Diastereoselective Catalytic Hydrogenation of Schiff Bases of <i>N</i>-Pyruvoyl-(<i>S</i>)-Proline Esters

Abstract

Diastereoselective catalytic hydrogenation of pyruvic acid esters, amides, and their Schiff bases has been well studied over a long period to show that proline is one of the most effective chiral auxiliaries. Proline derivatives have been used as auxiliaries in the diastereoselective catalytic hydrogenation of pyruvamide Schiff bases. The diastereoselective hydrogenation resulted in up to a 78% enantiomeric excess of the amino acid derived from the hydrolysis of the dipeptide products. The chelation hypothesis explains the stereochemistry of the catalytic hydrogenation using (S)-proline esters in the amide moiety and the two chiral centers in the amide and Schiff base moieties.