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DOI: 10.1055/s-2007-968226
Asymmetric Deprotonation Using Polymer-Supported Chiral Lithium Amides
L. Ma, P. G. Williard*
Brown University, Providence, USA
Publikationsverlauf
Publikationsdatum:
20. Februar 2007 (online)
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Significance
Polymer-supported chiral lithium amides were prepared and used as chiral bases in the asymmetric deprotonation of prochiral cyclic ketones. The reaction of Merrifield resin 1 with chiral amines 2 in the presence of NaHCO3 gave the polymer-supported amines 3a and 3b (eq. 1). The polymer-supported chiral lithium amide 3a-Li was generated in situ from amine 3a with BuLi. The deprotonation of the prochiral cyclic ketones 4 with the chiral lithium amide 3a-Li and the reaction of the resulting lithium enolates with trimethylsilyl chloride gave the trimethylsilyl enol ethers 5 in 86-94% yield with moderate enantioselectivity (31-41% ee) (eq. 2). The reaction of 6 with 3-Li gave (S)-7 with high enantioselectivity (3a: 71% ee, 3b: 81% ee) (eq. 3). The polymer-supported amine 3b was recovered and reused five times.