Asymmetric Michael Addition of Malonate Anions to Prochiral Acceptors Catalyzed by l-Proline Rubidium Salt

l-Proline rubidium salt catalyzes the asymmetric Michael addition of malonate anions to prochiral enones and enals. This method can be applied to a wide range of substrates to give adducts with a predictable absolute configuration: (S)-adducts from (E)-enones/enals and (R)-adducts from cyclic (Z)-enones. Both the secondary amine moiety and the carboxylate moiety are critical for the catalytic activity and asymmetric induction. Varying the countercation also affects the reaction course. High enantiomeric excesses were attained when di(tert-butyl) malonate was added to (E)-enones in the presence of CsF. The stereochemistry of the Michael reaction indicates that asymmetric induction takes place via enantioface discrimination involving the acceptor α-carbon atom rather than the β-carbon atom.