Cyclic amino acid salts as catalysts for the asymmetric Michael reaction

Different chiral cyclic amino acid alkali metal and ammonium salts were used as catalysts for the asymmetric Michael addition of aldehydes to nitrostyrene. The reaction yield and stereoselectivity depend slightly on the salt cation. The highest yield of the reaction (up to 100%) was obtained with (S)-morpholine-3-carboxylic acid salts, which gave moderate to good enantioselectivities (up to 72% ee) and diastereoselectivities (dr up to 89:11) whereas the highest selectivity was obtained with proline sodium salt (ee 88%).

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(3S)-Benzyl 4-benzylmorpholine-3-carboxylateC19H21NO3[α]D20=-71.7 (c 3.8, EtOH)Source of chirality: (S)-serineAbsolute configuration: (3S)

(3S)-Morpholine-3-carboxylic acid lithium saltC5H8NO3Li[α]D22=-21.3 (c 5.8, H2O)Source of chirality: (S)-serineAbsolute configuration: (3S)

(3S)-Morpholine-3-carboxylic acid sodium saltC5H8NO3Na[α]D20=-23.9 (c 3.4, H2O)Source of chirality: (S)-serineAbsolute configuration: (3S)

(3S)-Morpholine-3-carboxylic acid potassium saltC5H8NO3K[α]D25=-16.4 (c 5.3, H2O)Source of chirality: (S)-serineAbsolute configuration: (3S)

(3S)-Morpholine-3-carboxylic acid caesium saltC5H8NO3Cs[α]D25=-12.3 (c 5.3, H2O)Source of chirality: (S)-serineAbsolute configuration: (3S)

(3S)-Morpholine-3-carboxylic acid tetrabutyl ammonium saltC21H44N2O3[α]D20=-15.0 (c 1.0, H2O)Source of chirality: (S)-serineAbsolute configuration: (3S)

(2S)-Piperazine-2-carboxylic acid sodium saltC5H9N2O2Na[α]D20=-6.4 (c 1.7, H2O)Source of chirality: (S)-2-piperazinecarboxylic acid dihydrochlorideAbsolute configuration: (2S)