Biphasic Glycerol/2-MeTHF, Ruthenium-Catalysed Enantioselective Transfer Hydrogenation of Ketones Using Sodium Hypophosphite as Hydrogen Donor

Abstract : Sodium hypophosphite has been used as an efficient hydrogen donor in the transfer hydrogenation of aliphatic and aromatic ketones in the presence of [RuCl2(p-cymene)]2 and 2,2′-bipyridine in water. The corresponding alcohols were isolated in moderate to excellent yields (39–95 %). Good chemoselectivity was observed with ester, nitrile and halide functionalities in the ketones not being reduced. An enantioselective version of the reaction using [RuCl(p-cymene){(R,R)-TsDPEN}] as catalyst in a glycerol/2-MeTHF biphasic solvent mixture has been developed and allowed the reduction of (hetero)aromatic ketones with excellent chemo- and enantioselectivities (up to 97 % ee).