A new family of chiral bimetallic catalysts is applied to the direct conjugate addition of ketones or esters to a,b-unsaturated imides. The addition products possess useful functionality for the synthesis of important structural motifs found in drugs and biologically active natural products. The catalysts are screened with a series of mental pairs and ligand substitutions to optimize reactivity. Direct addition methods are attractive because many existing enantioselective addition reactions require at least one starting material to be converted to a reactive precursor prior to addition. Any method which accomplishes the same transformation without the need for a special precursor would be inherently more efficient (and more cost effective for the manufacture of pharmaceuticals). Direct conjugate addition methodology is then applied to the total synthesis of taiwanschirin C, a natural product with activity against hepatoma, colon, cancer, and cervical cancer.
