Lanthanide complexes combined with chiral salen ligands: application in the enantioselective epoxidation reaction of α,β-unsaturated ketones.

Readily available lanthanide amides Ln[N(SiMe 3 ) 2 ] 3 (Ln = Nd (1), Sm (2), Eu (3), Yb (4), La (5)), combined with chiral salen ligands H 2 L a (( S , S )- N , N '-di-(3,5-disubstituted-salicylidene)-1,2-cyclohexanediamine) and H 2 L b (( S , S )- N , N '-di-(3,5-disubstituted-salicylidene)-1,2-diphenyl-1,2-ethanediamine) were employed in the enantioselective epoxidation of α,β-unsaturated ketones. It was found that the salen-La complex shows the highest efficiency and enantioselectivity. A relatively broad scope of α,β-unsaturated ketones was investigated, and excellent yields (up to 99%) and moderate to good enantioselectivities (37-87%) of the target molecules were achieved.