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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
Author(s) -
Pericas Àlex,
Jiménez Rubén,
Granados Albert,
Shafir Alexandr,
Vallribera Adelina,
Roglans Anna,
Molins Elies
Publication year - 2016
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201600820
Subject(s) - chemistry , lanthanide , enantioselective synthesis , amination , trifluoromethanesulfonate , europium , ternary operation , electrophilic amination , steric effects , ligand (biochemistry) , medicinal chemistry , electrophile , organic chemistry , combinatorial chemistry , catalysis , ion , biochemistry , receptor , computer science , programming language
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.