Synthesis 2003(6): 0925-0939
DOI: 10.1055/s-2003-38695
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© Georg Thieme Verlag Stuttgart ˙ New York

Regioselective C-C Bond Formation Reactions on 2,3-Dibromo- and 2,3,5-Tribromobenzofuran­ as an Access to Multiply Substituted Benzofurans. Total Syntheses of Eupomatenoids 3, 4, 5, 6, and 15

Thorsten Bach*, Marc Bartels
Lehrstuhl für Organische Chemie I, Technische Universität München, Lichtenbergstr. 4, 85747 Garching
Fax: +49(89)28913315.; e-Mail: thorsten.bach@ch.tum.de;
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Publikationsverlauf

Received 11 February 2003
Publikationsdatum:
16. April 2003 (online)

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Abstract

Regioselective C-C-bond formation reactions at 2,3-dibromobenzofuran (1) and 2,3,5-tribromobenzofuran (6) were studied. Pd-catalyzed Sonogashira and Negishi cross-coupling occurred with perfect regioselectivity at carbon atom C-2 to provide 2-substituted 3-bromobenzofurans (12, 14) and 3,5-dibromobenzofurans (17, 18) in 50-91% yield. A regioselective displacement of the bromine substituents in 3,5-dibromobenzofurans 18 was achieved by a halogen-metal exchange reaction at carbon atom C-3 and by a Ni-catalyzed Kumada cross-coupling at C-5. The methodology was applied to the synthesis of eupomatenoids 3, 4, 5, 6, and 15 (5). The synthesis of these compounds was achieved in overall yields of up to 60%.