Asymmetric cyclopropanation catalyzed by C2-symmetric bi(oxazolines)

C2-symmetric bi(oxazolines) 3a–e were prepared in three steps based on a tartaric-derived vicinal diamine as common precursor. These chiral ligands were studied with respect to their directive influence on the enantioselective copper catalyzed cyclopropanation of 1,1-diphenylethylene and styrene. The highest enantioselectivities (79% ee) were achieved with bi(oxazoline) 3e, bearing bulky adamantyl groups even using commercial CuOTf. The presence of desiccants such as molecular sieves or magnesium sulfate was found to be crucial for high yields and reproducibility.