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Asymmetric metallation

Chiral cyclic phosphines have useful properties as ligands in transition metal asymmetric catalytic systems. The most impressive example is the five-membered ring phosphorus (phospholane)-based chiral ligand DuPFIOS <2000ACR363>. [Pg.494]

All of the above examples involve an extra coordinating group such as ena-mide, acid, or ester in the substrate. This is necessary for optimum coordination to the metal. Asymmetric hydrogenation of olefins without functional groups is an emerging area [80]. [Pg.108]

Pini, D., Petri, A., Mastantuono, A., Salvador , P. Heterogeneous enantioselective hydrogenation and dihydroxylation of carbon carbon double bond mediated by transition metal asymmetric catalysts. Chiral Reactions In Heterogeneous Catalysis, [Proceedings of the European Symposium on Chiral Reactions In Heterogeneous Catalysis], 1st, Brussels, Oct. 25-26, 1993 1995, 155-176. [Pg.673]

CO sometimes bridges metals asymmetrically in these cases CO is considered semibridging (shown below). [Pg.79]

The desire to produce enantiomerically pure pharmaceuticals and other fine chemicals has advanced the field of asymmetric catalytic technologies. Since the independent discoveries of Knowles and Homer [1,2] the number of innovative asymmetric catalysis for hydrogenation and other reactions has mushroomed. Initially, nature was the sole provider of enantiomeric and diastereoisomeric compounds these form what is known as the chiral pool. This pool is comprised of relatively inexpensive, readily available, optically active natural products, such as carbohydrates, hydroxy acids, and amino acids, that can be used as starting materials for asymmetric synthesis [3,4]. Before 1968, early attempts to mimic nature s biocatalysis through noble metal asymmetric catalysis primarily focused on a heterogeneous catalyst that used chiral supports [5] such as quartz, natural fibers, and polypeptides. An alternative strategy was hydrogenation of substrates modified by a chiral auxiliary [6]. [Pg.143]

Reduction via hydrosilylation with trichlorosilane does not requires a metal. Asymmetric reduction is achieved in the presence of the picolinic amide of (lR,25)-ephedrine, or an... [Pg.153]

For the last few year the catalytic asymmetric synthesis of tertiary phosphines has attracted the attention of many chemists. Interesting results were published in many articles and reviews [109-115]. Catalyzed by transition metals, asymmetric phosphination of secondary, racemic phosphines with aryl halides or triflates to prepare a tertiary P-stereogenic phosphines with control of the stereochemistry at the phosphorus atom is shown in Scheme 62. [Pg.201]

CH3—M (M = metal) Asymmetric stretch Symmetric stretch Dependent to a small extent on M ... [Pg.209]

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. [Pg.61]

Catalytic asymmetric hydrogenation was one of the first enantioselective synthetic methods used industrially (82). 2,2 -Bis(diarylphosphino)-l,l -binaphthyl (BINAP) is a chiral ligand which possesses a Cg plane of symmetry (Fig. 9). Steric interactions prevent interconversion of the (R)- and (3)-BINAP. Coordination of BINAP with a transition metal such as mthenium or rhodium produces a chiral hydrogenation catalyst capable of inducing a high degree of enantiofacial selectivity (83). Naproxen (41) is produced in 97% ee by... [Pg.248]

This chemical bond between the metal and the hydroxyl group of ahyl alcohol has an important effect on stereoselectivity. Asymmetric epoxidation is weU-known. The most stereoselective catalyst is Ti(OR) which is one of the early transition metal compounds and has no 0x0 group (28). Epoxidation of isopropylvinylcarbinol [4798-45-2] (1-isopropylaHyl alcohol) using a combined chiral catalyst of Ti(OR)4 and L-(+)-diethyl tartrate and (CH2)3COOH as the oxidant, stops at 50% conversion, and the erythro threo ratio of the product is 97 3. The reason for the reaction stopping at 50% conversion is that only one enantiomer can react and the unreacted enantiomer is recovered in optically pure form (28). [Pg.74]

Direct Blue 218 had reported sales of 623 t valued at 4.4 million ia 1987. It is produced from Direct Blue 15 (76) by metallizing and elimination of methyl groups from the methoxide to form the copper complex. Direct Blue 15 (76) is prepared by coupling o-dianisidine [119-90-4] to two moles of H-acid (4-amiQO-5-hydroxy-2,7-naphthalenedisulfonic acid) under alkaline pH conditions. Other important direct blues iaclude Direct Blue 80 (74), (9-dianisidine coupled to two moles of R-acid (3-hydroxy-2,7-naphthalenedisulfonic acid [148-75-4]) followed by metallizing to form a bis copper complex, and Direct Blue 22 (77), an asymmetrical disazo dye, prepared by coupling o-dianisidine to Chicago acid [82-47-3] and 2-naphthol. Direct Blue 75 (78) is an example of a trisazo dye represented as metanilic acid — 1,6-Q.eve s acid — 1,6-Q.eve s acid — (alb) Ai-phenyl J-acid. [Pg.443]

Transition metal-catalyzed epoxidations, by peracids or peroxides, are complex and diverse in their reaction mechanisms (Section 5.05.4.2.2) (77MI50300). However, most advantageous conversions are possible using metal complexes. The use of t-butyl hydroperoxide with titanium tetraisopropoxide in the presence of tartrates gave asymmetric epoxides of 90-95% optical purity (80JA5974). [Pg.36]

Table 28.1 Momentary peak (maximum r.m.s.) current ratings, asymmetrical, for switchgear and metal-enclosed bus systems, based on ANSI-C-37/20C... Table 28.1 Momentary peak (maximum r.m.s.) current ratings, asymmetrical, for switchgear and metal-enclosed bus systems, based on ANSI-C-37/20C...
The reduction of an asymmetric cyclohexanone (e.g. a steroidal ketone) can lead to two epimeric alcohols. Usually one of these products predominates. The experimental results for the reduction of steroidal ketones with metal hydrides have been well summarized by Barton and are discussed in some detail in a later section (page 76) unhindered ketones are reduced by hydrides to give mainly equatorial alcohols hindered ketones (more accurately ketones for which axial approach of the reagent is hindered " ) are reduced to give mainly axial alcohols. [Pg.67]

The XRD peaks characteristic of Co and Ni disappeared after the treatment, as did the broad ESR line, successfully leaving only the narrow asymmetric line with 26 G linewidth as shown in Fig. 8 [40]. The g-value of the narrow line is =2.002 0.001. The narrow ESR line shows Dysonian at all temperatures in the range of 4-300 K. Furthermore, the ESR intensity is quite independent of T and thus the density of conduction electrons is invariant as a function of temperature as shown in Fig. 9. These show that the material is highly metallic, even at low 7. [Pg.85]

Chiral oxazolines developed by Albert I. Meyers and coworkers have been employed as activating groups and/or chiral auxiliaries in nucleophilic addition and substitution reactions that lead to the asymmetric construction of carbon-carbon bonds. For example, metalation of chiral oxazoline 1 followed by alkylation and hydrolysis affords enantioenriched carboxylic acid 2. Enantioenriched dihydronaphthalenes are produced via addition of alkyllithium reagents to 1-naphthyloxazoline 3 followed by alkylation of the resulting anion with an alkyl halide to give 4, which is subjected to reductive cleavage of the oxazoline moiety to yield aldehyde 5. Chiral oxazolines have also found numerous applications as ligands in asymmetric catalysis these applications have been recently reviewed, and are not discussed in this chapter. ... [Pg.237]

The mechanism of the asymmetric alkylation of chiral oxazolines is believed to occur through initial metalation of the oxazoline to afford a rapidly interconverting mixture of 12 and 13 with the methoxy group forming a chelate with the lithium cation." Alkylation of the lithiooxazoline occurs on the less hindered face of the oxazoline 13 (opposite the bulky phenyl substituent) to provide 14 the alkylation may proceed via complexation of the halide to the lithium cation. The fact that decreased enantioselectivity is observed with chiral oxazoline derivatives bearing substituents smaller than the phenyl group of 3 is consistent with this hypothesis. Intermediate 13 is believed to react faster than 12 because the approach of the electrophile is impeded by the alkyl group in 12. [Pg.238]


See other pages where Asymmetric metallation is mentioned: [Pg.186]    [Pg.994]    [Pg.246]    [Pg.361]    [Pg.209]    [Pg.168]    [Pg.186]    [Pg.994]    [Pg.246]    [Pg.361]    [Pg.209]    [Pg.168]    [Pg.36]    [Pg.22]    [Pg.25]    [Pg.629]    [Pg.397]    [Pg.397]    [Pg.23]    [Pg.25]    [Pg.138]    [Pg.184]    [Pg.189]    [Pg.350]    [Pg.344]    [Pg.393]    [Pg.171]    [Pg.388]    [Pg.588]    [Pg.445]    [Pg.451]    [Pg.512]    [Pg.216]    [Pg.56]    [Pg.779]    [Pg.10]    [Pg.240]   


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Asymmetric Mannich reactions, metal-free

Asymmetric alkali-metal catalyst

Asymmetric allylation metal reactions

Asymmetric catalysis with transition metal

Asymmetric epoxidation chiral metal complex catalysis

Asymmetric epoxidation transition metal catalysts

Asymmetric hydrogenation on metal-quartz catalysts

Asymmetric hydrogenations over chiral metal

Asymmetric hydrogenations over chiral metal complexes immobilized in SILCA

Asymmetric induction using chiral transition metal catalysts

Asymmetric metal complex catalysts

Asymmetric metal-catalyzed sulfoxidations

Asymmetric metal-catalyzed sulfoxidations chiral catalysts

Asymmetric metallation chromium tricarbonyl

Asymmetric metallation complexes

Asymmetric oxidation, metal-catalyzed

Asymmetric oxidation, metal-catalyzed sulfoxidations

Asymmetric phase-transfer catalysis metal enolates

Asymmetric reductive amination metal catalysts

Asymmetric synthesis metal chelates and

Asymmetric transfer hydrogenation catalyzed, metal-ligand

Asymmetrical metal atoms

Chiral catalysts, asymmetric metal-catalyzed

Chiral metal complexes asymmetric synthesis

Chirality asymmetric metal catalysis

Cinchona metal-catalyzed asymmetric oxidations

Combinatorial asymmetric transition metal

Combinatorial asymmetric transition metal catalysis

Dealloyed Precious Metals on Teflon or Asymmetric Membranes

Dynamic kinetic asymmetric metal-catalyzed racemization

Ethers, Taddol, Nobin and Metal(salen) Complexes as Chiral Phase-Transfer Catalysts for Asymmetric Synthesis

Group 4 metal-promoted oxidations asymmetric oxidation of sulfides

Group 8 metal-promoted oxidations alkene cleavage and asymmetric dihydroxylation

Hydrosilylation, metal-catalysed asymmetric

Imines transition metal catalyzed asymmetric

Lanthanide-Alkali Metal Heterobimetallic Asymmetric Catalysts

Merging Asymmetric Metal and Organocatalysis in Friedel-Crafts Alkylations

Metal asymmetric Heck reaction

Metal enolates, asymmetric protonation

Metal groups asymmetric allylation

Metal heterogeneous asymmetric hydrogenation

Metal-catalyzed asymmetric reductions

Metal-catalyzed asymmetric synthesis

Metal-catalyzed reactions asymmetric

Metallated chiral asymmetric alkylation

Metallation, asymmetric diastereoselective

Oxidation reactions, transition-metal asymmetric epoxidation

Polydentate Metal Complexes and Asymmetric Syntheses

Sulfoximines as Ligands in Asymmetric Metal Catalysis

Transition metal catalysis asymmetric hydrogenation

Transition metal catalysis asymmetric reduction

Transition metal catalysts asymmetric reductive amination

Transition metal catalysts asymmetric sulfoxidation

Transition metals elements asymmetric hydrogenation

Transition-metal-catalyzed asymmetric

Transition-metal-catalyzed asymmetric reactions

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