Asymmetric transfer hydrogenation reductions using tethered ruthenium (II) catalysts

摘要

By asymmetric transfer hydrogenation, substituted quinolines, which are generally regarded as challenging substrates for reduction, were successfully converted into tetrahydroquinolines using "tethered" Ru(II) and "tethered" Rh(III) complexes in formic acid/triethylamine. An ether-linked "tethered" catalyst was successfully synthesized through a sequence that avoids the use of a Birch reduction for the formation of a 1,4-cyclohexadiene moiety. The ether link is incorporated between the basic amine of the ligand and the η6- arene ring, giving results comparable to the alkyl-"tethered" complexes. N-alkylated complexes containing a straight-chain substituent attached to a hydroxyl, ether or ester function can act as effective catalysts for the reduction of ketones, and also contains the required functionality for attachment of the catalyst to a heterogeneous support.