's favorable or unfavorable interactions with the binding pocket of the AD ligand. Surprisingly, for medium and large ring olefins with trans-double bonds outstanding enantioselectivities are realized using the pyrimidine ligands. A hexaol of D3 symmetry is prepared from all trans cyclododecatriene.
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Asymmetric Dihydroxylation of primary allylic halides and a concise synthesis of diepoxybutane
Tetrahedron Letters, 1994Co-Authors: Koen P M Vanhessche, Z M Wang, Barry K SharplessAbstract:Abstract The Asymmetric Dihydroxylation (AD) of primary allylic halides is described. Enantiomeric excesses range from 40 to 98%. Subsequent base treatment gives epoxy alcohols in high yields. This strategy is further illustrated by the synthesis of (−)-diepoxybutane, an important C 4 -chiral building block.
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toward an understanding of the high enantioselectivity in the osmium catalyzed Asymmetric Dihydroxylation ad 1 kinetics
Journal of the American Chemical Society, 1994Co-Authors: Hartmuth C Kolb, Pher G Andersson, Barry K SharplessAbstract:Toward an Understanding of the High Enantioselectivity in the Osmium-Catalyzed Asymmetric Dihydroxylation (AD). 1. Kinetics
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synthesis of optically active secondary allylic alcohols from allylsilanes via successive Asymmetric Dihydroxylation ad and peterson olefination reactions
Tetrahedron Letters, 1993Co-Authors: Barry K Sharpless, Fumie Sato, Sentaro Okamoto, Kousuke Tani, Davit ZargarianAbstract:Abstract Optically active, secondary allylic alcohols can be prepared from allylic silanes by the sucessive Asymmetric Dihydroxylation and Peterson olefination reactions. The Effects of trialkylsilyl groups on the outcome of the AD reaction on vinyl and allyl silanes are also discussed.
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syntheses and crystal structures of the cinchona alkaloid derivatives used as ligands in the osmium catalyzed Asymmetric Dihydroxylation of olefins
Journal of Organic Chemistry, 1993Co-Authors: Willi Amberg, Yasukazu Ogino, Gerard A Crispino, Jens Hartung, Tomoyuki Shibata, Youssef L Bennani, Kyu Sung Jeong, Raj K Chadha, William D Davis, Barry K SharplessAbstract:Experimental procedures for the preparation of two classes of derivatives of the cinchona alkaloids dihydroquinine and dihydroquinidine are described. Ligands (DHQ) 2 -PHAL, 1a, and (DHQD) 2 -PHAL, 2a, are conveniently synthesized in good yield by the reaction of the corresponding alkaloid with 1,4-dichlorophthalazine in the presence of K 2 CO 3 and KOH in refluxing toluene. Derivatives DHQ-PHN, 1b, and DHQD-PHN, 2b, are prepared through an Ullmann-type coupling between the 9-O-alkaloid sodium alkoxide and 9-iodophenanthrene in the presence of CuI and pyridine. Crystal structures for derivatives 2a and 2b are also presented. These four alkaloid derivatives serve as highly enantioselective ligands for the osmium tetraoxide catalyzed Asymmetric Dihydroxylation (AD) of olefins
Carlos A M Afonso - One of the best experts on this subject based on the ideXlab platform.
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sharpless Asymmetric Dihydroxylation of olefins in watersurfactant media with recycling of the catalytic system by membrane nanofiltration
Advanced Synthesis & Catalysis, 2008Co-Authors: Luis C Branco, Frederico Castelo Ferreira, J L C Santos, Joao G Crespo, Carlos A M AfonsoAbstract:This paper presents a new and more sustainable alternative approach for the Sharpless catalytic Asymmetric Dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric Dihydroxylation of 1-hexene in a 1.5 mM sodium cholate aqueous solution, using N-methylmorpholine N-oxide (NMO) as co-oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields.
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application of nanofiltration to re use the sharpless Asymmetric Dihydroxylation catalytic system
Tetrahedron-asymmetry, 2007Co-Authors: Luis C Branco, Frederico Castelo Ferreira, Joao G Crespo, Kaushal Kishor Verma, Carlos A M AfonsoAbstract:Abstract In this paper, successive batch steps of an osmium-catalyzed Asymmetric Dihydroxylation reaction using Sharpless conditions and nanofiltration of post-reaction mixture were coupled, allowing us to enhance the cumulative catalyst turn over number to about 3.7 times over six cycles. The nanofiltration step provides for isolation of the chiral product, whereas the catalytic system (osmium and chiral ligand) is re-used in the following batch cycle. In this work the osmium average rejection through the selected nanofiltration membrane, Starmem™120, was 83%; this result may indicate the existence of free osmium in solution and implies residual product osmium contamination at an average value of 1.5 mg Os/g-product. Effective application of this methodology to the model reaction requires improvement of catalyst rejection, which calls for an effective complexation of osmium by the ligand. Nevertheless, the enantioselectivity of the reaction was maintained constant over the six cycles at a value of 69%.
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osmium catalyzed Asymmetric Dihydroxylation of methyl trans cinnamate in ionic liquids followed by supercritical co2 product recovery
Journal of Organometallic Chemistry, 2005Co-Authors: Ana Serbanovic, Luis C Branco, Manuel Nunes Da Ponte, Carlos A M AfonsoAbstract:Abstract In this work, osmium-catalyzed Asymmetric Dihydroxylation (AD) of methyl trans -cinnamate was studied. Osmium and chiral ligand catalysts were immobilized in ionic liquid only, without any other reaction solvents, while the recovery of the product was performed by extraction with supercritical CO 2 , and compared with results obtained by extractions with organic solvents such as hexane and diethyl ether. In supercritical CO 2 extraction experiments, optimal extraction pressure was found and ionic liquid chosen, so that the highest reaction yields coupled with lowest osmium content in the crude product can be achieved. Finally, recycle experiments of the same (ionic liquid + catalytic system) mixture were successfully conducted. Application of ionic liquids and supercritical CO 2 in osmium catalyzed AD allows for the isolation of the diol basically without contamination with osmium, in high yield and enantiomeric excess, and it makes possible the efficient reuse of ionic liquid solvent and the catalytic system.
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ionic liquids as a convenient new medium for the catalytic Asymmetric Dihydroxylation of olefins using a recoverable and reusable osmium ligand
Journal of Organic Chemistry, 2004Co-Authors: Luis C Branco, Carlos A M AfonsoAbstract:The use of room-temperature ionic liquids (RTILs) in the Sharpless catalytic Asymmetric Dihydroxylation (AD) as a cosolvent or replacement of the tert-butanol was studied in detail by screening 11 different RTILs. The AD reaction is faster in 1-n-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] as a cosolvent than in the conventional system of tert-butanol/H2O. For the range of six substrates tested, comparable or even higher yields and enantiomeric excess (ee) were found using [C4mim][PF6] or 1-n-octyl-3-methylimidazolium hexafluorophosphate [C8mim][PF6] compared to the conventional solvent system. Due to high affinity of the catalytic osmium/quiral ligand system to the ionic liquid, the use of ionic liquid/water (biphasic) or ionic liquid/water/tert-butanol (monophasic) solvent systems provides a recoverable, reusable, robust, efficient, and simple system for the AD reaction. Using 1-hexene and [C4mim][PF6] as RTIL it was possible to reuse the catalytic system for 9 cycles with only a 5% of yi...
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catalytic Asymmetric Dihydroxylation of olefins using a recoverable and reusable oso42 in ionic liquid bmim pf6
ChemInform, 2003Co-Authors: Luis C Branco, Carlos A M AfonsoAbstract:The use of the solvent systems water/ionic liquid or water/ionic liquid/tert-butanol provides a recoverable, reusable, robust and simple system for the Asymmetric Dihydroxylation of olefins, based on the immobilization of the osmium-ligand catalyst in the ionic liquid phase
Luis C Branco - One of the best experts on this subject based on the ideXlab platform.
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sharpless Asymmetric Dihydroxylation of olefins in watersurfactant media with recycling of the catalytic system by membrane nanofiltration
Advanced Synthesis & Catalysis, 2008Co-Authors: Luis C Branco, Frederico Castelo Ferreira, J L C Santos, Joao G Crespo, Carlos A M AfonsoAbstract:This paper presents a new and more sustainable alternative approach for the Sharpless catalytic Asymmetric Dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric Dihydroxylation of 1-hexene in a 1.5 mM sodium cholate aqueous solution, using N-methylmorpholine N-oxide (NMO) as co-oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields.
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application of nanofiltration to re use the sharpless Asymmetric Dihydroxylation catalytic system
Tetrahedron-asymmetry, 2007Co-Authors: Luis C Branco, Frederico Castelo Ferreira, Joao G Crespo, Kaushal Kishor Verma, Carlos A M AfonsoAbstract:Abstract In this paper, successive batch steps of an osmium-catalyzed Asymmetric Dihydroxylation reaction using Sharpless conditions and nanofiltration of post-reaction mixture were coupled, allowing us to enhance the cumulative catalyst turn over number to about 3.7 times over six cycles. The nanofiltration step provides for isolation of the chiral product, whereas the catalytic system (osmium and chiral ligand) is re-used in the following batch cycle. In this work the osmium average rejection through the selected nanofiltration membrane, Starmem™120, was 83%; this result may indicate the existence of free osmium in solution and implies residual product osmium contamination at an average value of 1.5 mg Os/g-product. Effective application of this methodology to the model reaction requires improvement of catalyst rejection, which calls for an effective complexation of osmium by the ligand. Nevertheless, the enantioselectivity of the reaction was maintained constant over the six cycles at a value of 69%.
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osmium catalyzed Asymmetric Dihydroxylation of methyl trans cinnamate in ionic liquids followed by supercritical co2 product recovery
Journal of Organometallic Chemistry, 2005Co-Authors: Ana Serbanovic, Luis C Branco, Manuel Nunes Da Ponte, Carlos A M AfonsoAbstract:Abstract In this work, osmium-catalyzed Asymmetric Dihydroxylation (AD) of methyl trans -cinnamate was studied. Osmium and chiral ligand catalysts were immobilized in ionic liquid only, without any other reaction solvents, while the recovery of the product was performed by extraction with supercritical CO 2 , and compared with results obtained by extractions with organic solvents such as hexane and diethyl ether. In supercritical CO 2 extraction experiments, optimal extraction pressure was found and ionic liquid chosen, so that the highest reaction yields coupled with lowest osmium content in the crude product can be achieved. Finally, recycle experiments of the same (ionic liquid + catalytic system) mixture were successfully conducted. Application of ionic liquids and supercritical CO 2 in osmium catalyzed AD allows for the isolation of the diol basically without contamination with osmium, in high yield and enantiomeric excess, and it makes possible the efficient reuse of ionic liquid solvent and the catalytic system.
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ionic liquids as a convenient new medium for the catalytic Asymmetric Dihydroxylation of olefins using a recoverable and reusable osmium ligand
Journal of Organic Chemistry, 2004Co-Authors: Luis C Branco, Carlos A M AfonsoAbstract:The use of room-temperature ionic liquids (RTILs) in the Sharpless catalytic Asymmetric Dihydroxylation (AD) as a cosolvent or replacement of the tert-butanol was studied in detail by screening 11 different RTILs. The AD reaction is faster in 1-n-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] as a cosolvent than in the conventional system of tert-butanol/H2O. For the range of six substrates tested, comparable or even higher yields and enantiomeric excess (ee) were found using [C4mim][PF6] or 1-n-octyl-3-methylimidazolium hexafluorophosphate [C8mim][PF6] compared to the conventional solvent system. Due to high affinity of the catalytic osmium/quiral ligand system to the ionic liquid, the use of ionic liquid/water (biphasic) or ionic liquid/water/tert-butanol (monophasic) solvent systems provides a recoverable, reusable, robust, efficient, and simple system for the AD reaction. Using 1-hexene and [C4mim][PF6] as RTIL it was possible to reuse the catalytic system for 9 cycles with only a 5% of yi...
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catalytic Asymmetric Dihydroxylation of olefins using a recoverable and reusable oso42 in ionic liquid bmim pf6
ChemInform, 2003Co-Authors: Luis C Branco, Carlos A M AfonsoAbstract:The use of the solvent systems water/ionic liquid or water/ionic liquid/tert-butanol provides a recoverable, reusable, robust and simple system for the Asymmetric Dihydroxylation of olefins, based on the immobilization of the osmium-ligand catalyst in the ionic liquid phase
Kim D. Janda - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Dihydroxylation catalyzed by ionic polymer-supported osmium tetroxide
Tetrahedron Letters, 2005Co-Authors: Byoung Se Lee, Suresh Mahajan, Kim D. JandaAbstract:Abstract Osmium tetroxide was immobilized onto a short-length PEGylated ionic polymer, which exhibited excellent catalytic performance in OsO4-catalyzed Asymmetric Dihydroxylation. The resulting polymer was recycled five times without any loss of yield or enantioselectivity. In addition to the immobilization of osmium, the polymer also exhibited an ability to immobilize a significant amount of chiral ligand.
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a soluble polymer bound approach to the sharpless catalytic Asymmetric Dihydroxylation ad reaction preparation and application of a dhqd 2phal peg ome ligand
Tetrahedron Letters, 1997Co-Authors: Hyunsoo Han, Kim D. JandaAbstract:Abstract The synthesis of a soluble polymer-bound (DHQD)2PHAL ligand 1 and its successful application in the catalytic Asymmetric Dihydroxylation reaction are described. The results highlight that the soluble polymer-bound ligand approach offers all the benefits associated with insoluble supports but with the key advantages of increased reactivity and enantioselectivity inherent with solution-phase methodology.
Choong Eui Song - One of the best experts on this subject based on the ideXlab platform.
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markedly enhanced recyclability of osmium catalyst in Asymmetric Dihydroxylation reactions by using macroporous resins bearing both residual vinyl groups and quaternary ammonium moieties
ChemInform, 2005Co-Authors: Kwang Jin Kim, Eun Kyung Kwueon, Doo Seong Choi, Han Young Choi, Soon Ho Hwang, Yil Sung Park, Choong Eui SongAbstract:Markedly enhanced recyclability of osmium catalyst in Asymmetric Dihydroxylation has been achieved by using osmylated macroporous resins bearing both residual vinyl groups and quaternary ammonium moiety.
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osmium tetroxide qn 2 phal sugar a new recyclable catalyst system for Asymmetric Dihydroxylation of olefins
Bulletin of The Korean Chemical Society, 2005Co-Authors: Eun Kyung Kwueon, Doo Seong Choi, Han Young Choi, Yong Jun Lee, Soon Ho Hwang, Yil Sung Park, Choong Eui SongAbstract:E-mail: s1673@skkue.duReceived August 20, 2005Key Words : As ymmetric dihydroxylaton,i Catalyst recycling, Sugar as an immobilization mediumThe international chemistry community is under increas-ing pressure to change current working practices and to findgreener alternatives because of the increasingly stringentenvironmental regulations. This means that chemical manu-facturers need to develop more environmentally sustainableprocesses that produce less waste and avoid, as much aspossbile, the use ofto xic ando/ hr azardousr eagenst .The Sharpless Os-catalyzed Asymmetric Dihydroxylation(AD) of olefins is undoubtedly one of the most efficientmethods of synthesizing chiral vicinal diols.
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osmium tetroxide anchored to porous resins bearing residual vinyl groups a highly active and recyclable solid for Asymmetric Dihydroxylation of olefins
Organic Letters, 2002Co-Authors: Jung Woons Yang, Sanggi Lee, Eun Joo Roh, Hogyu Han, Choong Eui SongAbstract:[reaction: see text] OsO(4) was simply immobilized onto resins such as Amberlite XAD-4 or XAD-7 bearing residual vinyl groups. The resulting osmylated resins are air-stable, nonvolatile, and much easier to handle than their homogeneous counterpart (OsO(4)). Moreover, the resin-bound OsO(4) exhibited excellent catalytic activity in the Asymmetric Dihydroxylation of olefins and was easily recovered and reused in five consecutive reactions without any significant decrease in product yield. Turnover time, however, was significantly increased for the fourth and fifth reactions.
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osmium tetroxide qn 2phal in an ionic liquid a highly efficient and recyclable catalyst system for Asymmetric Dihydroxylation of olefins
Chemical Communications, 2002Co-Authors: Choong Eui Song, Eun Joo Roh, Sanggi Lee, Daun Jung, Dae Yoon ChiAbstract:In Os-catalysed Asymmetric Dihydroxylation using NMO as a co-oxidant, the combination of an ionic liquid and the new bis-cinchona alkaloid 2 generated in situ from (QN)2PHAL during reaction provided a simple and practical approach to the recycling of both catalytic components (osmium tetroxide and chiral ligand).
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efficient and practical polymeric catalysts for heterogeneous Asymmetric Dihydroxylation of olefins
ChemInform, 1996Co-Authors: Choong Eui Song, Jung Woon Yang, Sanggi LeeAbstract:Abstract High enantioselectivity (>99% ee) and reactivity in heterogeneous catalytic Asymmetric Dihydroxylation (AD) of olefins have been achieved using new polymeric cinchona alkaloids containing 1,4-bis(9- O -quininyl)phthalazine ((QN) 2 -PHAL), which can be synthesized more economically than their homogeneous analogue, 1,4-bis(9- O -dihydroquininyl)phthalazine ((DHQ) 2 -PHAL).
