Asymmetric cyclopropanation catalyzed by C-2-symmetric bi(oxazolines)

C-2-symmetric bi(oxazolines) 3a-e were prepared in three steps based on a t artaric-derived vicinal diamine as common precursor. These chiral ligands w ere studied with respect to their directive influence on the enantioselecti ve 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 presenc e of desiccants such as molecular sieves or magnesium sulfate was found to be crucial for high yields and reproducibility. (C) 2000 Elsevier Science L td. All rights reserved.