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Dynamic resolution of N-alkyl-2-lithiopyrrolidines with the chiral ligand (−)-sparteine
Authors:Iain Coldham  Samuel Dufour  Graham P Vennall
Institution:a Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
b Department of Chemistry, University of Exeter, Stocker Road, Exeter EX4 4QD, UK
Abstract:A selection of 2-lithiopyrrolidines with different N-alkyl-substituents were prepared and tested for their dynamic resolution in the presence of the chiral ligand (−)-sparteine. Good yields of the electrophile-quenched products were obtained with enantiomer ratios up to 85:15 using branched N-alkyl derivatives. The major product was shown to have the opposite absolute configuration compared with that obtained in the asymmetric deprotonation of N-Boc-pyrrolidine with (−)-sparteine. The enantioselectivity arises from a dynamic thermodynamic resolution in which the minor diastereomeric complex reacts faster with the electrophile.
Keywords:Organolithiums  Tin-lithium exchange  Dynamic resolution  Asymmetric induction  (&minus  )-Sparteine
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