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Hiroyuki Yasuda - One of the best experts on this subject based on the ideXlab platform.
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Magnetically Recoverable Osmium Catalysts with Osmium–Diolate Esters for Dihydroxylation of Olefins
Synlett, 2013Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts with stable osmium–diolate esters and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol with a low level of osmium leaching. After completion of the Dihydroxylation, the osmium catalyst was readily recovered by use of an external magnet and was recycled up to five times.
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magnetically recoverable osmium catalysts with osmium diolate esters for Dihydroxylation of olefins
Synlett, 2013Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts with stable osmium–diolate esters and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol with a low level of osmium leaching. After completion of the Dihydroxylation, the osmium catalyst was readily recovered by use of an external magnet and was recycled up to five times.
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Magnetically recoverable osmium catalysts for Dihydroxylation of olefins
Tetrahedron Letters, 2011Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Manabu Yamazaki, Taku Ainoya, Teruhisa Tsuchimoto, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts by use of magnetite, quaternary ammonium salts, and potassium osmate(VI), and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol in a good chemical yield. The osmium catalyst was readily recovered by use of an external magnet, and was reused repeatedly.
Ken-ichi Fujita - One of the best experts on this subject based on the ideXlab platform.
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Magnetically Recoverable Osmium Catalysts with Osmium–Diolate Esters for Dihydroxylation of Olefins
Synlett, 2013Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts with stable osmium–diolate esters and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol with a low level of osmium leaching. After completion of the Dihydroxylation, the osmium catalyst was readily recovered by use of an external magnet and was recycled up to five times.
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magnetically recoverable osmium catalysts with osmium diolate esters for Dihydroxylation of olefins
Synlett, 2013Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts with stable osmium–diolate esters and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol with a low level of osmium leaching. After completion of the Dihydroxylation, the osmium catalyst was readily recovered by use of an external magnet and was recycled up to five times.
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Magnetically recoverable osmium catalysts for Dihydroxylation of olefins
Tetrahedron Letters, 2011Co-Authors: Ken-ichi Fujita, Satoshi Umeki, Manabu Yamazaki, Taku Ainoya, Teruhisa Tsuchimoto, Hiroyuki YasudaAbstract:We prepared magnetically recoverable osmium catalysts by use of magnetite, quaternary ammonium salts, and potassium osmate(VI), and applied them to the Dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the Dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol in a good chemical yield. The osmium catalyst was readily recovered by use of an external magnet, and was reused repeatedly.
Reinhard Brückner - One of the best experts on this subject based on the ideXlab platform.
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nonracemic γ lactones from the sharpless asymmetric Dihydroxylation of β γ unsaturated carboxylic esters
European Journal of Organic Chemistry, 2016Co-Authors: Markus Neumeyer, Reinhard BrücknerAbstract:Since Sharpless' discovery of the asymmetric Dihydroxylation of C=C double bonds in the late 1980s this reaction has become a powerful tool of synthetic organic chemistry. As a consequence, this transformation has been reviewed repeatedly and extensively. The present microreview focuses on Sharpless' asymmetric Dihydroxylations (from here on “SADs”) of β,γ-unsaturated carboxylic esters. These SADs differ from most others in that they provide not nonracemic 1,2-diols but follow-up products thereof. Bearing ester groups at appropriate distances, the SAD-based 1,2-diols obtained from β,γ-unsaturated carboxylic esters lactonize readily under SAD conditions. Accordingly, SADs of β,γ-unsaturated carboxylic esters furnish nonracemic β-hydroxy-γ-lactones in a single operation. We show that this SAD route represents a – or even the most – potent easy-to-handle route to nonracemic butanolides and butenolides “of almost all kinds”. The span covered is from pioneering racemic work to applications in natural product synthesis. Some non-butanolide and non-butenolide target syntheses are included, especially those of tetrahydrofurans.
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Nonracemic γ‐Lactones from the Sharpless Asymmetric Dihydroxylation of β,γ‐Unsaturated Carboxylic Esters
European Journal of Organic Chemistry, 2016Co-Authors: Markus Neumeyer, Reinhard BrücknerAbstract:Since Sharpless' discovery of the asymmetric Dihydroxylation of C=C double bonds in the late 1980s this reaction has become a powerful tool of synthetic organic chemistry. As a consequence, this transformation has been reviewed repeatedly and extensively. The present microreview focuses on Sharpless' asymmetric Dihydroxylations (from here on “SADs”) of β,γ-unsaturated carboxylic esters. These SADs differ from most others in that they provide not nonracemic 1,2-diols but follow-up products thereof. Bearing ester groups at appropriate distances, the SAD-based 1,2-diols obtained from β,γ-unsaturated carboxylic esters lactonize readily under SAD conditions. Accordingly, SADs of β,γ-unsaturated carboxylic esters furnish nonracemic β-hydroxy-γ-lactones in a single operation. We show that this SAD route represents a – or even the most – potent easy-to-handle route to nonracemic butanolides and butenolides “of almost all kinds”. The span covered is from pioneering racemic work to applications in natural product synthesis. Some non-butanolide and non-butenolide target syntheses are included, especially those of tetrahydrofurans.
Mikko H. Junttila - One of the best experts on this subject based on the ideXlab platform.
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Methanesulfonamide: a cosolvent and a general acid catalyst in sharpless asymmetric Dihydroxylations.
The Journal of organic chemistry, 2009Co-Authors: Mikko H. Junttila, Osmo O. E. HormiAbstract:To obtain information about the effect that methanesulfonamide has in the hydrolysis step in Sharpless asymmetric Dihydroxylation, a series of aliphatic and conjugated aromatic olefins were dihydroxylated with and without methanesulfonamide. The hypothesis in this study was that methanesulfonamide is a cosolvent that aids in the transfer of the hydroxide ions from the water phase to the organic phase. A plot of t90% versus the computational partition coefficient clog P of the intermediate osmate ester of nonterminal aliphatic olefins revealed that the polarity of the intermediate osmate ester has a significant effect on the reaction time and methanesulfonamide effect. The more polar the intermediate osmate ester, the faster is the reaction without methanesulfonamide and the smaller the accelerating methanesulfonamide effect. Methanesulfonamide had no accelerating effect in the asymmetric Dihydroxylation of short chain terminal aliphatic olefins as a result of easier accessibility of terminal osmate ester groups to the water phase. A cosolvent hypothesis was found not to be valid in asymmetric Dihydroxylations of conjugated aromatic olefins. In the reaction conditions used in Sharpless asymmetric Dihydroxylation, weakly acidic methanesulfonamide was found to be a general acid catalyst that protonates the intermediate osmate esters of conjugated aromatic olefins in the hydrolysis step.
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On the hydrolysis step in osmium catalyzed asymmetric Dihydroxylations.
The Journal of organic chemistry, 2007Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:In order to obtain information about the most important features that affect the efficiency of osmium catalyzed asymmetric Dihydroxylation, a series of substituted styrenes have been studied by using a Hammett type approach as well as solvent kinetic isotope effects. A concave shaped Hammett plot with a minimum at X = H revealed a change in the mechanism going from electron-donating to electron-withdrawing substituents for both NaClO2 and K3[Fe(CN)6] asymmetric Dihydroxylations. The Hammett plot together with solvent isotope effect results indicates that osmium (mono)glycolates of styrenes with electron-withdrawing substituents are hydrolyzed by a stepwise attack of the nucleophile to the electrophilic osmium-center and subsequent protonation of the alkaline intermediate. Osmium (mono)glycolates in Dihydroxylation, using NaClO2 as the stoichiometric oxidant of styrenes with electron-donating substituents, are hydrolyzed by specific acid catalysis. The rate-limiting step is an A1 type process. Differences ...
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Sodium Chlorite as an Efficient Oxidant and Hydroxy Ion Pump in Osmium‐Catalyzed Asymmetric Dihydroxylation.
ChemInform, 2004Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric Dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric Dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] Dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes.
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sodium chlorite as an efficient oxidant and hydroxy ion pump in osmium catalyzed asymmetric Dihydroxylation
Journal of Organic Chemistry, 2004Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric Dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric Dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] Dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes.
Osmo E. O. Hormi - One of the best experts on this subject based on the ideXlab platform.
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On the hydrolysis step in osmium catalyzed asymmetric Dihydroxylations.
The Journal of organic chemistry, 2007Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:In order to obtain information about the most important features that affect the efficiency of osmium catalyzed asymmetric Dihydroxylation, a series of substituted styrenes have been studied by using a Hammett type approach as well as solvent kinetic isotope effects. A concave shaped Hammett plot with a minimum at X = H revealed a change in the mechanism going from electron-donating to electron-withdrawing substituents for both NaClO2 and K3[Fe(CN)6] asymmetric Dihydroxylations. The Hammett plot together with solvent isotope effect results indicates that osmium (mono)glycolates of styrenes with electron-withdrawing substituents are hydrolyzed by a stepwise attack of the nucleophile to the electrophilic osmium-center and subsequent protonation of the alkaline intermediate. Osmium (mono)glycolates in Dihydroxylation, using NaClO2 as the stoichiometric oxidant of styrenes with electron-donating substituents, are hydrolyzed by specific acid catalysis. The rate-limiting step is an A1 type process. Differences ...
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Sodium Chlorite as an Efficient Oxidant and Hydroxy Ion Pump in Osmium‐Catalyzed Asymmetric Dihydroxylation.
ChemInform, 2004Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric Dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric Dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] Dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes.
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sodium chlorite as an efficient oxidant and hydroxy ion pump in osmium catalyzed asymmetric Dihydroxylation
Journal of Organic Chemistry, 2004Co-Authors: Mikko H. Junttila, Osmo E. O. HormiAbstract:Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric Dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric Dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] Dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes.