Enantioselective hydrogenation of fluorinated unsaturated carboxylic acids over cinchona alkaloid modified palladium catalysts

Abstract

The hydrogenation of trifluoromethyl substituted prochiral α,β-unsaturated carboxylic acids has been studied over cinchona alkaloid modified palladium heterogeneous catalysts. Low enantioselectivities were obtained in the hydrogenation of all three test compounds, 2-trifluoromethylacrylic acid, 4,4,4-trifluoro-3-methyl-2-butenoic acid and (E)-4,4,4-trifluoro-3-phenyl-2-butenoic acid, respectively. Significant increase in the enantioselectivity, up to 43%, was obtained in the hydrogenation of 4,4,4-trifluoro-3-methyl-2-butenoic acid by using benzylamine as additive. The presented results showed for the first time the possibility of enantioselective hydrogenation of α-unsubstituted β-disubstituted α,β-unsaturated carboxylic acids in the cinchonidine modified palladium catalytic system, that resulted in optically enriched saturated acids having the chiral center in β position. © 2007 Elsevier B.V. All rights reserved.