New ligands double the scope of the catalytic asymmetric dihydroxylation of olefins
TL;DR: Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process as discussed by the authors.
Abstract: Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process, and the amounts of chiral ligand and osmium catalyst required diminish dramatically
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TL;DR: A. Lanthanum, Yttrium, and Scandium 2126 B. Hafnium, Zirconium and Titanium 2126 C. Tantalum, Niobium, and Vanadium 2127 D. Tungsten, Molybdenum, and Chromium 2127 E. Osmium, Ruthenium, iron, and iron 2128 1. Osmylation 2128 2. Reactions with Zerovalent Compounds 2131 3. Redox Reactions 2134 5.
Abstract: A. Lanthanum, Yttrium, and Scandium 2126 B. Hafnium, Zirconium, and Titanium 2126 C. Tantalum, Niobium, and Vanadium 2127 D. Tungsten, Molybdenum, and Chromium 2127 E. Rhenium, Technetium, and Manganese 2128 F. Osmium, Ruthenium, and Iron 2128 1. Osmylation 2128 2. Reactions with Zerovalent Compounds 2131 3. Other Addition Reactions 2133 4. Redox Reactions 2134 5. Cocrystallizations 2134 G. Iridium, Rhodium, and Cobalt 2135 1. Adduct Formation with Vaska-Type Complexes, Ir(CO)Cl(PR3)2 2135
440 citations
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TL;DR: On the basis of the newly proposed hypothesis on the mechanism of asymmetric induction, highly efficient (salen)manganese(III) complex was constructed as a catalyst for asymmetric epoxidation.
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TL;DR: In this article, the authors evaluated the performance of two different types of catalysts for asymmetric dihydroxylation of trans-stilbene, namely, Resin-OsO 4 and SiO 2 -OsO4, and showed consistent activity and enantioselectivity in asymmetric diolation using K 3 Fe(CN) 6 and molecular oxygen as cooxidants.
Abstract: Exchanger-OsO 4 catalysts are prepared by an ion-exchange technique using layered double hydroxides and quaternary ammonium salts covalently bound to resin and silica as ion-exchangers. The ion-exchangers with different characteristics and opposite ion selectivities are specially chosen to produce the best heterogeneous catalyst that can operate using the various cooxidants in the asymmetric dihydroxylation reaction. LDH-OsO 4 catalysts composed of different compositions are evaluated for the asymmetric dihydroxylation of trans-stilbene. Resin-OsO 4 and SiO 2 -OsO 4 designed to overcome the problems associated with LDH-OsO 4 indeed show consistent activity and enantioselectivity in asymmetric dihydroxylation of olefins using K 3 Fe(CN) 6 and molecular oxygen as cooxidants. Compared to the Kobayashi heterogeneous systems, resin-OsO 4 is a very efficient catalyst for the dihydroxylation of a wide variety of aromatic, aliphatic, acyclic, cyclic, mono-, di-, and trisubstituted olefins to afford chiral vicinal diols with high yields and enantioselectivities irrespective of the cooxidant used. Resin-OsO 4 is recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity. The high binding ability of the heterogeneous osmium catalyst enables the use of an equimolar ratio of ligand to osmium to give excellent enantioselectives in asymmetric dihydroxylation in contrast to the homogeneous osmium system in which excess molar quantities of the expensive chiral ligand to osmium are invariably used. The complexation of the chiral ligand (DHQD) 2 PHAL, having very large dimension, a prerequisite to obtain higher ee, is possible only with the OsO 4 2- located on the surface of the supports.
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TL;DR: The chiral fullerene C76 was kinetically resolved by asymmetric osmylation providing an example of an optically active allotrope of a pure element and regioselectivity was supported chromatographically and interpreted in terms of the kinetic resolution.
Abstract: The chiral fullerene C76 was kinetically resolved by asymmetric osmylation providing an example of an optically active allotrope of a pure element. C76 recovered from the treatment of racemic C76 with OsO4 and a chiral alkaloid ligand, showed a specific rotation [α]D of -4000° (> 97 percent enantiomeric excess) and a circular dichroism spectrum corresponding to the ultraviolet spectrum. Regenerated C76 formed by reducing the asymmetrically osmylated C76 with SnCl2 was enriched in the opposite enantiomer. Analysis of the local curvature of the C76 molecule indicated that OsO4 should selectively add to 2 of the 30 types of bonds in C76. This regioselectivity was supported chromatographically and interpreted in terms of the kinetic resolution.
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TL;DR: In this article, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms.
Abstract: OF THE DISCLOSURE Methods and compositions are provided for asymecrically donating an oxygen atom to a pair of electrons to produce an asymmetric product. Specifically, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms. The metal catalyst is employed in conjunction with a hydroperoxide and an alkanol having a functionality with a pair of electrons capable of accepting an oxygen atom. The resulting product is enriched in one enantiomer due to the enantioselective introduction of an asymmetric center or an enhanced rate of reaction of one of the enantiomers of a chiral alkanol. Greatly enhanced yields of enantiomers are achieved as compared to prior enantioselective introduction of oxygen. This invention was made at least in part in the course of a grant from the U.S. National Institutes of Health (GM24551).
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TL;DR: Dihydroxylation asymetrique de composes ethyleniques du type styrene, vinylcyclohexane, hexene-3 en les glycols correspondants as mentioned in this paper.
Abstract: Dihydroxylation asymetrique de composes ethyleniques du type styrene, vinylcyclohexane, hexene-3 en les glycols correspondants
619 citations
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TL;DR: In this paper, the methode presentee se fait au depart de phenyl-3 dihydroxy-2,3 propionate de methyle via epoxydation, et d'azoture de sodium.
Abstract: La methode presentee se fait au depart de phenyl-3 dihydroxy-2,3 propionate de methyle, via une epoxydation, et d'azoture de sodium; des N-t-butoxycarbonyl- et N-benzoyl phenylisoleucinates de methyle sont obtenus
195 citations