Rhodium asymmetric hydrogenation

The problems which remain in understanding and interpreting rhodium asymmetric hydrogenation arise from a persistent lack of information on the presumed rhodium dihydride without which the pathway between the enamide complex and the turnover limiting TS for H2 addition (i.e. the step in which the enantioselectivity of the reaction is set) remains opaque, and hence the overall understanding is elusive. [52]... 

In order to appreciate the mechanism of rhodium asymmetric hydrogenation, it may be useful first to examine the simpler achiral case of alkene hydrogenation by Wilkinson s catalyst. In early studies [13] assumptions were made about the dihydrogen activation step which proved to be incorrect because of the direct... 

The classical application of rhodium asymmetric hydrogenation has been the synthesis of amino-acids from dehydroamino acids, as was seen earlier. The reaction has been applied in more complex cases, for example, the hydrogenation... 

Fig. 22. Some new ligands for rhodium asymmetric hydrogenation (1992 on) of dehydroamino...

The formation of ci5-dihydride in iridium complexes related to rhodium asymmetric hydrogenation catalysts has been observed at low temperature see equation (12). They rearrange to a different dihydride at —45 C and react at —25 °C... 

Asymmetric hydrogenation has been achieved with dissolved Wilkinson type catalysts (A. J. Birch, 1976 D. Valentine, Jr., 1978 H.B. Kagan, 1978). The (R)- and (S)-[l,l -binaph-thalene]-2,2 -diylblsCdiphenylphosphine] (= binap ) complexes of ruthenium (A. Miyashita, 1980) and rhodium (A. Miyashita, 1984 R. Noyori, 1987) have been prepared as pure atrop-isomers and used for the stereoselective Noyori hydrogenation of a-(acylamino) acrylic acids and, more significantly, -keto carboxylic esters. In the latter reaction enantiomeric excesses of more than 99% are often achieved (see also M. Nakatsuka, 1990, p. 5586). 

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... 

Efficient enantioselective asymmetric hydrogenation of prochiral ketones and olefins has been accompHshed under mild reaction conditions at low (0.01— 0.001 mol %) catalyst concentrations using rhodium catalysts containing chiral ligands (140,141). Practical synthesis of several optically active natural... 

The influence of the concentration of hydrogen in [BMIM][PFg] and [BMIM][BF4] on the asymmetric hydrogenation of a-acetamidocinnamic acid catalyzed by rhodium complexes bearing a chiral ligand has been investigated. FFydrogen was found to be four times more soluble in the [BFJ -based salt than in the [PFg] -based one. 

Ethane, (K)-l-cyclohexyl-L2-bis(diphenylphosphino)-rhodium complexes asymmetric hydrogenation, 6,253 Ethane, tetracyano-metal complexes, 2,263 Ethane, tetrakis(aminomethyl)-metal complexes, 2, 56 Ethane, tris[l, 1, l-(trisaminomethyl)]-complexes structure, 1,26... 

Phosphine, (2-bromophenyl)dichloro-, 2,991 Phosphine, (w-chloroalkyl)dichloro-, 2, 991 Phosphine, chlorodimethyl-, 2, 991 Phosphine, chloro(dimethylamino)-, 2, 991 Phosphine, chlorodiphenyl-, 2, 990 Phosphine, cyclohexyl(o-anisyl)methyl-rhodium complexes asymmetric hydrogenation, 6, 251 Phosphine, [(dialkylphosphino)alkyl]diphenyl-, 2, 994 Phosphine, dichloromethyl-, 2, 991 Phosphine, dichlorophenyl-, 2, 990 Phosphine, diethylphenyl-, 2, 992 Phosphine, dimethyl-, 2,992 Phosphine, dimethylphenyl-, 2,992 Phosphine, diphenyl-, 2, 992 Phosphine, ethyldiphenyl-, 2, 992 Phosphine, ethylenebis(diethyl-, 2, 993 Phosphine, ethylenebis(diphenyl-, 2,993 Phosphine, ethylenebis(phenyl-, 2,992 Phosphine, ethylidynetris[methylene(diphenyl-, 2,994 Phosphine, [(ethylphenylphosphino)hexyl]diphenyl-, 2, 994... 

Phosphine, methyl-n-propylphenyl-rhodium complexes asymmetric hydrogenation, 6,250 Phosphine, neomenthyldiphenyl-rhodium complexes asymmetric hydrogenation, 6,250 Phosphine, phenyl-, 2,992 Phosphine, o-phenylenebis(dimethyl-, 2,993 Phosphine, p-phenylenebis(diphenyl-, 2,993 Phosphine, seleno-metal complexes, 2,664 bidentatc, 2, 664 Phosphine, triaryl-photographic stabilizer, 6,103 Phosphine, tributyl-, 2, 992 oxide... 

Propane, (J )-1,2-bis(diphenylphosphino)-rhodium complexes asymmetric hydrogenation, 6, 251... 

Styrene, a-ethyl-asymmetric hydroformylation catalysts, platinum complexes, 6, 266 asymmetric hydrogenation catalysts, rhodium complexes, 6, 250 Styrene, a-methyl-asymmetric carbonylation catalysis by palladium complexes, 6, 293 carbonylation... 

In 1968,Horner et al. [22] and Knowles and Sabacky [23] independently demonstrated that low but definite enantiomeric excesses (up to 15% ee) were produced in the rhodium-catalyzed asymmetric hydrogenation of simple alkenes using methylpropylphenylphosphine 7 as chiral ligand (Scheme 1). 

The rhodium complex of the (R,R)-counter-enantiomer of (S,S)-BisP achieved a high level of ee (97%) in the asymmetric hydrogenation of 3-methoxy-substituted substrate (S)-122 (Scheme 25), which constitutes a precursor to the acetylcholinesterase inhibitor SDZ-ENA-713 (123). 

In general, of the mixed phosphorus-thioether ligands that have been used in the asymmetric hydrogenation of prochiral olefins, the thioether-phosphinite ligands have provided some of the best results. As an example, a new class of thioether-phosphinite ligands developed by Evans et al. has recently proved to be very efficient for the rhodium-catalysed asymmetric hydrogenation of a... 

In 2006, Berens et al. reported the synthesis of novel benzothiophene-based DuPHOS analogues, which gave excellent levels of enantioselectivity when applied as the ligands to the asymmetric rhodium-catalysed hydrogenation of various olefins, such as dehydroamino acid derivatives, enamides and itaco-nates (Scheme 8.10). ... 

Several S/N ligands have also been investigated for the asymmetric hydrogenation of prochiral olefins. Thus, asymmetric enamide hydrogenations have been performed in the presence of S/N ligands and rhodium or ruthenium catalysts by Lemaire et al., giving enantioselectivities of up to 70% ee. Two... 

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