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Synlett 1998; 1998(2): 174-176
DOI: 10.1055/s-1998-1594
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Effects of Lithium Salts on the Enantioselectivity of Protonation of Enolates with Chiral Imide

Akira Yanagisawa* , Tetsuo Kikuchi, Hisashi Yamamoto
  • *Graduate School of Engineering, Nagoya University, CREST, Japan Science and Technology Corporation (JST), Chikusa, Nagoya 464-01, Japan
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Publikationsdatum:
31. Dezember 2000 (online)

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An increase in enantioselectivity was observed in the asymmetric protonation of prochiral enolates with a chiral imide using lithium salt as an additive. For example, (R)-enriched 2-n-pentylcyclopentanone 6 was obtained in high yield with 90% ee when the silyl enol ether 4 was treated with n-BuLi in the presence of 5 equiv of LiBr in Et2O and the resulting lithium enolate 5 was then protonated by a solution of (S,S)-imide 1 in THF. In contrast, the product 6 obtained without LiBr exhibited a lower enantiomeric excess (74% ee)

enantioselective protonation - lithium enolates - chiral imide - 2-oxazoline - lithium salts