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
π-stacking between the pentafluorophenyl and the naphthalene
rings. In particular, access to enantiopure ligand (S,S,Ra)-2a was realized by fractional
crystallization of the corresponding ∼3:1 atropdiastereomeric
mixture. The preliminary application of ligand (S,S,Ra)-UCD-PHIM showed excellent activities
in the enantioselective copper-catalyzed A3 coupling (ee’s
up to 98.1% and yields up to 98%).