Asymmetric hydrogenation of a-acetamido cinnamic acid

In a dry box, a 25 mL Schlenk-type flask with a magnetic stirring bar was charged with Rh(COD)[(S,S)-3-Pt-FerroPHOS] BF4 (9.9 mg), a-aceta-mido cinnamic acid (205 mg) and degassed ethanol (3.3 mL). After sealing, the flask was removed from the dry box. 

With stirring of the mixture at 20-23 °C, the flask was then freeze pumpu thaw-degassed (3 cycles) and stirred under hydrogen gas (ca. 1 bar) for 2 hours. 

The enantiomeric excess (98.9%) was determined by GC (Chrompack Chiralsil-L-Val column) 

The reaction depends on various factors including solvent, initial pressure, catalyst precursor and the N-protecting group. Due to the high stability of (S,S)-3-Pt-FerroPHOS towards air, it may be used in an industrial process. 

The cylindrically chiral diphosphine neither changed, nor lost its reactivity and selectivity in hydrogenation reactions even after long exposure to air. In a 31P-NMR study, no detectable air-oxidation was observed even after a long exposure (3 weeks) to the atmosphere. The procedures for the synthesis of the chiral ligand and the asymmetric reaction described above are very simple, giving high enan-tioselectivity with many dehydroamino acids (Table 12.4). 

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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)... 

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