Effective Asymmetric Hydrogenation of Itaconic Acid Catalyzed by Neutral and Cationic Rhodium(i) Complexes With Chiral Pyrrolidinodiphosphine Ligand

Asymmetric hydrogenation of itaconic acid catalyzed by neutral and cationic rhodium(I) complexes with a chiral pyrrolidinodiphosphine, BPPM, was carried out to give (S)-(−)-methylsuccinic acid with 90–92 %e.e. in excellent yield. Enantioselectivity of the reaction was found to depend upon the amounts of triethyl amine added. In the presence of triethyl amine, the neutral catalyst is suggested to be converted to the cationic species.