Synthesis and computation of diastereomeric phenanthroline-quinine ligands and their application in asymmetric Henry reaction

A class of chiral ligands has been developed by combining phenanthroline with quinine in a one-step method that does not require resolution. The synthesized three ligands were then coordinated with Cu-(II) and the performance of the resultant chiral catalysts in the asymmetric Henry reaction was evaluated. Moderate to good yields (up to 86%) with high enantioselectivities (up to 99% ee) were observed in the reactions catalyzed by one of the three catalysts. Theoretical calculations were performed to analyze the catalytic activities of the different Cu-(II)-ligand catalysts. Three different ligands were investigated and one ligand was found to adopt an unexpected five-coordinated mode; the second coordinated with two nitrogen atoms of phenanthroline to give a complex, which activated both substrates of Henry reaction; the third was unable to form a complex with Cu-(II). (C) 2013 Elsevier Ltd. All rights reserved.