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Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines
Author(s) -
Denmark Scott E.,
Nakajima Noriyuki,
Stiff Cory M.,
Nicaise Olivier J.C.,
Kranz Michael
Publication year - 2008
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200800017
Subject(s) - chemistry , enantioselective synthesis , sparteine , substituent , reagent , aldimine , nucleophile , organolithium compounds , alkylation , organic chemistry , combinatorial chemistry , catalysis , ion , deprotonation
The enantioselective addition of organolithium reagents to N ‐anisylaldimines promoted by chiral bisoxazolines and (−)‐sparteine as external ligands is described. This reaction proceeds readily with a wide range of aldimine substrates (aliphatic, aromatic, olefinic) and organolithium nucleophiles (Me, n‐ Bu, Ph, vinyl) in excellent yields (81–99%) and with high enantioselectivities (up to 97:3.0 er ). The external ligands can be used in substoichiometric amounts albeit with slightly attenuated enantioselectivities. A systematic evaluation of the structural features of the bisoxazolines revealed a primary contribution from the substituent at C(4) and a secondary influence from the bridging substituents. A computational analysis (PM3) provided a clear rationalization for the origin of enantioselectivity.