Design of Heterogeneous Organocatalyst for the Asymmetric Michael Addition of Aldehydes to Maleimides

Asymmetric Michael additions of isobutyraldehyde to maleimides catalyzed by optically pure diamines and their sulfonamides were investigated to develop heterogeneous chiral catalysts for these reactions. Encouraging results, i.e. complete transformations and optically pure products, were obtained using para-toluenesulfonamide or methanesulfonamide derivatives. Chiral solid materials were prepared by covalent bonding of the diamines on sulfonyl chloride functionalized supports. Immobilization of the amines was confirmed by FT-IR spectroscopy. The heterogeneous catalyst prepared by bonding optically pure 1,2-diphenylethane-1,2-diamine to polystyrene support was highly enantioselective, giving results approaching those obtained using soluble sulfonamide derivatives. The anchored catalyst was recyclable few times keeping its activity followed by gradual small decrease in conversion, however, still providing high, up to 97%, enantiomeric excesses. These materials are among the first efficient recyclable catalysts used in the enantioselective Michael addition of aldehydes to maleimides.