Effects of Lithium Salts on the Enantioselectivity of Protonation of Enolates with Chiral Imide
- 1 February 1998
- journal article
- letter
- Published by Georg Thieme Verlag KG in Synlett
- Vol. 1998 (2) , 174-176
- https://doi.org/10.1055/s-1998-1594
Abstract
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)Keywords
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