Asymmetric hydrogenation of aromatic ketones catalyzed by (1S,2S)-DPEN-modified Ru-PPh3/γ-Al2O3 catalyst

The asymmetric hydrogenations of acetophenone and its derivatives over the (1S,2S)-DPEN-modified Ru-PPh3/γ-Al2O3 were investigated. The effects of reaction conditions on the asymmetric hydrogenation of acetophenone are discussed in detail. The results showed that this catalyst had high activity and moderate enantioselectivity for the asymmetric hydrogenation of acetophenone and its derivatives. Under the optimum conditions, the conversion of acetophenone was up to 100%, and the enantioselectivity for the formation of (R)-phenyl ethanol was 77.7% ee. The chiral alcohol products could be easily separated by centrifugation, while the catalyst could be reused several times.

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(R)-(+)-1-PhenylethanolC8H10OEe = 77.7%[α]D24=+38.5 (c 1.12, CH2Cl2)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)

(R)-(+)-1-PhenylpropanolC9H12OEe = 78.0%[α]D24=+22.6 (c 1.23, C2H5OH)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)

(R)-(+)-1-(2′-Fluorophenyl)ethanolC8H9OFEe = 44.3%[α]D24=+21.7 (c 1.36, CHCl3)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)

(R)-(+)-1-(2′-Bromophenyl)ethanolC8H9OBrEe = 43.7%[α]D24=+29.3 (c 1.24, CHCl3)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)

(S)-(−)-1-(2′-Methoxyphenyl)ethanolC9H12O2Ee = 33.4%[α]D24=-10.3 (c 1.65, CHCl3)Source of chirality: asymmetric hydrogenationAbsolute configuration: (S)

(R)-(+)-1-(4′-Methoxyphenyl)ethanolC9H12O2Ee = 74.6%[α]D24=+38.6 (c 1.13, CHCl3)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)

(R)-(+)-1-(4′-Trifluoromethylphenyl)ethanolC9H9OF3Ee = 73.6%[α]D24=+27.5 (neat)Source of chirality: asymmetric hydrogenationAbsolute configuration: (R)