Diastereofacial π-Stacking as an Approach To Access an Axially Chiral P,N-Ligand for Asymmetric Catalysis

A phosphino-imidazoline (PHIM) ligand possessing axial chirality is prepared in a straightforward five-step synthesis. Configurational stability around the chiral axis is achieved by the diastereofacial pi-stacking between the pentafluorophenyl and the naphthalene rings. In particular, access to enantiopure ligand (S,S,R-a)-2a was realized by fractional crystallization of the corresponding similar to 3:1 atropdiastereomeric mixture. The preliminary application of ligand (S,S,R-a)-UCD-PHIM showed excellent activities in the enantioselective copper-catalyzed A3 coupling (ee's up to 98.1% and yields up to 98%).