ENANTIOSELECTIVE HYDROGENATION OF PYRUVIC-ACID OXIME TO ALANINE ON PDALUMINA/

The chemo- and enantioselective hydrogenation of pyruvic acid oxime ha ve been studied on Pd/alumina, the latter in the presence of the 1,2-a mino alcohol type alkaloids ephedrine, cinchonidine, and cinchonine. H igh yields of racemic alanine (90-98%) were obtained in the absence of alkaloids in polar solvents at 0-45 degrees C and 10 bar. Enantiosele ction increased with higher temperature and alkaloid:oxime molar ratio , A 1:1 ephedrine:oxime molar ratio afforded the best enantiomeric exc ess (26%). The presence of alkaloid resulted in a decrease of reaction rate by a factor of up to 140, compared to the racemic hydrogenation. Based on X-ray crystal structure analysis of the alkaloid-pyruvic aci d oxime adduct, a mechanism is proposed for the steric course of the r eaction. Extended interactions by multiple H bonds between the adsorbe d alkaloid-oxime salt units on the Pd surface is assumed to be at the origin of the moderate enantioselectivity and the very low enantiosele ctive hydrogenation rate. (C) 1996 Academic Press, Inc.