Synthesis of a new indanyl-substituted bisoxazoline ligand and applications in the enantioselective Henry reaction

In recent years, bisoxazoline ligands have been widely used as chiral ligands in metal-catalyzed asymmetric reactions. In this study, two new chiral bisoxazoline ligands with a norbornadiene backbone were synthesized in five steps 53% and 75% yields. They were then used as chiral ligands in the copper-catalyzed asymmetric Henry reaction. The reaction conditions giving the highest enantioselectivity were determined for Henry reaction. As a result of these studies, the best ligand was found to be the indanyl-substituted bisoxazoline ligand, the copper salt was Cu(Ac)2, the solvent was isopropanol, the amount of catalyst was 5% and the temperature was 15 °C. Finally, under the optimized reaction conditions, the addition of nitromethane to different aliphatic and aromatic aldehydes resulted in the formation of 13 chiral nitroaldol products with up to 91% yields and 68% enantiomeric excess.