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

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim High enantioselection is obtained in α-amination of acyclic β-keto esters in the presence of lanthanide triflates and pybox ligands. The Eu3+ complexes proved more active than those with Yb3+ and La3+ 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.