Elsevier

Tetrahedron

Volume 45, Issue 19, 1989, Pages 6113-6126
Tetrahedron

Preparation of 5-bromotetronates [4-alkoxy-5-bromo-2(5H)-furanones] and a new concept for the synthesis of aflatoxins and related structure types. Tributyltin hydride versus palladium-promoted intramolecular hydroarylation.

Dedicated in Honor of Günther Ohloff on the Occasion of his 65th Birthday, July 21, 1989
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Abstract

The coupling of suitably functionalized o-iodophenols (e.g. 6) with 4-alkoxy-5-bromo-2(5H)-furanones (5-bromotetronates) (10a-e) gave precyclic aflatoxin M1 A-C building blocks (7, 14, 17c). Two cyclization modes for obtaining the ABC-moiety were investigated and compared. Whereas the Bu3SnH-induced reaction worked well for simple model compounds, it failed for the more functionalized compounds. The palladium-mediated procedure allowed the synthesis of potential aflatoxin M1 precursors such as 18c. An improved procedure for obtaining O-alkylated tetronates (9a-g) is described. The tetronates were converted into 5-bromotetronates (10a-e, h) under controlled free radical conditions. For example, the narthogenin precursor 10a was prepared to the exclusion of undesired isomer 11, in 62% yield. Finally, other benzoannulated heterodiquinanes, e.g. a desoxyeserolin precursor 24, were obtained by both cyclization procedures in good to excellent yield.

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Abstracted in part from a lecture delivered at the International Symposium on Agricultural and Biological Aspects of Aflatoxin Related Health Hazards, New Dehli, India, March 22–25, 1989.

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