Hydrogenation Of Α-acetamidocinnamic Acid Research Articles

Chiral rhodium complexes covalently anchored on carbon nanotubes for enantioselective hydrogenation

Chiral rhodium hybrid nanocatalysts have been prepared by covalent anchorage of pyrrolidine-based diphosphine ligands onto functionalized CNTs. This work constitutes the first attempt at covalent anchoring of homogeneous chiral catalysts on CNTs. The catalysts, prepared with two different chiral phosphines, were characterized by ICP, XPS, N2 adsorption and TEM, and have been tested in the asymmetric hydrogenation of two different substrates: methyl 2-acetamidoacrylate and α-acetamidocinnamic acid. The hybrid nanocatalysts have shown to be active and enantioselective in the hydrogenation of α-acetamidocinnamic acid. A good recyclability of the catalysts with low leaching and without loss of activity and enantioselectivity was observed.

Enantioselektive Katalyse, 63 [1] Optisch Aktive Phosphine Aus Dicarbonsäuren Und Ihr Einsatz in Der Enantioselektiven Hydrierung

Two optically active bident phosphine ligands were synthesized from derivatives of succinic acid as starting materials. The optical resolution of the acids was carried out with cinchonidine and (S)-α-phenylethylamine. In the Rh-catalyzed enantioselective hydrogenation of α-acetamidocinnamic acid, the bisphosphine with a phenyl substituent in the 2-position of the four-carbon chain gave an enantiomeric excess of 17%. The enantiomeric excess was twice as high with the corresponding thienyl substituted bisphosphine.

Rh-catalyzed asymmetric hydrogenation by using a new family of C2-symmetric bisphosphinites and a bisaminophosphine as ligands

The application of a new family of four-chiral-centered C 2-symmetric bisphosphinites ( 1 , 2 and 3 ) and the bisaminophosphine 4 in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids has been examined. Up to 98% ee was obtained in the hydrogenation of α-acetamidocinnamic acid, which is comparable with the enantioselection obtained from the best chiral bisphosphinites and bisaminophosphines.

Chiral rhodium carboxylates as asymmetric hydrogenation catalysts

The comparative catalytic activities of a few chiral rhodium carboxylato complexes in combination with chiral and achiral phosphines are described. In the hydrogenation of α-acetamidocinnamic acid and its methyl ester, differences are observed in turnover numbers and enantioselectivities. Diastereomeric interactions between chiral carboxylato and chiral phosphine moieties resulting in different rates are clearly seen. Arrhenius plots of (+) and (-) DIOP [DIOP = 2,3 isopropylidene 2,3 dihydroxy-1,4bis (diphenylphosphino) butane] with rhodium (-) mandalato complex give markedly different activation energies.

Diphenylphosphin-substituiertes, chirales Polyepichlorhydrin, ein Träger für die heterogene, asymmetrische Katalyse / Diphenylphosphine-Substituted, Chiral Polyepichlorohydrin, a Support for the Heterogeneous, Asymmetric Catalysis

Chiral polyepichlorohydrin was obtained as a crystalline, optically active powder by coordinative polymerization of S(+)-epichlorohydrin. Subsequent reaction with lithium diphenylphosphide in THF resulted in substitution of about 90% of the chlorine atoms by the P(C6H5)2 group to give an insoluble polymer, which was characterized by elemental analysis, 31P CP MAS NMR, and IR spectroscopy. On addition of solutions of bis(1.5-cyclooctadiene)-rhodium tetrafluoroborate to the polymer “heterogenization” of the complex occurred. The reason for the as yet short operational life time during the hydrogenation of α-acetamido cinnamic acid is the leaching of the metal complex moiety. The rhodium atom is coordinated to only one phosphorus atom of the polymer in the side group and rather weakly to one oxygen atom of the polymer chain.

Homogeneous asymmetric catalysis by means of chiral metal complexes of 2,3-bis(dimenthylphosphino)maleic anhydride and of 2,3-bis(dimenthylphosphino)maleimide derivatives

2,3-Bis(dimenthylphosphino)maleic anhydride and also 2,3-bis(dimenthylphosphino)maleimide derivatives have been prepared from 2,3-dichloromaleic anhydride, 2,3-dichloro- N-phenylmaleimide and 2,3-dichloro- N-methylmaleimide, respectively, and dimenthyl(trimethylsilyl)phosphine. These compounds have been used as ligands for Rh complexes in the asymmetric hydrogenation and hydrosilylation. Ni and Pd complexes of these ligands were tested in the Grignard cross-coupling reaction. The hydrogenation of α-acetamido cinnamic acid gave 70% enantiomeric excess (ee) and hydrogenation of acetophenone up to 47% ee. Hydrosilylation of acetophenone led to 42% ee. Attempts to asymmetric cross-coupling reactions resulted in very low enantiomeric excess.

Catalytic Asymmetric Hydrogenation of α-Acetamido Cinnamic Acids

Abstract The homogeneous catalytic asymmetric hydrogenations of substituted cinnamic acids by (l-Benzyl-3,4-(R,R)-bis(diphenyl-phosphino) pyrrolidine (COD) Rh)BF4 6, easily prepared from L-tartaric acid has been studied. Contrary to other catalysts, this Rhodium (I) complex affords very high chemical and optical yields of N-acetylated amino acids under mild conditions even when using substrate to catalyst ratio as high as 16000. The method has been successfully applied for the preparation of L-Phenylalanine and L-Dopa.

Asymmetric hydrogenation of .ALPHA.-acetamidocinnamic acid with chiral rhodium complexes of DIOP and BPPM on charcoal.

Chiral rhodium (I) complexes of (-)-2, 3-O-isopropylidene-2, 3-dihydroxy-1, 4-bis (diphenylphosphino) butane (DIOP) and (2S, 4S) -N-butoxycarbonyl-4-diphenylphosphino-2-diphenyl-phosphinomethylpyrrolidine (BPPM) were fixed on charcoal which had been pretreated with metal acetates and triethylamine, and the hydrogenation of α-acetamidocinnamic acid was performed in an ethanol-H2O (1 : 1) mixture. L-N-Acetyl- (R) -phenylalanine was obtained in optical yields of 70.5% with RhCl (COD) -DIOP-charcoal catalyst and 86.5% with RhCl (COD) -BPPM-charcoal catalyst. The optical yields were affected by hydrogen pressure, reaction temperature, the concentration of the substrate, and the composition of the solvent. The recovered catalyst retained its activity well and could be re-used repeatedly for enantioface-differentiating hydrogenation, provided that it was kept under a nitrogen atmosphere throughout.

Asymmetric hydrogenation in the presence of bicyclic chiral phosphines

Both enantiomers of trans-2,3-diphenylphosphinomethyl-norbornene-(5), prepared by two independent synthetic routes, were used as ligands in the asymmetric hydrogenation of α-acetamidocinnamic acid in the presence of rhodium(I). Small variations in the ligand structure have a remarkable influence on the activity of the catalytic system.

Versuche zur Rhodium(I)-katalysierten asymmetrischen Hydrierung von α-Acetamidozimtsäure mit monomeren und polymeren Aminophosphinen / Rhodium (I) Catalyzed Asymmetric Hydrogenation of α-Acetamido Cinnamic Acid with Monomeric and Polymeric Aminophosphines

An optically active 1-phosphino-2-aminopropane, prepared from ephedrine, has been used for the Rh(I) catalyzed asymmetric hydrogenation of α-acetamido cinnamic acid. Optical yields up to 77 percent were obtained. Low stereoselectivity has been found using 1,4-bis(diphenylphosphino)-2,5-dibenzylpiperazine and a polystyrene bound bisdiphenyl-phosphine, obtained from phenylalanine. The preparation of optically active piperazines from α-amino acids is reported

ASYMMETRIC HYDROGENATION WITH CHIRAL PHOSPHINE LIGAND HAVING C-PPh2 BONDING DERIVED FROM d-GLUCOSE

Abstract Rh-complex of 6S-cyano-5R-diphenylphosphino-3R,4S-O-isopropylidene-2-oxa-bicyclo[3.2.0]heptane showed the relatively high enantioselectivity (S-configuration) in the hydrogenation of α-acetamidocinnamic acid, whereas Rh-complex of the 6S-aminomethyl compound, the reduction product of the former, gave the reversed enantioselectivity (R-configuration) in the reaction.

Asymmetric hydrogenation using ferrocenylphosphine rhodium(I) cationic complexes

High optical yields are obtained in the hydrogenation of α-acetamidocinnamic acid using [(COD)Rh((+)PPFA)]ClO 4 and related complexes as catalysts. (+)PPFA is (S)-α-[(R)-2-diphenylphosphinoferrocenyl] ethyldimethylamine.

A rhodium-DIOP complex attached to an inorganic support as catalyst for enantioselective syntheses

A rhodium-DIOP complex attached to a macroporous silica gel has been tested as catalyst for the enantioselective hydrosilylation of acetophenone and hydrogenation of α-acetamidocinnamic acid. The catalyst has been found to be comparable in asymmetric efficiency to homogeneous analogues. In both reactions, the activity of the heterogenized catalyst was by ca. one order of magnitude lower relative to the homogeneous system.

Stereospecific Hydrogenations V: Hydrogenation Rates Using Palladium-on-Poly-S-leucine and Palladium-on-Poly-S-valine

The effect of polyamino acid secondary structure (helical or nonhelical) on the rates of hydrogenations of α-methylcinnamic acid and α-acetamidocinnamic acid catalyzed by palladium-on-poly-S-leucine and by palladium-on-poly-S-valine was investigated. For each substrate, the hydrogenations proceeded at a faster rate with palladium-on-poly-S-leucine (helical catalyst) than with palladium-on-poly-S-valine (nonhelical catalyst). That α-methylcinnamic acid and α-acetamidocinnamic acid occupy entirely different sites on the catalyst surface was shown by product and cross-inhibition studies. The observation that dihydro-α-methyleinnamic acid increases the rate of hydrogenation of α-acetamidocinnamic acid on palladium-on-poly-S-valine indicates a possible allosteric mechanism analogous to that observed with enzyme catalysis.

Stereospecific hydrogenations using palladium-on-poly-L-leucine

Studies have been conducted concerning the stereospecific nature of catalysts prepared by depositing palladium upon a poly-L-amino acid. The poly- L -amino acid chosen for this study was poly- L -leucine which was prepared from N-carboxy- L -leucine anhydride. The substrates employed in this work were α-methylcinnamic acid and α-acetamidocinnamic acid. Hydrogenation of α-methylcinnamic acid catalyzed by palladium-on-poly- L -leucine produced predominately R(−)-dihydro-α-methylcinnamic acid and hydrogenation of α-acetamidocinnamic acid using the same catalyst produced, after hydrolysis, S(−)-phenylalanine.