New chiral bis(oxazolinyl)bipyridine ligand (bipymox): Enantioselection in the asymmetric hydrosilylation of ketones

A homochiral chiral 6,6′-bis(oxazolinyl)-2,2′-bipyridine ligand, bipymox (1), and its rhodium complex were synthesized to examine the enantioselectivity in the asymmetric hydrosilylation of ketones in comparison to other chiral oxazoline ligands such as bis-(oxazolinyl)pyridine, pybox(2), and mono(oxazolinyl)pyridine, pymox(3). The bipymox-rhodium catalyst gave the (S)-absolute configuration of the product 1-phenylethanol (90 %ee) in the reduction of acetophenone with diphenylsilane the same as the pybox-rhodium system but opposite to the pymox-rhodium system. The reduction of 4-tert-butylcyclohexanone was also described.