Increased enantioselectivity in the presence of benzylamine in the heterogeneous hydrogenation of image-unsaturated carboxylic acids

The use of one equivalent of benzylamine increased the enantioselectivity in the heterogeneous catalytic hydrogenation of image-unsaturated carboxylic acids over cinchonidine-modified 5% Pd/Al2O3 catalyst. The beneficial effect of the amine additive was dependent on substrate structure. The highest effect, a more than sixfold increase in the enantiomeric excess, was obtained in the hydrogenation of itaconic acid. This is the first report on the enantioselective hydrogenation of a prochiral image-unsaturated dicarboxylic acid over a supported heterogeneous metal catalyst.