Kinetic and Stereochemical Analyses of Amine-Additive Effects on the Hydrogenation of α-Phenylcinnamic Acid over Cinchonidine-Modified Pd/C

Asymmetric hydrogenation of α-phenylcinnamic acid catalyzed by cinchonidine (CD)-modified palladium has been performed. Without benzylamine (BA), a modification inconsistency was observed: the rate diminished when a small amount of CD was used, whereas the product enantiomeric excess (ee) increased when substantially more CD was used. By altering the amount of amine additive, we deduced that this inconsistency was caused by the amine effect of CD itself. With a 1,8-diazabicyclo[5.4.0]undec-7-ene additive, the catalytic amount was sufficient to result in the highest ee of 81%.