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Paul E Floreancig - One of the best experts on this subject based on the ideXlab platform.
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stereoselective piperidine synthesis through oxidative carbon hydrogen Bond functionalizations of enamides
ChemInform, 2012Co-Authors: Gediminas J Brizgys, Hyung Hoon Jung, Paul E FloreancigAbstract:In the presence of DBU, N-vinyl carbamates, sulfonamides, and amides that contain pendent π-nucleophiles such as allylsilane, enolsilane, propargylsilane, and enol acetate, give the piperidines within minutes.
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synthesis of sulfur containing heterocycles through oxidative carbon hydrogen Bond functionalization
Organic Letters, 2012Co-Authors: Yubo Cui, Paul E FloreancigAbstract:Vinyl sulfides react rapidly and efficiently with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form α,β-unsaturated thiocarbenium ions through oxidative carbon–hydrogen Bond cleavage. These electrophiles couple with appended π-nucleophiles to yield sulfur-containing heterocycles through carbon–carbon Bond formation. Several nucleophiles are compatible with the procedure, and the reactions generally proceed through readily predictable transition states.
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stereoselective piperidine synthesis through oxidative carbon hydrogen Bond functionalizations of enamides
Chemical Science, 2012Co-Authors: Gediminas J Brizgys, Hyung Hoon Jung, Paul E FloreancigAbstract:N-Vinyl amides, carbamates, and sulfonamides that contain pendent π-nucleophiles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form piperidine structures with good to excellent levels of efficiency and stereocontrol. Reactions proceed nearly instantaneously at room temperature. Transition state models show the preferred configuration around the intermediate acyliminium ion and the orientation of the nucleophile.
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Aromatic Cations from Oxidative Carbon–Hydrogen Bond Cleavage in Bimolecular Carbon–Carbon Bond Forming Reactions
2012Co-Authors: Dane J. Clausen, Paul E FloreancigAbstract:Chromenes and isochromenes react quickly with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form persistent aromatic oxocarbenium ions through oxidative carbon–hydrogen cleavage. This process is tolerant of electron-donating and electron-withdrawing groups on the benzene ring and additional substitution on the pyran ring. A variety of nucleophiles can be added to these cations to generate a diverse set of structures
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diversity oriented synthesis of a library of substituted tetrahydropyrones using oxidative carbon hydrogen Bond activation and click chemistry
Molecules, 2011Co-Authors: Nilesh Zaware, Matthew G Laporte, Ramy Farid, Lei Liu, Peter Wipf, Paul E FloreancigAbstract:Eighteen (2RS,6RS)-2-(4-methoxyphenyl)-6-(substituted ethyl)dihydro-2H-pyran-4(3H)ones were synthesized via a DDQ-mediated oxidative Carbon-Hydrogen Bond activation reaction. Fourteen of these tetrahydropyrans were substituted with triazoles readily assembled via azide-alkyne click-chemistry reactions. Examples of a linked benzotriazole and pyrazole motif were also prepared. To complement the structural diversity, the alcohol substrates were obtained from stereoselective reductions of the tetrahydropyrone. This library provides rapid access to structurally diverse non-natural compounds to be screened against a variety of biological targets.
Michael B Hall - One of the best experts on this subject based on the ideXlab platform.
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probing the carbon hydrogen activation of alkanes following photolysis of tp rh cnr carbodiimide a computational and time resolved infrared spectroscopic study
Journal of the American Chemical Society, 2017Co-Authors: Jia Guan, Michael B Hall, Alisdair Wriglesworth, Xuezhong Sun, Snežana D Zaric, Meagan E. Evans, William D. Jones, Michael Towrie, Michael W GeorgeAbstract:Carbon–hydrogen Bond activation of alkanes by Tp′Rh(CNR) (Tp′ = Tp = trispyrazolylborate or Tp* = tris(3,5-dimethylpyrazolyl)borate) were followed by time-resolved infrared spectroscopy (TRIR) in the υ(CNR) and υ(B−H) spectral regions on Tp*Rh(CNCH2CMe3), and their reaction mechanisms were modeled by density functional theory (DFT) on TpRh(CNMe). The major intermediate species were: κ3-η1-alkane complex (1); κ2-η2-alkane complex (2); and κ3-alkyl hydride (3). Calculations predict that the barrier between 1 and 2 arises from a triplet-singlet crossing and intermediate 2 proceeds over the rate-determining C–H activation barrier to give the final product 3. The activation lifetimes measured for the Tp*Rh(CNR) and Tp*Rh(CO) fragments with n-heptane and four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) increase with alkanes size and show a dramatic increase between C6H12 and C7H14. A similar step-like behavior was observed previously with CpRh(CO) and Cp*Rh(CO) fragments and is attributed to the wider differe...
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Probing the Carbon–Hydrogen Activation of Alkanes Following Photolysis of Tp′Rh(CNR)(carbodiimide): A Computational and Time-Resolved Infrared Spectroscopic Study
2017Co-Authors: Jia Guan, Michael B Hall, Alisdair Wriglesworth, Xuezhong Sun, Edward N. Brothers, Snežana D. Zarić, Meagan E. Evans, William D. Jones, Michael Towrie, Michael W GeorgeAbstract:Carbon–hydrogen Bond activation of alkanes by Tp′Rh(CNR) (Tp′ = Tp = trispyrazolylborate or Tp* = tris(3,5-dimethylpyrazolyl)borate) were followed by time-resolved infrared spectroscopy (TRIR) in the υ(CNR) and υ(B−H) spectral regions on Tp*Rh(CNCH2CMe3), and their reaction mechanisms were modeled by density functional theory (DFT) on TpRh(CNMe). The major intermediate species were: κ3-η1-alkane complex (1); κ2-η2-alkane complex (2); and κ3-alkyl hydride (3). Calculations predict that the barrier between 1 and 2 arises from a triplet-singlet crossing and intermediate 2 proceeds over the rate-determining C–H activation barrier to give the final product 3. The activation lifetimes measured for the Tp*Rh(CNR) and Tp*Rh(CO) fragments with n-heptane and four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) increase with alkanes size and show a dramatic increase between C6H12 and C7H14. A similar step-like behavior was observed previously with CpRh(CO) and Cp*Rh(CO) fragments and is attributed to the wider difference in C–H Bonds that appear at C7H14. However, Tp′Rh(CNR) and Tp′Rh(CO) fragments have much longer absolute lifetimes compared to those of CpRh(CO) and Cp*Rh(CO) fragments, because the reduced electron density in dechelated κ2-η2-alkane Tp′ complexes stabilizes the d8 Rh(I) in a square-planar geometry and weakens the metal′s ability for oxidative addition of the C–H Bond. Further, the Tp′Rh(CNR) fragment has significantly slower rates of C–H activation in comparison to the Tp′Rh(CO) fragment for the larger cycloalkanes, because the steric bulk of the neopentyl isocyanide ligand hinders the rechelation in κ2-Tp′Rh(CNR)(cycloalkane) species and results in the C–H activation without the assistance of the rechelation
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carbon hydrogen Bond activation in bis 2 6 dimethylbenzenethiolato tris trimethylphosphine ruthenium ii ligand dances and solvent transformations
Organometallics, 2015Co-Authors: Amanda L Pitts, Michael B HallAbstract:Density functional theory (DFT) calculations are used to predict the mechanism for the intramolecular carbon–hydrogen Bond activation of an ortho methyl group on the RuII(SC6H3Me2-2,6-κ1S)2(PMe3)3 complex to form the cycloruthenated product cis-Ru[SC6H3-(2-CH2)(6-Me)-κ2S2C](PMe3)4 and HSC6H3Me2-2,6 in the presence of PMe3. The DFT calculations also show how changing the solvent from benzene to methanol prevents C–H activation and results in the unactivated six-coordinate product Ru(SC6H3Me2-2,6-κ1S)2(PMe3)4 in 100% yield. The reactant was determined to have two plausible σ-Bond metathesis pathways in which to react, one for each of the two thiolate ligands. The steps in both mechanisms were influenced by the electronic interactions between the sulfur lone pairs and the Ru 4d orbitals and the steric repulsion between the methyl groups on the five ligands in such a way that the methyl group in the SAr (Ar = SC6H3Me2-2,6) ligand closest to the Ru pirouettes away to activate the other methyl group. The equato...
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carbon hydrogen activation of cycloalkanes by cyclopentadienylcarbonylrhodium a lifetime enigma
Journal of the American Chemical Society, 2014Co-Authors: Amanda L Pitts, Alisdair Wriglesworth, Xuezhong Sun, James A Calladine, Snežana D Zaric, Michael W George, Michael B HallAbstract:Carbon–hydrogen Bond activation reactions of four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) by the Cp′Rh(CO) fragments (Cp′ = η5-C5H5 (Cp) or η5-C5Me5 (Cp*)) were modeled theoretically by combining density functional and coupled cluster theories, and their reaction rates were measured by fast time-resolved infrared spectroscopy. The reaction has two steps, starting with the formation of a σ-complex intermediate, followed by oxidative addition of the C–H Bond by the rhodium. A range of σ-complex stabilities among the electronically unique C–H Bonds in a cycloalkane were calculated and are related to the individual strengths of the C–H Bond’s interactions with the Rh fragment and the steric repulsion that is incurred upon forming the specific σ-complex. The unexpectedly large increase in the lifetimes of the σ-complexes from cyclohexane to cycloheptane was predicted to be due to the large range of stabilities of the different σ-complexes found for cycloheptane. The reaction lifetimes were simulated with...
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theoretical studies of inorganic and organometallic reaction mechanisms 9 intermolecular versus intramolecular carbon hydrogen Bond activation in zirconium rhodium and iridium complexes
Organometallics, 1996Co-Authors: Rogelio Jimenezcatano, Michael B HallAbstract:Ab initio quantum mechanical calculations were performed on model reactions to analyze the behavior of intermolecular versus intramolecular C−H Bond activation in zirconium, rhodium, and iridium co...
Olga García Mancheño - One of the best experts on this subject based on the ideXlab platform.
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Mild Radical Oxidative sp3-Carbon–Hydrogen Functionalization: Innovative Construction of Isoxazoline and Dibenz[b,f]oxepine/azepine Derivatives
Synlett, 2016Co-Authors: Andrea Gini, Olga García MancheñoAbstract:Direct carbon–hydrogen Bond functionalization has emerged as a powerful synthetic method for the straightforward and modular functionalization of organic molecules. In this account, we described our latest contributions in the area of oxidative sp3-carbon–hydrogen Bond functionalization using mild radical oxidants for the construction of structurally important heterocycles. We have developed two new methodologies in which a new class of substrate and an uncommon nucleophilic reagent have been introduced to the existing palette of reaction partners for oxidative carbon–hydrogen functionalization. To achieve these results, the 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) radical and a benzoyl peroxide/copper(I) system have been employed as oxidants for the dehydrogenative one-pot synthesis of N-alkoxycarbonyl-protected isoxazolines from hydroxylamines and for the synthesis of dibenz[b,f]oxepines, dibenzo[b,f]thiepines, and dibenz[b,f]azepines from simple xanthenes, thioxanthenes, and acridanes, respectively. 1 Introduction 2 2,2,6,6-Tetramethylpiperidinyloxyl-Mediated Dehydrogenative Formation and Trapping of Unstable Nitrones: Synthesis of N-Alkoxycarbonyl-Protected Isoxazoline Derivatives 3 Oxidative sp3-Carbon–Hydrogen Bond Functionalization and Ring Expansion with Trimethylsilyldiazomethane: Synthesis of Dibenzoxepines, Dibenzothiepines, and Dibenzazepines 4 Conclusions and Outlook
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mild radical oxidative sp3 carbon hydrogen functionalization innovative construction of isoxazoline and dibenz b f oxepine azepine derivatives
Synlett, 2016Co-Authors: Andrea Gini, Olga García MancheñoAbstract:Direct carbon–hydrogen Bond functionalization has emerged as a powerful synthetic method for the straightforward and modular functionalization of organic molecules. In this account, we described our latest contributions in the area of oxidative sp3-carbon–hydrogen Bond functionalization using mild radical oxidants for the construction of structurally important heterocycles. We have developed two new methodologies in which a new class of substrate and an uncommon nucleophilic reagent have been introduced to the existing palette of reaction partners for oxidative carbon–hydrogen functionalization. To achieve these results, the 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) radical and a benzoyl peroxide/copper(I) system have been employed as oxidants for the dehydrogenative one-pot synthesis of N-alkoxycarbonyl-protected isoxazolines from hydroxylamines and for the synthesis of dibenz[b,f]oxepines, dibenzo[b,f]thiepines, and dibenz[b,f]azepines from simple xanthenes, thioxanthenes, and acridanes, respectively. 1 Introduction 2 2,2,6,6-Tetramethylpiperidinyloxyl-Mediated Dehydrogenative Formation and Trapping of Unstable Nitrones: Synthesis of N-Alkoxycarbonyl-Protected Isoxazoline Derivatives 3 Oxidative sp3-Carbon–Hydrogen Bond Functionalization and Ring Expansion with Trimethylsilyldiazomethane: Synthesis of Dibenzoxepines, Dibenzothiepines, and Dibenzazepines 4 Conclusions and Outlook
Michael W George - One of the best experts on this subject based on the ideXlab platform.
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probing the carbon hydrogen activation of alkanes following photolysis of tp rh cnr carbodiimide a computational and time resolved infrared spectroscopic study
Journal of the American Chemical Society, 2017Co-Authors: Jia Guan, Michael B Hall, Alisdair Wriglesworth, Xuezhong Sun, Snežana D Zaric, Meagan E. Evans, William D. Jones, Michael Towrie, Michael W GeorgeAbstract:Carbon–hydrogen Bond activation of alkanes by Tp′Rh(CNR) (Tp′ = Tp = trispyrazolylborate or Tp* = tris(3,5-dimethylpyrazolyl)borate) were followed by time-resolved infrared spectroscopy (TRIR) in the υ(CNR) and υ(B−H) spectral regions on Tp*Rh(CNCH2CMe3), and their reaction mechanisms were modeled by density functional theory (DFT) on TpRh(CNMe). The major intermediate species were: κ3-η1-alkane complex (1); κ2-η2-alkane complex (2); and κ3-alkyl hydride (3). Calculations predict that the barrier between 1 and 2 arises from a triplet-singlet crossing and intermediate 2 proceeds over the rate-determining C–H activation barrier to give the final product 3. The activation lifetimes measured for the Tp*Rh(CNR) and Tp*Rh(CO) fragments with n-heptane and four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) increase with alkanes size and show a dramatic increase between C6H12 and C7H14. A similar step-like behavior was observed previously with CpRh(CO) and Cp*Rh(CO) fragments and is attributed to the wider differe...
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Probing the Carbon–Hydrogen Activation of Alkanes Following Photolysis of Tp′Rh(CNR)(carbodiimide): A Computational and Time-Resolved Infrared Spectroscopic Study
2017Co-Authors: Jia Guan, Michael B Hall, Alisdair Wriglesworth, Xuezhong Sun, Edward N. Brothers, Snežana D. Zarić, Meagan E. Evans, William D. Jones, Michael Towrie, Michael W GeorgeAbstract:Carbon–hydrogen Bond activation of alkanes by Tp′Rh(CNR) (Tp′ = Tp = trispyrazolylborate or Tp* = tris(3,5-dimethylpyrazolyl)borate) were followed by time-resolved infrared spectroscopy (TRIR) in the υ(CNR) and υ(B−H) spectral regions on Tp*Rh(CNCH2CMe3), and their reaction mechanisms were modeled by density functional theory (DFT) on TpRh(CNMe). The major intermediate species were: κ3-η1-alkane complex (1); κ2-η2-alkane complex (2); and κ3-alkyl hydride (3). Calculations predict that the barrier between 1 and 2 arises from a triplet-singlet crossing and intermediate 2 proceeds over the rate-determining C–H activation barrier to give the final product 3. The activation lifetimes measured for the Tp*Rh(CNR) and Tp*Rh(CO) fragments with n-heptane and four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) increase with alkanes size and show a dramatic increase between C6H12 and C7H14. A similar step-like behavior was observed previously with CpRh(CO) and Cp*Rh(CO) fragments and is attributed to the wider difference in C–H Bonds that appear at C7H14. However, Tp′Rh(CNR) and Tp′Rh(CO) fragments have much longer absolute lifetimes compared to those of CpRh(CO) and Cp*Rh(CO) fragments, because the reduced electron density in dechelated κ2-η2-alkane Tp′ complexes stabilizes the d8 Rh(I) in a square-planar geometry and weakens the metal′s ability for oxidative addition of the C–H Bond. Further, the Tp′Rh(CNR) fragment has significantly slower rates of C–H activation in comparison to the Tp′Rh(CO) fragment for the larger cycloalkanes, because the steric bulk of the neopentyl isocyanide ligand hinders the rechelation in κ2-Tp′Rh(CNR)(cycloalkane) species and results in the C–H activation without the assistance of the rechelation
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carbon hydrogen activation of cycloalkanes by cyclopentadienylcarbonylrhodium a lifetime enigma
Journal of the American Chemical Society, 2014Co-Authors: Amanda L Pitts, Alisdair Wriglesworth, Xuezhong Sun, James A Calladine, Snežana D Zaric, Michael W George, Michael B HallAbstract:Carbon–hydrogen Bond activation reactions of four cycloalkanes (C5H10, C6H12, C7H14, and C8H16) by the Cp′Rh(CO) fragments (Cp′ = η5-C5H5 (Cp) or η5-C5Me5 (Cp*)) were modeled theoretically by combining density functional and coupled cluster theories, and their reaction rates were measured by fast time-resolved infrared spectroscopy. The reaction has two steps, starting with the formation of a σ-complex intermediate, followed by oxidative addition of the C–H Bond by the rhodium. A range of σ-complex stabilities among the electronically unique C–H Bonds in a cycloalkane were calculated and are related to the individual strengths of the C–H Bond’s interactions with the Rh fragment and the steric repulsion that is incurred upon forming the specific σ-complex. The unexpectedly large increase in the lifetimes of the σ-complexes from cyclohexane to cycloheptane was predicted to be due to the large range of stabilities of the different σ-complexes found for cycloheptane. The reaction lifetimes were simulated with...
Andrea Gini - One of the best experts on this subject based on the ideXlab platform.
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Mild Radical Oxidative sp3-Carbon–Hydrogen Functionalization: Innovative Construction of Isoxazoline and Dibenz[b,f]oxepine/azepine Derivatives
Synlett, 2016Co-Authors: Andrea Gini, Olga García MancheñoAbstract:Direct carbon–hydrogen Bond functionalization has emerged as a powerful synthetic method for the straightforward and modular functionalization of organic molecules. In this account, we described our latest contributions in the area of oxidative sp3-carbon–hydrogen Bond functionalization using mild radical oxidants for the construction of structurally important heterocycles. We have developed two new methodologies in which a new class of substrate and an uncommon nucleophilic reagent have been introduced to the existing palette of reaction partners for oxidative carbon–hydrogen functionalization. To achieve these results, the 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) radical and a benzoyl peroxide/copper(I) system have been employed as oxidants for the dehydrogenative one-pot synthesis of N-alkoxycarbonyl-protected isoxazolines from hydroxylamines and for the synthesis of dibenz[b,f]oxepines, dibenzo[b,f]thiepines, and dibenz[b,f]azepines from simple xanthenes, thioxanthenes, and acridanes, respectively. 1 Introduction 2 2,2,6,6-Tetramethylpiperidinyloxyl-Mediated Dehydrogenative Formation and Trapping of Unstable Nitrones: Synthesis of N-Alkoxycarbonyl-Protected Isoxazoline Derivatives 3 Oxidative sp3-Carbon–Hydrogen Bond Functionalization and Ring Expansion with Trimethylsilyldiazomethane: Synthesis of Dibenzoxepines, Dibenzothiepines, and Dibenzazepines 4 Conclusions and Outlook
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mild radical oxidative sp3 carbon hydrogen functionalization innovative construction of isoxazoline and dibenz b f oxepine azepine derivatives
Synlett, 2016Co-Authors: Andrea Gini, Olga García MancheñoAbstract:Direct carbon–hydrogen Bond functionalization has emerged as a powerful synthetic method for the straightforward and modular functionalization of organic molecules. In this account, we described our latest contributions in the area of oxidative sp3-carbon–hydrogen Bond functionalization using mild radical oxidants for the construction of structurally important heterocycles. We have developed two new methodologies in which a new class of substrate and an uncommon nucleophilic reagent have been introduced to the existing palette of reaction partners for oxidative carbon–hydrogen functionalization. To achieve these results, the 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) radical and a benzoyl peroxide/copper(I) system have been employed as oxidants for the dehydrogenative one-pot synthesis of N-alkoxycarbonyl-protected isoxazolines from hydroxylamines and for the synthesis of dibenz[b,f]oxepines, dibenzo[b,f]thiepines, and dibenz[b,f]azepines from simple xanthenes, thioxanthenes, and acridanes, respectively. 1 Introduction 2 2,2,6,6-Tetramethylpiperidinyloxyl-Mediated Dehydrogenative Formation and Trapping of Unstable Nitrones: Synthesis of N-Alkoxycarbonyl-Protected Isoxazoline Derivatives 3 Oxidative sp3-Carbon–Hydrogen Bond Functionalization and Ring Expansion with Trimethylsilyldiazomethane: Synthesis of Dibenzoxepines, Dibenzothiepines, and Dibenzazepines 4 Conclusions and Outlook