Highly enantioselective hydrogenation of N-aryl imines derived from acetophenones by using Ru-pybox complexes under hydrogenation or transfer hydrogenation conditions in isopropanol

Abstract

The asymmetric reduction of N-aryl imines derived from acetophenones by using Ru complexes bearing both a pybox (2,6-bis(oxazoline)pyridine) and a monodentate phosphite ligand has been described. The catalysts show good activity with a diverse range of substrates, and deliver the amine products in very high levels of enantioselectivity (up to 99 %) under both hydrogenation and transfer hydrogenation conditions in isopropanol. From deuteration studies, a very different labeling is observed under hydrogenation and transfer hydrogenation conditions, which demonstrates the different nature of the hydrogen source in both reactions.

Keywords: amines; asymmetric catalysis; hydrogenation; ruthenium; transfer hydrogenation.