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Synfacts 2014; 10(8): 0789
DOI: 10.1055/s-0034-1378388
Synthesis of Natural Products and Potential Drugs
© Georg Thieme Verlag Stuttgart · New York

Synthesis of (±)-Lundurine A and B

Contributor(s):
Erick M. Carreira
,
Christian Ebner
Arai S, Nakajima M, Nishida A * Chiba University, Japan
A Concise and Versatile Synthesis of Alkaloids from Kopsia tenuis: Total Synthesis of (±)-Lundurine A and B.

Angew. Chem. Int. Ed. 2014;
53: 5569-5572
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Publication History

Publication Date:
18 July 2014 (online)

 
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Key words

lundurines - samarium - cyclopropanation

Significance

(±)-Lundurine A and B, isolated from Kopsia tenuis, possess a highly substituted cyclopropane attached to an indoline. Previously, Nishida and co-workers described the total ­synthesis of (±)-lundurine B (Org. Lett. 2014, 16, 768; Synfacts 2014, 10, 338). Although this first approach was successful, problems arose during a transcarbamation from tert-butyl to methylcarbamate. Therefore, a second approach employing an elegant SmI2-mediated intramolecular cyclopropanation as the key step was developed.


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Comment

Propargylic alcohol C, prepared from indolinone B, was transformed into enoate D by a copper(II)-catalyzed Meyer–Schuster rearrangement. Within four steps, the methylcarbamate and the required enone were introduced. SmI2 mediated a highly stereoselective cyclopropanation of E to give F in 52% yield as a single diastereomer. Intramolecular palladium-catalyzed allylation provided amine I, which could be converted into both (±)-lundurine A and B by alkylation or acylation followed by ring-closing metathesis.


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