Enantioselective hydrogenation of propenoic acids bearing heteroaromatic substituents over cinchonidine modified Pd/alumina

The hydrogenation of two 2,3-diarylpropenoic acids bearing heteroaromatic substituents, i.e. (E)-2-phenyl-3-(2-furyl)propenoic acid and (E)-2-(3-pyridyl)-3-phenylpropenoic acid was studied over cinchonidine modified Pd catalyst for the first time. The 2-furyl substituted compound was selectively hydrogenated to 2-phenyl-3-(2-furyl)propionic acid in the presence of cinchonidine in up to 73% ee. The hydrogenation of the acid bearing 3-pyridyl substituent afforded lower ee as compared to (E)-2,3-diphenylpropenoic acid, reaching up to 61% in presence of benzylamine additive. The differences in the results were assumed to be due to the different adsorption strengths and modes of these acids and deviations in their interactions with the adsorbed modifier.