Synlett 2006(15): 2383-2386  
DOI: 10.1055/s-2006-949622
LETTER
© Georg Thieme Verlag Stuttgart · New York

Syntheses of Highly Substituted Furan and Pyrrole Derivatives via Lithiated 3-Aryl-1-methoxyallenes: Application to the Synthesis of Codonopsinine

Morshed Alam Chowdhury, Hans-Ulrich Reissig*
Institut für Chemie und Biochemie, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany
Fax: +49(30)83855367; e-Mail: hans.reissig@chemie.fu-berlin.de;
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Publication History

Received 16 June 2006
Publication Date:
08 September 2006 (online)

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Abstract

Lithiated 1-methoxy-3-phenylallenes were generated in situ from a phenyl-substituted propargylic ether. They smoothly combined with aldehydes, ketones, or imines to give allenyl adducts, which cyclized to highly substituted heterocycles either under basic conditions or with silver nitrate assistance. Analogously, a dihydropyrrole derivative was obtained by the addition of ­anisyl-substituted lithiated methoxyallene derivative to an N-tosyl imine and subsequent cyclization of the intermediate. The two diaste­reomers obtained were subsequently transformed into the alkaloid (±)-codonopsinine and one of its epimers. The key steps of these ­sequences are highly diastereoselective hydroborations of silyl enol ethers quantitatively leading to hydroxylated intermediates.