Asymmetric Catalytic Hydrogenations of <i>N</i>-Pyruvoyl-(<i>S</i>)-proline Esters

Abstract

Abstract Asymmetric catalytic hydrogenations of the entitled compounds were carried out over palladium on charcoal in various solvents to afford N-[(S)-lactoyl]-(S)-proline esters with a d.e.(=diastereoisomeric excess) of up to 59%. The stereochemistry of the catalytic hydrogenation was explained by the “chelation mechanism.” And the effects of temperature and bulkiness of the ester groups on the asymmetric induction were also described.