The catalytic properties of L-proline for the asymmetric Michael addition of unmodified aldehydes or ketones with nitroalkenes in ionic liquid were studied. The Michael adduct from the reaction of cyclohexanone to β-nitrostyrene was determined to have a syn of (1R,2S) configuration by X-ray crystallographic analysis, which indicated that the β-nitrostyrene would be attacked from its Re-face by an enamine intermediate in accorded with an amine-catalyzed mechanism. L-Proline exhibited good catalytic properties in ionic liquid 1-n-hexyl-3-methyl imidazolium chloride, and the Michael adducts were obtained with over 89% yield and up to 70% ee through 3～5 h at room temperature. The L-proline/ionic liquid system could be easily separated and used repeatedly at least six times without much loss of reactivity.

Key words: L-proline, ionic liquid, asymmetric Michael reaction, aldehyde, ketone, nitroalkene