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Andrew J. P. White - One of the best experts on this subject based on the ideXlab platform.
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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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An enantiospecific polyene cyclization initiated by an enantiomerically pure Bromonium ion.
Chirality, 2013Co-Authors: D. Christopher Braddock, Jared S. Marklew, Kevin Michael Foote, Andrew J. P. WhiteAbstract:Dimethylaluminum triflate-mediated activation of tetrafluorobenzoates of enantiomerically pure bromohydrins results in enantiospecific polyene cyclizations. The initiation of cyclization by enantiomerically pure Bromonium ions and subsequent propagation is not subject to catastrophic erosion of enantiomeric purity by any intramolecular or intermolecular Bromonium ion-to-alkene transfer. Chirality 25:692–700, 2013. © 2013 Wiley Periodicals, Inc.
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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.
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The generation and trapping of enantiopure Bromonium ions
Chemical communications (Cambridge England), 2009Co-Authors: D. Christopher Braddock, Rebecca H. Pouwer, Stephen A. Hermitage, Lilian Kwok, Joanna M. Redmond, Andrew J. P. WhiteAbstract:Enantiopure Bromonium ions may be generated from enantiopure bromohydrins and derivatives, they can be trapped with an in situnucleophile to give enantiomerically pure products.
Cinzia Chiappe - One of the best experts on this subject based on the ideXlab platform.
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solvent effects on the chemistry of Bromonium and β bromocarbenium ions as reactive intermediates
ACS symposium series, 2007Co-Authors: Cinzia ChiappeAbstract:The ability of solvent to influence the rate of formation and subsequent evolution of the Bromonium ion or the β-bromocarbenium ion as key ionic intermediates formed by bromine addition to alkenes are discussed based on kinetic and stereochemical studies as well as theoretical investigations.
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The first intermediates in the bromination of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane, combination of experiments and theoretical results
Journal of Molecular Modeling, 2006Co-Authors: Cinzia Chiappe, Dieter Lenoir, Christian Silvio Pomelli, Carsten WattenbachAbstract:Bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane ( 1 ) and adamantylideneadamantane (Ad=Ad) are two caged olefins with closely related structures at the double bond. Both compounds react instantaneously with Br_2 in chlorinated hydrocarbon solvents to give mixtures of olefin–Br_2 aggregates identified as the 1:1 π-complex and Bromonium tribromide, Bromonium pentabromide ion pairs. The stoichiometry, formation constants and the electronic spectra of all the species present at equilibrium (π-complex and Bromonium ions), obtained by addition of bromine to alkene 1 , have been determined in 1,2-dichloroethane at 25° C and compared with the values that characterize the corresponding aggregates arising from Ad=Ad. The absence of the two bridging CH_2 groups in 1 significantly affects all the formation constants. Moreover, at variance with Ad=Ad, olefin 1 reacts with bromine to give, depending on reagent concentration, a substitution product. DFT (B3LYP) and ONIOM computations of 1:1 Br_2–olefin complexes for 1 and Ad=Ad confirm that the association energy is larger for the complex 1 –Br_2. The higher stability of this species seems to be correlated to the greater IP of 1 with respect to Ad=Ad which is able to compensate the reduced polarizability. The experimental value of the formation constant found for the complex 1 –Br_2, 643 vs 289 M^−1 further supports the primary role exerted by dispersion interactions in alkene-Br_2 π-complexes. Figure Geometry and evolution of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane-Br_2 complex
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The first intermediates in the bromination of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane, combination of experiments and theoretical results.
Journal of molecular modeling, 2005Co-Authors: Cinzia Chiappe, Dieter Lenoir, Christian Silvio Pomelli, Carsten WattenbachAbstract:Bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane (1) and adamantylideneadamantane (Ad=Ad) are two caged olefins with closely related structures at the double bond. Both compounds react instantaneously with Br2 in chlorinated hydrocarbon solvents to give mixtures of olefin-Br2 aggregates identified as the 1:1 pi-complex and Bromonium tribromide, Bromonium pentabromide ion pairs. The stoichiometry, formation constants and the electronic spectra of all the species present at equilibrium (pi-complex and Bromonium ions), obtained by addition of bromine to alkene 1, have been determined in 1,2-dichloroethane at 25 degrees C and compared with the values that characterize the corresponding aggregates arising from Ad=Ad. The absence of the two bridging CH2 groups in 1 significantly affects all the formation constants. Moreover, at variance with Ad=Ad, olefin 1 reacts with bromine to give, depending on reagent concentration, a substitution product. DFT (B3LYP) and ONIOM computations of 1:1 Br2-olefin complexes for 1 and Ad=Ad confirm that the association energy is larger for the complex 1-Br2. The higher stability of this species seems to be correlated to the greater IP of 1 with respect to Ad=Ad which is able to compensate the reduced polarizability. The experimental value of the formation constant found for the complex 1-Br2, 643 vs 289 M(-1) further supports the primary role exerted by dispersion interactions in alkene-Br2 pi-complexes.
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Synthesis and characterization of the syn-Bromonium ion of 4-equ chloroadamantylidenadamantane, towards a chiral bromination reagent
Tetrahedron Letters, 2004Co-Authors: Dieter Lenoir, Norbert Hertkorn, Cinzia ChiappeAbstract:Synthesis and characterization of the stable Bromonium ion of 4-equ-chloroadamantylideneadamantane is described. 13C and 1H NMR spectroscopy reveal preferred formation of the syn-isomer, which might be used as chiral bromination reagent using resolved starting material.
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What is the nature of the first-formed intermediates in the electrophilic halogenation of alkenes, alkynes, and allenes?
Chemistry (Weinheim an der Bergstrasse Germany), 2003Co-Authors: Dieter Lenoir, Cinzia ChiappeAbstract:The pi complexes first formed as essential intermediates from alkenes, alkynes, and allenes with bromine have been investigated in different solvents by UV-spectroscopy in combination with stopped-flow techniques allowing the determination of the equilibrium constants, K(f). Using alkenes with sterically protected double bonds, such as di-tert-butylstilbene and tetraneopentylethylene, the reaction stops at the stage of the 1:1 and 1:2 pi complex of the alkene with bromine as persistent species in 1,2-dichlorethane as solvent. Calculations by state-of-art ab initio and DFT methods reproduces the experimentally determined thermodynamic values quite well, and reveal the preferred structures and nature of both complexes for ethene, ethyne, and allene. Consideration of the entropy term reveals that complexes are stabilized in solution owing to reduction of the entropy loss by restricted translations and rotation. According to calculations these species are Mulliken-outer-type complexes with no or little charge transfer from bromine to the double or triple bond, respectively. The 1:2 complex has a close structural relationship to the Bromonium- or bromirenium ion, which is the subsequent intermediate on the reaction coordinate. Steric influences show a strong effect on the K(f) value, which can be explained by the polarizibility of the parent system. Addition-elimination often occurs. In bromination of adamantylidenadamantane and its derivatives the reaction stops at the stage of the Bromonium ion. The effect of various polar groups situated in equatorial homoallyl positions on the stability of corresponding pi complex and Bromonium ion has been studied in this series.
Dieter Lenoir - One of the best experts on this subject based on the ideXlab platform.
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The first intermediates in the bromination of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane, combination of experiments and theoretical results
Journal of Molecular Modeling, 2006Co-Authors: Cinzia Chiappe, Dieter Lenoir, Christian Silvio Pomelli, Carsten WattenbachAbstract:Bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane ( 1 ) and adamantylideneadamantane (Ad=Ad) are two caged olefins with closely related structures at the double bond. Both compounds react instantaneously with Br_2 in chlorinated hydrocarbon solvents to give mixtures of olefin–Br_2 aggregates identified as the 1:1 π-complex and Bromonium tribromide, Bromonium pentabromide ion pairs. The stoichiometry, formation constants and the electronic spectra of all the species present at equilibrium (π-complex and Bromonium ions), obtained by addition of bromine to alkene 1 , have been determined in 1,2-dichloroethane at 25° C and compared with the values that characterize the corresponding aggregates arising from Ad=Ad. The absence of the two bridging CH_2 groups in 1 significantly affects all the formation constants. Moreover, at variance with Ad=Ad, olefin 1 reacts with bromine to give, depending on reagent concentration, a substitution product. DFT (B3LYP) and ONIOM computations of 1:1 Br_2–olefin complexes for 1 and Ad=Ad confirm that the association energy is larger for the complex 1 –Br_2. The higher stability of this species seems to be correlated to the greater IP of 1 with respect to Ad=Ad which is able to compensate the reduced polarizability. The experimental value of the formation constant found for the complex 1 –Br_2, 643 vs 289 M^−1 further supports the primary role exerted by dispersion interactions in alkene-Br_2 π-complexes. Figure Geometry and evolution of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane-Br_2 complex
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The first intermediates in the bromination of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane, combination of experiments and theoretical results.
Journal of molecular modeling, 2005Co-Authors: Cinzia Chiappe, Dieter Lenoir, Christian Silvio Pomelli, Carsten WattenbachAbstract:Bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane (1) and adamantylideneadamantane (Ad=Ad) are two caged olefins with closely related structures at the double bond. Both compounds react instantaneously with Br2 in chlorinated hydrocarbon solvents to give mixtures of olefin-Br2 aggregates identified as the 1:1 pi-complex and Bromonium tribromide, Bromonium pentabromide ion pairs. The stoichiometry, formation constants and the electronic spectra of all the species present at equilibrium (pi-complex and Bromonium ions), obtained by addition of bromine to alkene 1, have been determined in 1,2-dichloroethane at 25 degrees C and compared with the values that characterize the corresponding aggregates arising from Ad=Ad. The absence of the two bridging CH2 groups in 1 significantly affects all the formation constants. Moreover, at variance with Ad=Ad, olefin 1 reacts with bromine to give, depending on reagent concentration, a substitution product. DFT (B3LYP) and ONIOM computations of 1:1 Br2-olefin complexes for 1 and Ad=Ad confirm that the association energy is larger for the complex 1-Br2. The higher stability of this species seems to be correlated to the greater IP of 1 with respect to Ad=Ad which is able to compensate the reduced polarizability. The experimental value of the formation constant found for the complex 1-Br2, 643 vs 289 M(-1) further supports the primary role exerted by dispersion interactions in alkene-Br2 pi-complexes.
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Synthesis and characterization of the syn-Bromonium ion of 4-equ chloroadamantylidenadamantane, towards a chiral bromination reagent
Tetrahedron Letters, 2004Co-Authors: Dieter Lenoir, Norbert Hertkorn, Cinzia ChiappeAbstract:Synthesis and characterization of the stable Bromonium ion of 4-equ-chloroadamantylideneadamantane is described. 13C and 1H NMR spectroscopy reveal preferred formation of the syn-isomer, which might be used as chiral bromination reagent using resolved starting material.
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What is the nature of the first-formed intermediates in the electrophilic halogenation of alkenes, alkynes, and allenes?
Chemistry (Weinheim an der Bergstrasse Germany), 2003Co-Authors: Dieter Lenoir, Cinzia ChiappeAbstract:The pi complexes first formed as essential intermediates from alkenes, alkynes, and allenes with bromine have been investigated in different solvents by UV-spectroscopy in combination with stopped-flow techniques allowing the determination of the equilibrium constants, K(f). Using alkenes with sterically protected double bonds, such as di-tert-butylstilbene and tetraneopentylethylene, the reaction stops at the stage of the 1:1 and 1:2 pi complex of the alkene with bromine as persistent species in 1,2-dichlorethane as solvent. Calculations by state-of-art ab initio and DFT methods reproduces the experimentally determined thermodynamic values quite well, and reveal the preferred structures and nature of both complexes for ethene, ethyne, and allene. Consideration of the entropy term reveals that complexes are stabilized in solution owing to reduction of the entropy loss by restricted translations and rotation. According to calculations these species are Mulliken-outer-type complexes with no or little charge transfer from bromine to the double or triple bond, respectively. The 1:2 complex has a close structural relationship to the Bromonium- or bromirenium ion, which is the subsequent intermediate on the reaction coordinate. Steric influences show a strong effect on the K(f) value, which can be explained by the polarizibility of the parent system. Addition-elimination often occurs. In bromination of adamantylidenadamantane and its derivatives the reaction stops at the stage of the Bromonium ion. The effect of various polar groups situated in equatorial homoallyl positions on the stability of corresponding pi complex and Bromonium ion has been studied in this series.
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Reactivity of homoallylic substituted adamantylideneadamantanes with bromine. Substituent effects on the stability of the ionic and nonionic intermediates.
The Journal of organic chemistry, 2002Co-Authors: Cinzia Chiappe, Antonietta De Rubertis, Ali Jaber, Dieter Lenoir, Carsten Wattenbach, Christian Silvio PomelliAbstract:Sterically congested adamantylideneadamantanes (1b−g) (X = Br, Cl, F, OH, OEt, OCOCH3), homoallylically substituted with equatorial groups (X), react with bromine in 1,2-dichloroethane to give a stable Bromonium ion intermediate or a substitution product depending on the nature of the substituent and on the bromine concentration. The nature of the substituent markedly affects the formation constant of the 1:1 π-complexes, as well as of the formation constant and reactivity of Bromonium ion intermediates. The different reactivity of the ionic intermediates, which depends on the nature of substituents, is attributed to Bromonium or bromocarbenium character of the intermediate, with the support of theoretical investigations. Ab initio calculations on 1:1 adamatylideneadamantane−Br2 complexes (2a−f) show that the substituent affects the stability of these species through electrostatic and dispersion effects. Solvent effects may also contribute to modulate the relative stability of these species.
Christopher D Braddock - One of the best experts on this subject based on the ideXlab platform.
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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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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.
Masahito Ochiai - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic Studies on the Generation and Properties of Superelectrophilic Singlet Carbenes from Bis(perfluoroalkanesulfonyl)Bromonium Ylides
The Journal of organic chemistry, 2016Co-Authors: Kazunori Miyamoto, Masahito Ochiai, Norihiro Tada, Susumu Iwasaki, Ryusuke Doi, Taiga Ota, Yufuko Kawano, Junpei Yamashita, Yuuta Sakai, Satoko HayashiAbstract:Pyrolysis of bis(perfluoroalkanesulfonyl)Bromonium ylides in various olefins results in highly stereospecific formation of cyclopropanes via unimolecular decomposition. Product analysis, kinetic study, substituent effects, and theoretical study revealed the generation of singlet bis(perfluoroalkanesulfonyl)carbenes stabilized by intramolecular coordination of sulfonyl oxygen.
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Mechanistic Studies on the Generation and Properties of Superelectrophilic Singlet Carbenes from Bis(perfluoroalkanesulfonyl)Bromonium Ylides
2016Co-Authors: Kazunori Miyamoto, Masahito Ochiai, Norihiro Tada, Susumu Iwasaki, Ryusuke Doi, Taiga Ota, Yufuko Kawano, Junpei Yamashita, Yuuta Sakai, Satoko HayashiAbstract:Pyrolysis of bis(perfluoroalkanesulfonyl)Bromonium ylides in various olefins results in highly stereospecific formation of cyclopropanes via unimolecular decomposition. Product analysis, kinetic study, substituent effects, and theoretical study revealed the generation of singlet bis(perfluoroalkanesulfonyl)carbenes stabilized by intramolecular coordination of sulfonyl oxygen
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Thermal and catalytic transylidations between halonium ylides and synthesis and reaction of stable aliphatic chloronium ylides
Journal of the American Chemical Society, 2008Co-Authors: Masahito Ochiai, Norihiro Tada, Takuya Okada, And Atushi Sota, Kazunori MiyamotoAbstract:Intermolecular transylidation between halonium ylides under thermal and catalytic (rhodium(II) acetate) conditions, which makes it possible to synthesize a hitherto unknown kind of aliphatic chloronium ylides as well as a variety of Bromonium and iodonium ylides, was developed. The uncatalyzed thermal transylidations of Bromonium to iodonium ylides probably involve generation of a reactive carbene :C(SO2CF3)2, being electrophilic in nature. Compared to the Bromonium and iodonium ylides, the chloronium ylide serves as a much better progenitor for generation of carbenes (or carbenoids) and efficiently undergoes cyclopropanation of olefins such as cyclooctadiene under uncatalyzed thermal conditions. A greater leaving group ability of the λ3-chloranyl and λ3-bromanyl groups compared to that of the λ3-iodanyl group seems to be responsible for the observed differences in reactivity between these halonium ylides.
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Synthesis and characterization of Bromonium ylides and their unusual ligand transfer reactions with N-heterocycles.
Journal of the American Chemical Society, 2006Co-Authors: Masahito Ochiai, Norihiro Tada, Kentaro Murai, Satoru Goto, Motoo ShiroAbstract:Stable aliphatic Bromonium ylides (RfSO2)2C-−Br+C6H4-p-CF3 (Rf = CF3, CF3(CF2)3) have been synthesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a ylide structure with an sp2 hybridization of the ylide carbanions and with little double-bond character for the ylidic bond. The Bromonium ylides selectively undergo transfer of the aryl group to nitrogen heterocycles, such as pyridines, yielding N-arylpyridinium salts. This is in a marked contrast to the reaction of the iodonium ylides, which produces pyridinium ylides through transylidations.
