Abstract
(Chemical Equation Presented) Reactions of substituted acetone derivatives with acrylic acid esters (>200 mol %) in the presence of t-BuOK (200 mol %) in t-BuOH-THF (1:1 by volume) turned out to proceed as a cascade process consisting of the first Michael addition, the second Michael addition, and the last Claisen reaction to afford 4,4-disubstituted cyclohexane-1,3-diones. Only more substituted enolates play the role of a Michael donor in this cascade process, and therefore the ketone took up two alkoxycarbonylethyl groups on the same carbon bearing more substituents. Such intermediates were followed by intramolecular Claisen reactions leading to cyclohexane-1,3-diones bearing quaternary stereogenic centers at C(4), which bears an alkoxycarbonylethyl group and the substituent of the starting acetone derivatives. Thus-obtained 4,4-disubstituted cyclohexane-1,3-diones were successfully employed for total syntheses of intricate alkaloids of biological interest such as (+)-aspidospermidine, (±)-galanthamine, (±)-lycoramine, and (±)-mesembrine, all featuring quaternary stereogenic centers. DFT calculations provided us with clear-cut explanations for the observed chemoselectivity of the cascade process involving ketone-based enolates under thermodynamically controlled conditions.
| Original language | English |
|---|---|
| Pages (from-to) | 7498-7508 |
| Number of pages | 11 |
| Journal | Journal of Organic Chemistry |
| Volume | 73 |
| Issue number | 19 |
| DOIs | |
| Publication status | Published - Oct 3 2008 |
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ASJC Scopus subject areas
- Organic Chemistry
Cite this
Domino double Michael-Claisen cyclizations : A powerful general tool for introducing quaternary stereocenters at C(4) of cyclohexane-1,3-diones and total synthesis of diverse families of sterically congested alkaloids. / Ishikawa, Teruhiko; Kudo, Kazuhiro; Kuroyabu, Ken; Uchida, Satoshi; Kudoh, Takayuki; Saito, Seiki.
In: Journal of Organic Chemistry, Vol. 73, No. 19, 03.10.2008, p. 7498-7508.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Domino double Michael-Claisen cyclizations
T2 - A powerful general tool for introducing quaternary stereocenters at C(4) of cyclohexane-1,3-diones and total synthesis of diverse families of sterically congested alkaloids
AU - Ishikawa, Teruhiko
AU - Kudo, Kazuhiro
AU - Kuroyabu, Ken
AU - Uchida, Satoshi
AU - Kudoh, Takayuki
AU - Saito, Seiki
PY - 2008/10/3
Y1 - 2008/10/3
N2 - (Chemical Equation Presented) Reactions of substituted acetone derivatives with acrylic acid esters (>200 mol %) in the presence of t-BuOK (200 mol %) in t-BuOH-THF (1:1 by volume) turned out to proceed as a cascade process consisting of the first Michael addition, the second Michael addition, and the last Claisen reaction to afford 4,4-disubstituted cyclohexane-1,3-diones. Only more substituted enolates play the role of a Michael donor in this cascade process, and therefore the ketone took up two alkoxycarbonylethyl groups on the same carbon bearing more substituents. Such intermediates were followed by intramolecular Claisen reactions leading to cyclohexane-1,3-diones bearing quaternary stereogenic centers at C(4), which bears an alkoxycarbonylethyl group and the substituent of the starting acetone derivatives. Thus-obtained 4,4-disubstituted cyclohexane-1,3-diones were successfully employed for total syntheses of intricate alkaloids of biological interest such as (+)-aspidospermidine, (±)-galanthamine, (±)-lycoramine, and (±)-mesembrine, all featuring quaternary stereogenic centers. DFT calculations provided us with clear-cut explanations for the observed chemoselectivity of the cascade process involving ketone-based enolates under thermodynamically controlled conditions.
AB - (Chemical Equation Presented) Reactions of substituted acetone derivatives with acrylic acid esters (>200 mol %) in the presence of t-BuOK (200 mol %) in t-BuOH-THF (1:1 by volume) turned out to proceed as a cascade process consisting of the first Michael addition, the second Michael addition, and the last Claisen reaction to afford 4,4-disubstituted cyclohexane-1,3-diones. Only more substituted enolates play the role of a Michael donor in this cascade process, and therefore the ketone took up two alkoxycarbonylethyl groups on the same carbon bearing more substituents. Such intermediates were followed by intramolecular Claisen reactions leading to cyclohexane-1,3-diones bearing quaternary stereogenic centers at C(4), which bears an alkoxycarbonylethyl group and the substituent of the starting acetone derivatives. Thus-obtained 4,4-disubstituted cyclohexane-1,3-diones were successfully employed for total syntheses of intricate alkaloids of biological interest such as (+)-aspidospermidine, (±)-galanthamine, (±)-lycoramine, and (±)-mesembrine, all featuring quaternary stereogenic centers. DFT calculations provided us with clear-cut explanations for the observed chemoselectivity of the cascade process involving ketone-based enolates under thermodynamically controlled conditions.
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U2 - 10.1021/jo801316s
DO - 10.1021/jo801316s
M3 - Article
VL - 73
SP - 7498
EP - 7508
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 19
ER -