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Christopher D Braddock - One of the best experts on this subject based on the ideXlab platform.
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epimeric face selective oxidatIons and diastereodivergent transannular Oxonium Ion formatIon fragmentatIons computatIonal modeling and total syntheses of 12 epoxyobtusallene iv 12 epoxyobtusallene ii obtusallene x marilzabicycloallene c and marilzabicycloallene d
Journal of Organic Chemistry, 2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 12-epoxyobtusallene IV. Subsequent exploratIon of their putative biomimetic Oxonium Ion formatIon–fragmentatIons reactIons revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X, respectivel...
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1 Bromonium-Ion Induced Transannular Oxonium Ion FormatIon-FragmentatIon in Model Obtusallene Systems and Structural Reassignment of Obtusallenes V-VII
2016Co-Authors: Christopher D Braddock, David S Millan, Savade Solanki, Rebecca H. Pouwer, A Pérez-fuertes, Andrew J. P. WhiteAbstract:Abstract: Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13 in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy and the positIon of the halogens at C-7 and C-13 were reassigned on the basis of a 13C NMR chlorine-induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned
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Epimeric Face-Selective OxidatIons and Diastereodivergent Transannular Oxonium Ion FormatIon FragmentatIons: ComputatIonal Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D
2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized by a face-selective chloronium Ion initiated Oxonium Ion formatIon–fragmentatIon process followed by subsequent bromoallene installatIon
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intramolecular bromonium Ion assisted epoxide ring opening capture of the Oxonium Ion with an added external nucleophile
Journal of Organic Chemistry, 2011Co-Authors: Karl J Bonney, Christopher D Braddock, Andrew J. P. White, Muhammad YaqoobAbstract:9-Oxabicyclo[6.1.0]non-4-ene (1) undergoes intramolecular bromonium Ion-assisted epoxide ring-opening using N-bromosuccinimide via a presumed Oxonium Ion that is subject to stereospecific, nonregioselective capture with added external nucleophiles producing novel bicyclo[4.2.1] and bicyclo[3.3.1] ethers. Carboxylic acids (as catalyzed by tetramethylguanidine), alcohols, water, and halides can all functIon as effective nucleophiles. Stereospecific direct opening of the bromonium Ion with carboxylic acids was found to be a competing process where high dilutIon disfavors this pathway. Halogen-induced isotopic 13C NMR shifts (Δδ CBr 1.3−1.9 ppb; Δδ CCl 8.6−8.7 ppb) were found to be most useful in unambiguously identifying halogen-bearing carbons, and correlatIon of these 13C NMR shifts allowed ready assignment of diastereomeric structures. The structure of adducts 6b, 6c, 7b, 7c, 7d, and 8a−d were all elucidated by X-ray crystallography.
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bromonium Ion induced transannular Oxonium Ion formatIon fragmentatIon in model obtusallene systems and structural reassignment of obtusallenes v vii
Journal of Organic Chemistry, 2009Co-Authors: Christopher D Braddock, David S Millan, Yolanda Perezfuertes, Savade Solanki, Richard N Sheppard, Rebecca H. Pouwer, Andrew J. P. WhiteAbstract:Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13, in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy, and the positIon of the halogens at C-7 and C-13 was reassigned on the basis of a 13C NMR chlorine induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned.
Andrew J. P. White - One of the best experts on this subject based on the ideXlab platform.
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epimeric face selective oxidatIons and diastereodivergent transannular Oxonium Ion formatIon fragmentatIons computatIonal modeling and total syntheses of 12 epoxyobtusallene iv 12 epoxyobtusallene ii obtusallene x marilzabicycloallene c and marilzabicycloallene d
Journal of Organic Chemistry, 2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 12-epoxyobtusallene IV. Subsequent exploratIon of their putative biomimetic Oxonium Ion formatIon–fragmentatIons reactIons revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X, respectivel...
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1 Bromonium-Ion Induced Transannular Oxonium Ion FormatIon-FragmentatIon in Model Obtusallene Systems and Structural Reassignment of Obtusallenes V-VII
2016Co-Authors: Christopher D Braddock, David S Millan, Savade Solanki, Rebecca H. Pouwer, A Pérez-fuertes, Andrew J. P. WhiteAbstract:Abstract: Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13 in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy and the positIon of the halogens at C-7 and C-13 were reassigned on the basis of a 13C NMR chlorine-induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned
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Epimeric Face-Selective OxidatIons and Diastereodivergent Transannular Oxonium Ion FormatIon FragmentatIons: ComputatIonal Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D
2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized by a face-selective chloronium Ion initiated Oxonium Ion formatIon–fragmentatIon process followed by subsequent bromoallene installatIon
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intramolecular bromonium Ion assisted epoxide ring opening capture of the Oxonium Ion with an added external nucleophile
Journal of Organic Chemistry, 2011Co-Authors: Karl J Bonney, Christopher D Braddock, Andrew J. P. White, Muhammad YaqoobAbstract:9-Oxabicyclo[6.1.0]non-4-ene (1) undergoes intramolecular bromonium Ion-assisted epoxide ring-opening using N-bromosuccinimide via a presumed Oxonium Ion that is subject to stereospecific, nonregioselective capture with added external nucleophiles producing novel bicyclo[4.2.1] and bicyclo[3.3.1] ethers. Carboxylic acids (as catalyzed by tetramethylguanidine), alcohols, water, and halides can all functIon as effective nucleophiles. Stereospecific direct opening of the bromonium Ion with carboxylic acids was found to be a competing process where high dilutIon disfavors this pathway. Halogen-induced isotopic 13C NMR shifts (Δδ CBr 1.3−1.9 ppb; Δδ CCl 8.6−8.7 ppb) were found to be most useful in unambiguously identifying halogen-bearing carbons, and correlatIon of these 13C NMR shifts allowed ready assignment of diastereomeric structures. The structure of adducts 6b, 6c, 7b, 7c, 7d, and 8a−d were all elucidated by X-ray crystallography.
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bromonium Ion induced transannular Oxonium Ion formatIon fragmentatIon in model obtusallene systems and structural reassignment of obtusallenes v vii
Journal of Organic Chemistry, 2009Co-Authors: Christopher D Braddock, David S Millan, Yolanda Perezfuertes, Savade Solanki, Richard N Sheppard, Rebecca H. Pouwer, Andrew J. P. WhiteAbstract:Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13, in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy, and the positIon of the halogens at C-7 and C-13 was reassigned on the basis of a 13C NMR chlorine induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned.
David S Millan - One of the best experts on this subject based on the ideXlab platform.
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epimeric face selective oxidatIons and diastereodivergent transannular Oxonium Ion formatIon fragmentatIons computatIonal modeling and total syntheses of 12 epoxyobtusallene iv 12 epoxyobtusallene ii obtusallene x marilzabicycloallene c and marilzabicycloallene d
Journal of Organic Chemistry, 2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 12-epoxyobtusallene IV. Subsequent exploratIon of their putative biomimetic Oxonium Ion formatIon–fragmentatIons reactIons revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X, respectivel...
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1 Bromonium-Ion Induced Transannular Oxonium Ion FormatIon-FragmentatIon in Model Obtusallene Systems and Structural Reassignment of Obtusallenes V-VII
2016Co-Authors: Christopher D Braddock, David S Millan, Savade Solanki, Rebecca H. Pouwer, A Pérez-fuertes, Andrew J. P. WhiteAbstract:Abstract: Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13 in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy and the positIon of the halogens at C-7 and C-13 were reassigned on the basis of a 13C NMR chlorine-induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned
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Epimeric Face-Selective OxidatIons and Diastereodivergent Transannular Oxonium Ion FormatIon FragmentatIons: ComputatIonal Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D
2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized by a face-selective chloronium Ion initiated Oxonium Ion formatIon–fragmentatIon process followed by subsequent bromoallene installatIon
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bromonium Ion induced transannular Oxonium Ion formatIon fragmentatIon in model obtusallene systems and structural reassignment of obtusallenes v vii
Journal of Organic Chemistry, 2009Co-Authors: Christopher D Braddock, David S Millan, Yolanda Perezfuertes, Savade Solanki, Richard N Sheppard, Rebecca H. Pouwer, Andrew J. P. WhiteAbstract:Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13, in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy, and the positIon of the halogens at C-7 and C-13 was reassigned on the basis of a 13C NMR chlorine induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned.
Savade Solanki - One of the best experts on this subject based on the ideXlab platform.
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epimeric face selective oxidatIons and diastereodivergent transannular Oxonium Ion formatIon fragmentatIons computatIonal modeling and total syntheses of 12 epoxyobtusallene iv 12 epoxyobtusallene ii obtusallene x marilzabicycloallene c and marilzabicycloallene d
Journal of Organic Chemistry, 2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 12-epoxyobtusallene IV. Subsequent exploratIon of their putative biomimetic Oxonium Ion formatIon–fragmentatIons reactIons revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X, respectivel...
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1 Bromonium-Ion Induced Transannular Oxonium Ion FormatIon-FragmentatIon in Model Obtusallene Systems and Structural Reassignment of Obtusallenes V-VII
2016Co-Authors: Christopher D Braddock, David S Millan, Savade Solanki, Rebecca H. Pouwer, A Pérez-fuertes, Andrew J. P. WhiteAbstract:Abstract: Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13 in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium-Ion induced transannular Oxonium Ion formatIon-fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy and the positIon of the halogens at C-7 and C-13 were reassigned on the basis of a 13C NMR chlorine-induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned
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Epimeric Face-Selective OxidatIons and Diastereodivergent Transannular Oxonium Ion FormatIon FragmentatIons: ComputatIonal Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D
2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized by a face-selective chloronium Ion initiated Oxonium Ion formatIon–fragmentatIon process followed by subsequent bromoallene installatIon
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bromonium Ion induced transannular Oxonium Ion formatIon fragmentatIon in model obtusallene systems and structural reassignment of obtusallenes v vii
Journal of Organic Chemistry, 2009Co-Authors: Christopher D Braddock, David S Millan, Yolanda Perezfuertes, Savade Solanki, Richard N Sheppard, Rebecca H. Pouwer, Andrew J. P. WhiteAbstract:Ring-closing metathesis was used to construct the strained 11-membered ring of obtusallenes II (and IV). Bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon gave the macrocyclic carbon skeleton of obtusallene VII with a bromine atom at C-13, in line with a previously published hypothesis. An additIonal brominated [5.5.1]bicyclotridecane adduct that must arise from a bromonium Ion induced transannular Oxonium Ion formatIon−fragmentatIon could also be isolated, suggesting that this adduct represents the core of an as yet undiscovered natural product. An authentic sample of obtusallene V was studied by NMR spectroscopy, and the positIon of the halogens at C-7 and C-13 was reassigned on the basis of a 13C NMR chlorine induced isotopic shift. This revised structure was subsequently confirmed by X-ray crystallography. These findings allow us to confidently conclude that the structures of obtusallenes VII and VI should also be reassigned.
Muhammad Yaqoob - One of the best experts on this subject based on the ideXlab platform.
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epimeric face selective oxidatIons and diastereodivergent transannular Oxonium Ion formatIon fragmentatIons computatIonal modeling and total syntheses of 12 epoxyobtusallene iv 12 epoxyobtusallene ii obtusallene x marilzabicycloallene c and marilzabicycloallene d
Journal of Organic Chemistry, 2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 12-epoxyobtusallene IV. Subsequent exploratIon of their putative biomimetic Oxonium Ion formatIon–fragmentatIons reactIons revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X, respectivel...
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Epimeric Face-Selective OxidatIons and Diastereodivergent Transannular Oxonium Ion FormatIon FragmentatIons: ComputatIonal Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D
2016Co-Authors: James Clarke, David S Millan, Savade Solanki, Karl J Bonney, Muhammad Yaqoob, Andrew J. P. White, Henry S. Rzepa, Christopher D BraddockAbstract:The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 Δ12,13 olefins followed by bromoallene installatIon allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized by a face-selective chloronium Ion initiated Oxonium Ion formatIon–fragmentatIon process followed by subsequent bromoallene installatIon
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intramolecular bromonium Ion assisted epoxide ring opening capture of the Oxonium Ion with an added external nucleophile
Journal of Organic Chemistry, 2011Co-Authors: Karl J Bonney, Christopher D Braddock, Andrew J. P. White, Muhammad YaqoobAbstract:9-Oxabicyclo[6.1.0]non-4-ene (1) undergoes intramolecular bromonium Ion-assisted epoxide ring-opening using N-bromosuccinimide via a presumed Oxonium Ion that is subject to stereospecific, nonregioselective capture with added external nucleophiles producing novel bicyclo[4.2.1] and bicyclo[3.3.1] ethers. Carboxylic acids (as catalyzed by tetramethylguanidine), alcohols, water, and halides can all functIon as effective nucleophiles. Stereospecific direct opening of the bromonium Ion with carboxylic acids was found to be a competing process where high dilutIon disfavors this pathway. Halogen-induced isotopic 13C NMR shifts (Δδ CBr 1.3−1.9 ppb; Δδ CCl 8.6−8.7 ppb) were found to be most useful in unambiguously identifying halogen-bearing carbons, and correlatIon of these 13C NMR shifts allowed ready assignment of diastereomeric structures. The structure of adducts 6b, 6c, 7b, 7c, 7d, and 8a−d were all elucidated by X-ray crystallography.
