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Hydrogenation of acetamidocinnamates

Brunner et al. [26] synthesized and applied so-called dendrizymes in enan-tioselective catalysis. These catalysts are based on dendrimers which have a functionalized periphery that carries chiral subunits, (e.g. dendrons functionalized with chiral menthol or borneol ligands). The core phosphine donor atoms can be complexed to (transition) metal salts. The resultant dendron-enlarged 1,2-diphosphino-ethane (e.g. 16, see Scheme 17) Rh1 complexes were used as catalysts in the hydrogenation of acetamidocinnamic acid to yield iV-acetyl-phenylalanine (Scheme 17) [26]. A small retardation of the hydrogenation of the substrate was encountered, pointing to an effect of the meta-positioned dendron substituents. No significantly enantiomerically enriched products were isolated. However, a somewhat improved enantioselectivity (up to 10-11% e.e.) was... [Pg.501]

Chauvin et al. reported the asymmetric hydrogenation of acetamidocinnamic acid to (S)-phenylalanine with a cationic chiral rhodium catalyst in [C4-mim][SbF6] ionic liquid, more recently the 2-arylacryhc acid has been produced with a reasonable 64% yield using a chiral ruthenium catalysts in [C4-mim][BF4] ionic hquids. Palladium catalysts immobilized in an ionic liquid-polymer gel membrane containing either [C2-mim][CF3S03] or [C2-mim][BF4] have also been reported as catalysts for heterogeneous hydrogenation reactions. [Pg.1470]

The same catalyst showed higher ee values approaching 90% in the hydrogenation of acetamidocinnamic and methylenesuccinic acids in aqueous solutions, which is still somewhat less than those obtained with standard BINAP [163]. A new approach to the immobilization of the catalyst utilized a technique similar to the supported aqueous phase method. Sulfonate surfactant residues were tailored to the surface of silica, thus providing a layer capable... [Pg.208]

FIGURE 22.13 Rhodium complexes investigated in the hydrogenation of acetamidocinnamic acid and keto-pantolactone. [Pg.544]

Figure C2.7.4. Catalytic cycle for hydrogenation of methyl-(Z)-a-acetamidocinnamate tire rate constants were measured at 298 K S is solvent [8],... Figure C2.7.4. Catalytic cycle for hydrogenation of methyl-(Z)-a-acetamidocinnamate tire rate constants were measured at 298 K S is solvent [8],...
Figure C2.7.5. Pathways for tire hydrogenation of metliyl-(Z)-a-acetamidocinnamate catalysed by a rhodium comolex witli a chiral diohosohine lieand S is solvent 181. Figure C2.7.5. Pathways for tire hydrogenation of metliyl-(Z)-a-acetamidocinnamate catalysed by a rhodium comolex witli a chiral diohosohine lieand S is solvent 181.
Asymmetric synthesis is a method for direct synthesis of optically active amino acids and finding efficient catalysts is a great target for researchers. Many exceUent reviews have been pubHshed (72). Asymmetric syntheses are classified as either enantioselective or diastereoselective reactions. Asymmetric hydrogenation has been appHed for practical manufacturing of l-DOPA and t-phenylalanine, but conventional methods have not been exceeded because of the short life of catalysts. An example of an enantio selective reaction, asymmetric hydrogenation of a-acetamidoacryHc acid derivatives, eg, Z-2-acetamidocinnamic acid [55065-02-6] (6), is shown below and in Table 4 (73). [Pg.279]

Table 4. Asymmetric Hydrogenation of (Z)-2-Acetamidocinnamic Acid (6) to (f -At-Acetylphenylalanine (7)... Table 4. Asymmetric Hydrogenation of (Z)-2-Acetamidocinnamic Acid (6) to (f -At-Acetylphenylalanine (7)...
Chira.lHydrogena.tion, Biological reactions are stereoselective, and numerous dmgs must be pure optical isomers. Metal complex catalysts have been found that give very high yields of chiral products, and some have industrial appHcation (17,18). The hydrogenation of the methyl ester of acetamidocinnamic acid has been carried out to give a precusor of L-dopa, ie, 3,4-dihydroxyphenylalanine, a dmg used in the treatment of Parkinson s disease. [Pg.165]

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. [Pg.270]

Encapsulated rhodium complexes were prepared from Rh-exchanged NaY zeolite by complexation with (S)-prolinamide or M-tert-butyl-(S)-prolinamide [73,74]. Although these catalysts showed higher specific activity than their homogeneous counterparts in non-enantioselective hydrogenations, the hydrogenation of prochiral substrates, such as methyl (Z)-acetamidocinnamate [73] or ( )-2-methyl-2-pentenoic acid [74], led to low... [Pg.184]

For example, the hydrogenation of methyl (Z)-a-acetamidocinnamate gives a chiral product when conducted in the presence of a chiral diphosphine catalyst. The enantiomeric excess data for micro-reactor and batch operation are in line when performed imder similar conditions [169]. A very high reproducibility of determining data on enantiomeric excess was reported [170]. In addition, the ee distribution was quite narrow 90% of aU ee data were within 40-48% [170]. [Pg.73]

Conjugated Alkene Hydrogenation Investigated in Micro Reactors Cas/liquid reaction 19 [CL 19) Hydrogenation of Z-(a)-acetamidocinnamic methyl ester... [Pg.632]

Scheme 8.5 Hydrogenation of methyl a-acetamidocinnamate with S/P ligands derived from carbohydrates. Scheme 8.5 Hydrogenation of methyl a-acetamidocinnamate with S/P ligands derived from carbohydrates.
An especially important case is the enantioselective hydrogenation of a-amidoacrylic acids, which leads to a-aminoacids.29 A particularly detailed study has been carried out on the mechanism of reduction of methyl Z-a-acetamidocinnamate by a rhodium catalyst with a chiral diphosphine ligand DIPAMP.30 It has been concluded that the reactant can bind reversibly to the catalyst to give either of two complexes. Addition of hydrogen at rhodium then leads to a reactive rhodium hydride and eventually to product. Interestingly, the addition of hydrogen occurs most rapidly in the minor isomeric complex, and the enantioselectivity is due to this kinetic preference. [Pg.380]

Fig. 5.4. Schematic mechanism for enantioselective hydrogenation of methyl acetamidocinnamate (MAC) over a cationic ruthenium catalyst. Reproduced... Fig. 5.4. Schematic mechanism for enantioselective hydrogenation of methyl acetamidocinnamate (MAC) over a cationic ruthenium catalyst. Reproduced...
The cationic [Ir(cod)(bnda)](BF4) complex (bnda = 2,2 -diamno-l,l -binaphthyl), (336), catalyzes the enantioselective hydrogenation of (Z)-a-acetamidocinnamic acid to acetamidodihydrocinnamic... [Pg.208]

Brunner et al. attached chiral branches to non-chiral catalytically active sites. With the aim to influence the enantioselectivity of transition metal catalyzed reactions they synthesized several dendritically enlarged diphosphines such as 81 [101] (Fig. 29). In situ prepared catalysts from [Rh(cod)Cl]2and81 have been tested in the hydrogenation of (a)-N-acetamidocinnamic acid. After 20 hours at 20 bar H2-pressure (Rh/substrate ratio 1 50) the desired product was obtained with an enantiomer ratio of 51 49. [Pg.166]

A new class of phosphines (30) containing only an axial element of chirality (atropisomerism) has been made (253, 254). An in situ 1 1 rhodium/2,2-bis(diphenylphosphinomethyl)-1,1 -binaphthyl system (30a) hydrogenated a-acetamidocinnamic acid to a 54% ee (S) using 50 atm H2, the solvent not being recorded (253). The corresponding diphenyl-phosphinite system (30b) in toluene-acetone was particularly effective (76% ee) for hydrogenation (95 atm) of a-acetamidocinnamic and a-acet-amidoacrylic esters (254). [Pg.349]

Although the latter product is a solvated mononuclear [Rh(MeOH)2(diphos)]+ cation, in the solid state it is isolated as a binuclear complex of formula [Rh2 (diphos)2](BF4)2, in which each rhodium center is bonded to two phosphorus atoms of a chelating bis(diphenylphosphino)ethane ligand, and to a phenyl ring of the bis(diphenylphosphino)ethane ligand of the other rhodium atom. This dimer reverts to a mononuclear species on redissolving. The mechanism of hydrogenation of the prochiral alkene methyl(Z)-a-acetamidocinnamate, studied in detail by Halpern [31], is depicted in Scheme 1.7. [Pg.17]

Borner reported the synthesis of pyrophosphites 149 with chiral binaphthyl substituents [118]. The results showed that the Hg-binaphthyl unit was the best for the Rh-catalyzed hydrogenation of methyl (Z)-2-acetamidocinnamate (48% ee) and dimethyl itaconate (70% ee). [Pg.981]

In 1982, Yamashita reported the application of L-talopyranoside-based phos-phine-phosphinite ligand 165 (Fig. 27.15), and found that it induced low enan-tioselectivity (4.7-13% ee) in the hydrogenation of a-acetamidocinnamic acid [119]. Reetz introduced the phosphine-phosphonite ligand (151-153), which led to moderate enantioselectivity (52-88% ee) in the Rh-catalyzed hydrogenation of dimethyl itaconate [120]. The binaphthyl unit remained an essential element in the system. [Pg.981]

Pizzano and Suarez described a convenient preparation of a series of new chiral phosphine-phosphites based on the easy demethylation of o-anisyl phosphines [124]. Rh-156a complex was found to be the most effective catalyst for the hydrogenation of dimethyl itaconate (99.6% ee), whereas 155b and 156a induced >99% ee in the hydrogenation of methyl N-2-acetamidocinnamate. Reetz... [Pg.981]


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See also in sourсe #XX -- [ Pg.11 ]




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Asymmetric Catalytic Hydrogenation of a-Acetamidocinnamic Acid Esters

Hydrogenation of -2-acetamidocinnamic acid

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