New Enantioselective Chiral Imidazolidine Liands for Pd-Catalazed Asymmetric Allylic Alkylation

摘要

During the last decade, various enantioselective catalysts have been developed for palladium-catalyzed allylic substitution reactions. In particular, chiral phosphinooxazoline ligands are one of the effective ligands in this reaction. The design of efficient chiral ligands is essential for asymmetric allylic alkylation (AAA) and has become one of the most intense areas of investigation. A series of C_2-symmetric diphosphines such as chiraphos, DIOP and BINAP, which gave high enantioselectivities in asymmetric hydrogenation, have been used in early study. However, in contrast with five-membered oxazolines, the chiral imidazolines or imidazolidines have not been extensively studied as ligands to date. Because the combination of an imidazolidine group with an auxiliary donor atom provides the different electronic and sterie environment around the metal, we have prepared new ligands containing both the imidazolidine moiety and an auxiliary S or P donor.