Simultaneous Access to Two Enantio-enriched Alcohols by a Single Ru-Catalyst: Asymmetric Hydrogen Transfer from Racemic Alcohols to Matching Ketones

Oxidative kinetic resolution and asymmetric transfer
hydrogenation
are two classical methods to access chiral secondary alcohols. Described
here is an example of cross asymmetric hydrogen transfer between H-donor
racemic alcohols and H-acceptor prochiral ketones, which merge these
two approaches in one catalytic cycle that could afford two chiral
alcohols simultaneously. To create a large equilibrium constant for
driving the reversible processes into completion, H-donor alcohols
and H-acceptor ketones should have substituents with significantly
different properties in sterics or electronics, yet this would cause
a substantial challenge for a single catalyst to induce high ee’s
for both alcohols. Moreover, either enantiomer of a racemic alcohol
could be obtained via sequential transfer hydrogenations with a single
Ru-catalyst. These results collectively provide efficient access to
two distinct enantio-enriched alcohols as well as both enantiomers
of single alcohols.