Journal
TETRAHEDRON
Volume 69, Issue 15, Pages 3264-3273Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2013.02.035
Keywords
Total synthesis; One-pot; Lithium; Asymmetric reaction; Heterocycles
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Funding
- JSPS
- JST
- Grants-in-Aid for Scientific Research [24590035, 23790029, 24106719, 24790011] Funding Source: KAKEN
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Chiral diether-mediated asymmetric aminolithiation of indolylpropenoate with lithium amide in toluene at -78 degrees C for 15 min gave, after aqueous ammonium chloride quench, the corresponding conjugate addition product with 97% ee in 89% yield. If hydrogen chloride in methanol was selected as a quencher, however, aminolithiation at -78 degrees C for 3 h gave the corresponding adduct with 97% ee in 54% yield, along with recovery of the starting enoate in 39% yield. Based on this finding of an incomplete and slow reaction at -78 degrees C, the aminolithiation conditions were optimized to be at -60 degrees C for 15 h and subsequent enolate trap with alkyl halide upon an addition of DMPU afforded the desired aminoalkylation product with 98% ee in 89% yield. Further approach toward total synthesis of (-)-kopsinine was carried out by examining asymmetric aminolithiation with N-hydroxyethylamine equivalent, one-pot piperidine formation, and Claisen condensation. (C) 2013 Elsevier Ltd. All rights reserved.
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