Synthesis 2005(9): 1459-1466  
DOI: 10.1055/s-2005-865358
PAPER
© Georg Thieme Verlag Stuttgart · New York

Radical-Mediated Synthesis of Racemic Deoxypodophyllotoxin and Related Lignans

Tanja Kolly-Kovač, Philippe Renaud*
Universität Bern, Departement für Chemie und Biochemie, Freiestrasse 3, 3012 Bern, Switzerland
Fax: +41(31)6314359; e-Mail: philippe.renaud@ioc.unibe.ch;
Further Information

Publication History

Received 11 April 2005
Publication Date:
02 May 2005 (online)

Abstract

An approach for the synthesis of lignans related to the podophyllotoxin family is reported. The key reaction is a highly dia­stereoselective iodoacetal cyclization under iodine atom transfer conditions followed by a homolytic aromatic substitution. The second aromatic ring is introduced at a later stage via addition of aryllithium to an aryl ketone. A novel and very mild method for the deoxygenation of the intermediate tertiary benzylic alcohols is described.

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The enol ether (E)-8 was prepared via Heck coupling of the piperonyloyl chloride(6) and ethyl vinyl ether, however, this reaction is low yielding. Iodoacetalization of (E)-8 with allyl alcohol and NIS afforded the diastereomer of iodoacetal 9. This approach was abandoned due to the low yield of the Heck coupling process.