The coupling of enantiomerically enriched amines with aryl bromides produces the corresponding N-aryl derivatives. The choice of ligand in the palladium-catalyzed coupling is critical to the formation of the anilines without loss of enantiomeric purity. While LnPd (L = P(o-tolyl)3) successfully catalyzes the intramolecular aryl amination of α-subsituted optically pure amines, intermolecular coupling reactions with this catalyst system gives racemized products. In contrast, intermolecular N-arylations employing LnPd (L = (±)-BINAP) gives products in good yields with no erosion of enantiopurity. A mechanism for the observed racemization is proposed. The utility of the intramolecular process is demonstrated by the synthesis of 5, an intermediate in the formal synthesis of 6, a potent ACE inhibitor.
“Palladium-Catalyzed Coupling of Optically Active Amines with Aryl Bromides”, J. Am. Chem. Soc., 1997, 119(36), 8451-8458.