Application of a Stereospecific Intramolecular Allenylsilane Imino Ene Reaction to Enantioselective Total Synthesis of the 5,11-Methanomorphanthridine Class of Amaryllidaceae Alkaloids
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- 作者：Jian Jin and Steven M. Weinreb
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：June 25, 1997
- 年：1997
- 卷：119
- 期：25
- 页码：5773 - 5784
- 全文大小：724K
- 年卷期：v.119,no.25(June 25, 1997)
- ISSN：1520-5126
文摘
Enantioselective total syntheses of the pentacyclic5,11-methanomorphanthridine Amaryllidaceaealkaloids(-)-montanine (1), (-)-coccinine (2), and(-)-pancracine (3) were accomplished using anintramolecular concertedpericyclic allenylsilane imino ene cycloaddition as a key step.These complex natural products were constructedstarting from readily available enantiomerically pure epoxy alcohol15 which was converted to allenylsilanealdehyde28 via an efficient nine-step sequence. Theimine generated from aldehyde 28 and iminophosphorane47 underwenta stereospecific thermal imino ene reaction to afford key intermediatecis aminoalkyne 49. It was possible totransformthis compound via Lindlar hydrogenation followed by anintramolecular Heck reaction to seven-membered ringtetracycle 51. This olefinic intermediate could befunctionalized through its epoxide to yield
-hydroxymethylintermediate 54, and then pentacyclic alcohol 64.Procedures were then developed to convert this material totheenantiomerically pure alkaloids 1-3. Aformal enantioselective total synthesis of (-)-brunsvigine(4) was alsoachieved via triol 72.
-hydroxymethylintermediate 54, and then pentacyclic alcohol 64.Procedures were then developed to convert this material totheenantiomerically pure alkaloids 1-3. Aformal enantioselective total synthesis of (-)-brunsvigine(4) was alsoachieved via triol 72.