Co-Metal-Free Enantioselective Conjugate Addition Reactions of Zinc Reagents

Asymmetric conjugate addition of diethylzine to cinnamaldehyde in a co-metal-free fashion by using N,O-ligands with planar and central chirality is described. Different modulations of the ligand structure, including several combinations of the chiral units. indicate that a [2.2]paracyclophane backbone is essential for the activity and the enantioselectivity of the generated active catalyst. By using the optimized ligand, an isolated yield of 90% was obtained with up to 99% ee.