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J Am Chem Soc. 2006 Dec 27;128(51):17057-62.

Total synthesis of (-)-heptemerone B and (-)-guanacastepene E.

Author information

1
Department of Chemistry, University of California-Berkeley, Berkeley, CA 94720-1460, USA.

Abstract

A concise, stereoselective, and convergent total synthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple known starting materials. Our general synthetic approach integrates a diverse set of reactions, including an intramolecular Heck reaction to create one quaternary stereocenter and a cuprate conjugate addition for the establishment of the other. The central seven-membered ring was closed with an uncommon electrochemical oxidation, whereas the five-membered ring was formed through ring-closing metathesis. The absolute configuration of the two key building blocks was established through an asymmetric reduction and an asymmetric ene reaction.

PMID:
17177458
DOI:
10.1021/ja0660507
[Indexed for MEDLINE]

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