Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation-Fragmentations: Computational Modelling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C and Marilzabicycloallene D
DOI: 10.14469/hpc/1116 Metadata
Created: 2016-07-26 16:14
Last modified: 2022-08-28 07:55
License: Creative Commons: Public Domain Dedication 1.0
Funding: (none given)
Co-author: Andrew White Co-author: D. Christopher Braddock Co-author: James Clarke Co-author: Karl Bonney Co-author: Muhammad Yaqoob Co-author: Savade Solanki
Description
The total synthesis of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C and marilzabicycloallene D as halogenated C15-acetogenin twelve-membered bicyclic and tricyclic ether bromoallene-containing marine metabolites from Laurencia species are described. Two enantiomerically pure C4-epimeric dioxabicyclo[8.2.1]tridecenes were synthesised by E-selective ring-closing metathesis where their absolute stereochemistry was previously set via catalytic asymmetric homoallylic epoxidation and elaborated via regioselective epoxide-ring opening and diastereoselective bromoetherification. Epimeric face-selective oxidation of their ï12,13 olefins followed by bromoallene installation allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II & 12-epoxyobtusallene IV. Subsequent exploration of their putative biomimetic oxonium ion formation-fragmentations reactions revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X respectively. The original configurations of the substrates evidently control oxonium ion formation and their subsequent preferred mode of fragmentation by nucleophilic attack at C9 or C12. Quantum modelling of this stereoselectivity at the ωB97X-D/Def2-TZVPPD/SCRF=methanol level revealed that in addition to direction resulting from hydrogen bonding, the dipole moment of the ion-pair transition state is an important factor. Marilzabicycloallene D as a pentahalogenated twelve-membered bicyclic ether bromoallene was synthesised by a face-selective chloronium ion initiated oxonium ion formation-fragmentation process followed by subsequent bromoallene installation. Full primary/raw NMR data is available for all compounds.
Members
| DOI | Description |
|---|---|
| 10.14469/hpc/1267 | NMR data for Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation-Fragmentations: Computational Modelling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C and Marilzabicycloallene D |
| 10.14469/hpc/1919 | Computational data for Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation-Fragmentations: Computational Modelling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C and Marilzabicycloallene D |
| 10.14469/hpc/678 | 12: x-ray conformation methanol TS Def2-TZVPPD BF4 ion pair, top face |
| 10.14469/hpc/1248 | FAIR Data table. Computed relative reaction free energies (kcal/mol-1) of Obtusallene derived oxonium and chloronium cations |
| 10.14469/hpc/10062 | Relocation of Computational data for Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation-Fragmentations: Computational Modelling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C and Marilzabicycloallene D |
Associated DOIs
| Current dataset ... | DOI | Description |
|---|---|---|
| References | 10.1021/acs.joc.6b02008 | Article corresponding to these data. |
| References | 10.14469/ch/191973 | 12R-B calculated NBO analysis. Conformation taken from doi: 10.5517/ccxfjd7. Def2-TZVPPD cation only. |
| References | 10.14469/ch/191976 | oxonium cation 9...Br x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/191978 | oxonium cation 6...Br x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/191979 | oxonium cation 12...Br x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/191985 | 9...OMe x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/191986 | 12...OMe x-ray conformation methanol TS Def2-TZVPPD freq |
| References | 10.14469/ch/191988 | 6...OMe x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/191997 | 12...HOMe x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/192008 | 9...HOMe alt conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/192018 | 6...HOMe x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/192018 | 6...HOMe x-ray conformation methanol TS Def2-TZVPPD |
| References | 10.14469/ch/192024 | 9...HOMe X-ray conformation methanol TS Def2-TZVPPD |