title: Total syntheses of ent-heliespirones A and C.
abstract: Stereodivergent total syntheses of ent-heliespirone A and C were both completed in 11 vessels and ∼24% combined overall yield (A + C). These syntheses employed an identical inverse demand Diels-Alder reaction between a surrogate for an extendedly conjugated γ-δ unsaturated ortho-quinone methide and L-lactic-acid-derived exocyclic enol ether. Novel reactions of special note include a diastereoselective reduction of a chroman spiroketal by combination of borontrifluoride etherate and triethyl silane, along with oxidative rupture of a chroman etherial ring into the corresponding p-quinone by argentic oxide (AgO). In addition, an unusual intramolecular etherification of a 3° alcohol caused by cerium ammonium nitrate was observed.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106, United States.
authors.forename: Wen-Ju
authors.initials: WJ
authors.lastname: Bai
authors.forename: Jason C
authors.initials: JC
authors.lastname: Green
authors.forename: Thomas R R
authors.initials: TR
authors.lastname: Pettus
mesh_terms: D016227:Benzoquinones / Q000138:chemical synthesis*; D002839:Chromans / Q000737:chemistry*; D003500:Cyclization; D045563:Indolequinones / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011809:Quinones / Q000737:chemistry*; D012717:Sesquiterpenes / Q000138:chemical synthesis*; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D016227:Benzoquinones; D002839:Chromans; D045563:Indolequinones; D011809:Quinones; D012717:Sesquiterpenes; D012821:Silanes; C552388:heliespirone A; C520941:heliespirone C; C512918:triethylsilane; C068040:quinone methide