Catalytic asymmetric transfer hydrogenation of ketones using terpene-based chiral β-amino alcohols

Catalytic asymmetric transfer hydrogenations of aromatic alkyl ketones have been studied using [RuCl2(p-cymeme)]2 and terpene-based β-amino alcohols. The limonene derived amino alcohol, (1S,2S,4R)-1-methyl-4-(1-methylethenyl)-2-(methylamino)cyclohexanol gave the most promising results. Chiral secondary alcohols were obtained in good to excellent yields and moderate enantioselectivities (up to 71%).

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{(S)-1-[(1S,2S,5R)-2-Hydroxy-2-methyl-5-(1-methylethenyl)cyclohexylcarbamoyl]-2-methylpropyl}-carbamic acid tert-butyl esterC20H36N2O4[α]D25=+18.1 (c 2.0, methanol)Source of chirality: asymmetric synthesisAbsolute configuration: (1S,1′S,2′S,5′R)

1-tert-Butyl-3-[(1S,2S,5R)-2-hydroxy-2-methyl-5-(1-methylethenyl)cyclohexyl]ureaC15H28N2O2[α]D25=+22.4 (c 2.0, methanol)Source of chirality: asymmetric synthesisAbsolute configuration: (1S,2S,5R)

1-[(1S,2S,5R)-2-Hydroxy-2-methyl-5-(1-methylethenyl)cyclohexyl]-3-phenylureaC17H24N2O2[α]D25=+9.7 (c 2.0, methanol)Source of chirality: asymmetric synthesisAbsolute configuration: (1S,2S,5R)

[(1S,2S,5R)-2-Hydroxy-2-methyl-5-(1-methylethenyl)cyclohexyl]carbamic acid isobutyl esterC15H27NO3[α]D25=+13.5 (c 1.0, methanol)Source of chirality: asymmetric synthesisAbsolute configuration: (1S,2S,5R)