Asymmetric organocatalyzed Michael addition of aldehydes to β-nitrostyrene in ionic liquids

The addition of aliphatic aldehydes to β-nitrostyrene, catalyzed by proline-derived organocatalysts, proceeded well in various ionic liquids. Products were obtained in high yields and syn/anti diastereoselectivity. However, the enantioselectivity was only mediocre, even though some analogous reactions in organic solvents were highly enantioselective. We also evaluated the temperature effect on the diastereoselectivity as well as on the enantioselectivity of the Michael addition.

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(2R,3S)-2-Isopropyl-4-nitro-3-phenylbutanalC13H17NO3[α]D = +16.5 (c 0.77, CHCl3) 30% eeSource of chirality: asymmetric catalysisAbsolute configuration: (2R,3S)

(2R,3S)-2-Methyl-4-nitro-3-phenylbutanalC11H13NO3[α]D = +8.2 (c 1.0, CHCl3) 19% eeSource of chirality: asymmetric catalysisAbsolute configuration: (2R,3S)

(2R,3S)-2-Ethyl-4-nitro-3-phenylbutanalC12H15NO3[α]D = +6.8 (c 1.1, CHCl3) 20% eeSource of chirality: asymmetric catalysisAbsolute configuration: (2R,3S)

(R)-2,2-Dimethyl-4-nitro-3-phenylbutanalC12H15NO3[α]D = +3.2 (c 1.0, CHCl3) 30% eeSource of chirality: asymmetric catalysisAbsolute configuration: (R)