title: Total synthesis of (-)-heptemerone B and (-)-guanacastepene E.
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.
authors.affiliation: Department of Chemistry, University of California-Berkeley, Berkeley, CA 94720-1460, USA.
authors.forename: Aubry K
authors.initials: AK
authors.lastname: Miller
authors.forename: Chambers C
authors.initials: CC
authors.lastname: Hughes
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Kennedy-Smith
authors.forename: Stefan N
authors.initials: SN
authors.lastname: Gradl
authors.forename: Dirk
authors.initials: D
authors.lastname: Trauner
mesh_terms: D003500:Cyclization; D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D004224:Diterpenes; C409194:guanacastepene; C516934:heptemerone B