title: Concise substrate-controlled asymmetric total syntheses of dioxabicyclic marine natural products with 2,10-dioxabicyclo-[7.3.0]dodecene and 2,9-dioxabicyclo[6.3.0]undecene skeletons.
abstract: We report a completely substrate-controlled approach to the asymmetric total synthesis of representative dioxabicyclic bromoallene marine natural products with either a 2,10-dioxabicyclo[7.3.0]dodecene or 2,9-dioxabicyclo[6.3.0]undecene skeleton from commercially available glycidol as a common starting material. The former include (-)-isolaurallene (1), the enantiomeric form of natural (+)-neolaurallene (2), and (+)-itomanallene A (3c), and the latter are (+)-laurallene (4) and (+)-pannosallene (5a). In addition, our first syntheses of 3c and 5a established the structure and absolute stereochemistry of both natural products. Our general approach to establish the α,α'-relative stereochemistry of the medium-ring (oxonene or oxocene) and tetrahydrofuran, respectively, involved the judicious pairing of our protecting-group-dependent intermolecular amide enolate alkylation (either chemoselective chelation-controlled or dianion alkylation) with either our intramolecular amide enolate or nitrile anion alkylation. Remarkable selectivity was achieved through the use of the appropriate alkylation steps, and this approach offered us optional access to any of these dioxabicyclic bromoallene marine natural products. In addition, a computational analysis was performed to investigate conformational effects on the rate of oxonene formation via RCM, a key step in these approaches. The results suggested an alternative rationale for reactivity based on the avoidance of eclipsing torstional interactions in the AS2-type ring conformation.
authors.affiliation: The Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 151-742, Korea.
authors.forename: Mi Jung
authors.initials: MJ
authors.lastname: Kim
authors.forename: Te-ik
authors.initials: TI
authors.lastname: Sohn
authors.forename: Deukjoon
authors.initials: D
authors.lastname: Kim
authors.forename: Robert S
authors.initials: RS
authors.lastname: Paton
mesh_terms: D001688:Biological Products / Q000138:chemical synthesis* / Q000737:chemistry; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D001688:Biological Products; D019086:Bridged Bicyclo Compounds, Heterocyclic