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

Abstract

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).