New chiral amino alcohol ligands derived from 1-phenylethylamine for efficient Ru-catalyzed asymmetric transfer hydrogenation

A series of chiral amino alcohols have been prepared from cheap and readily available (S)-1-phenylethylamine through a one-step transformation. The ability of these newly developed amino alcohols as chiral ligands was evaluated in the Ru-catalyzed asymmetric transfer hydrogenation of aromatic alkyl ketones, providing chiral secondary alcohols with good to excellent conversions (71–100%) and moderate to good enantioselectivities (67–95% ee). The results also showed that the structure of these amino alcohols has a significant influence on the conversion and enantioselectivity.

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{2-[(S)-1-Aminoethyl]phenyl}methanolC9H13NOEe >98%[α]D20=-18.3 (c 0.38, ethanol)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

2-{2-[(S)-1-Aminoethyl]phenyl}propan-2-olC11H17NOEe >98%[α]D20=-3.3 (c 0.38, ethanol)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

1-{2-[(S)-1-Aminoethyl]phenyl}cyclohexanolC14H21NOEe >98%[α]D20=-73.2 (c 0.38, ethanol)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

{2-[(S)-1-Aminoethyl]phenyl}diphenylmethanolC21H21NOEe >98%[α]D20=+10.2 (c 0.35, ethanol)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)