Lanthanides–pybox: An Excellent Combination for Highly Enantioselective Electrophilic α‐Amination of Acyclic β‐Keto Esters. Isolation of Ternary Pybox/Ln/β‐Keto Ester Complexes

Abstract

High enantioselection is obtained in α‐amination of acyclic β‐keto esters in the presence of lanthanide triflates and pybox ligands. The Eu
3+
complexes proved more active than those with Yb
3+
and La
3+
and high dependence of
ee
on the type and steric bulk of the ester group was observed. Excellent results were achieved using a combination of europium triflate with ligand
L4
(diphenyl‐pybox). Preparation of ternary complexes (
8
) [(
L4
)(β‐keto ester enolate)Ln (OTf)
2
] was accomplished. Complexes
8
and [(
L4
)(β‐keto ester)Ln (OTf)
2
]
+
, identified by ESI‐MS, are proposed as key intermediates of the α‐amination reaction.