Oxazolinylferrocene ligands for the addition of diethylzinc to benzaldehyde: Effects of the symmetry and the substituent on the oxazoline ring of theligands on asymmetric catalysis

Several tetrasubstituted oxazolinylferrocene ligands were prepared, and wit h these ligands, up to 97% chemical yield and 93% ee were afforded in asymm etric alkylation of benzaldehyde with diethylzinc. It was found that the C- 2-symmetric ligands afforded almost the same enantioselectivity but differe nt catalytic activity with their diastereomer, C-1-symmetric ligands, in th is test reaction. The bulkiness of the substituent on the oxazoline ring ha s significant effect on the enantioselectivity and particularly on catalyti c activity. These effects of the symmetry and the bulkiness of the substitu ent on the oxazoline ring of the ligands on asymmetric catalysis have been rarely reported. A plausible mechanism is proposed.