A-acetamido cinnamic acid

The reaction was followed by chiral GC (SE 30, 220 °C, nitrogen mobile phase). R (a-acetamido cinnamic acid) 3.70 min Rt (/V-acetyl-L-phenyl-alanine) 5.4 min. 

A glass liner of a 50 mL hydrogenation bomb was charged with a-acetamido cinnamic acid (240 mg) and a magnetic stirrer bar. The bomb was then assembled, flushed five times with hydrogen (the bomb was pressurized at 200 psi, then the gas inlet was closed before the hydrogen was slowly vented off). 

Other ligands were synthesis by the same methods using different chlor-ophosphines. The reduction reaction of the a-acetamido cinnamic acid gave good results in term of enantiomeric excess and yield (all the reactions went to completion). The results are summarised in Table 12.2. 

Table 12.2 Enantiomeric excess resulting from the reduction of a-acetamido cinnamic acid by rhodium (B[3.2.0]DPO) complexes.

C4C1im][PF6] [Rh(cod)(Et-DuPHOS)]+ a-Acetamido cinnamic acid 5-100 bar, 20°C /PrOH as co-solvent ee-value dependent on hydrogen concentration in the ionic liquid significant decrease in activity after the fourth cycle due to leaching influence ofH2-pressure studied. [7]... 

The procatalyst [Rh(cod)Cl]2 is an orange, air-stable solid which is commercially available, accessible in one step from RhCls and 1,5-cyclooctadiene [82], The cocatalyst DIOP (Figure 3), the most frequently used optically active phosphine, is also commercially available. A survey of the literature shows that more than half of the numerous studies on the hydrogenation of (Z)-a-acetamido-cinnamic acid have been carried out with in-situ catalysts [79, 81]. 

In another example de Souza and Dupont studied the asymmetric hydrogenation of a-acetamido cinnamic acid and the kinetic resolution of ( )-methyl-3-hydroxy-2-methylenebutanoate with chiral Rh(I) and Ru(ii) complexes in [BMIM][BF4] and [BMIM][PFs] [106]. A special focus oftheir work was on the influence of H2 pressure on conversion. They determined the hydrogen solubility in the ionic liquid using... 

Asymmetric hydrogenation of a-acetamido cinnamic acid [Rh(PNNP)(NBD)], a chiral complex L-Phenylalanine Fiorini and Giongo (1979)... 

A minor product of this Diels-Alder addition turned out to be a highly hydrophilic ligand, giving good results in rhodium-catalyzed hydrogenation of the model substrate (Z)-a-(A-acetamido)cinnamic acid. On the other hand, the major 6-substituted adducts were much less efficient due to additional chelation of the rhodium atom by the phosphonate oxygen [20]. 

Fig. 7. From Beamer et al [83] Proposed scheme for the stereospecific hydrogenation catalyzed by palladium-on-poly-(L)-leucine (a) of a-Methylcinnamic acid (b) of a-acetamido-cinnamic acid. In both cases the hydrogen should be viewed as entering the molecule Cis and from the catalytic surface, i.e., the hydrogen attack is in a direction from out of the page and toward the side away from the viewer.

In the asymmetric hydrogenation of the methyl ester of a-acetamido cinnamic acid, 3.24 cannot be observed by conventional NMR techniques. In situ PHIP-NMR studies in contrast do show two hydride signals at -19 and -2 ppm. Using a C-enriched substrate, the coupling between the asterisk-labeled carbon and the hydride at -2 ppm can also be observed. Based on the NMR data, the actual structure is concluded to be more like 3.25 than 3.24. 

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