Atroposelective Transfer Hydrogenation of Biaryl Aminals via Dynamic Kinetic Resolution. Synthesis of Axially Chiral Diamines

An
efficient dynamic kinetic resolution (DKR) approach for the
synthesis of axially chiral diamines has been developed on the basis
of a ruthenium-catalyzed enantioselective transfer hydrogenation.
The strategy relies on the configurational instability of cyclic biaryl
aminal precursors in equilibrium with their amino-imine open forms,
as supported by DFT calculations. This protocol features a broad substrate
scope of aliphatic amines and biaryl scaffolds and proceeds under
very mild conditions, allowing the preparation of BINAM homologues
in good to high yields and nearly perfect enantioselectivities (up
to 99% ee).