The Experts below are selected from a list of 576 Experts worldwide ranked by ideXlab platform
Matthew S Sigman - One of the best experts on this subject based on the ideXlab platform.
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relative reactivity of Alkenyl Alcohols in the palladium catalyzed redox relay heck reaction
2015Co-Authors: Margaret J Hilton, Bin Cheng, Benjamin R Buckley, Olaf Wiest, Matthew S SigmanAbstract:The relative rates of Alkenyl Alcohols in the Pd-catalyzed redox-relay Heck reaction were measured in order to examine the effect of their steric and electronic properties on the rate-determining step. Competition experiments between an allylic Alkenyl Alcohol and two substrates with differing chain lengths revealed that the allylic Alcohol reacts 3-4 times faster in either case. Competition between di- and trisubstituted Alkenyl Alcohols provided an interesting scenario, in which the disubstituted alkene was consumed first followed by reaction of the trisubstituted alkene. Consistent with this observation, the transition structures for the migratory insertion of the aryl group into the di- and trisubstituted alkenes were calculated with a lower barrier for the former. An internal competition between a substrate containing two Alcohols with differing chain lengths demonstrated the catalyst's preference for migrating towards the closest Alcohol. Additionally, it was observed that increasing the electron density in the arene boronic acid promotes a faster reaction, which correlates with Hammett σp values to give a ρ of -0.87.
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enantioselective redox relay oxidative heck arylations of acyclic Alkenyl Alcohols using boronic acids
2013Co-Authors: Tiansheng Mei, Erik W Werner, Alexander J Burckle, Matthew S SigmanAbstract:A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the Alkenyl Alcohol.
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Enantioselective Redox-Relay Oxidative Heck Arylations of Acyclic Alkenyl Alcohols using Boronic Acids
2013Co-Authors: Tiansheng Mei, Erik W Werner, Alexander J Burckle, Matthew S SigmanAbstract:A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the Alkenyl Alcohol
Xiaotai Wang - One of the best experts on this subject based on the ideXlab platform.
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a computational mechanistic study of an unprecedented heck type relay reaction insight into the origins of regio and enantioselectivities
2014Co-Authors: Yanfeng Dang, Shuanglin Qu, Zhi Xiang Wang, Xiaotai WangAbstract:Density functional theory (DFT) calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or Alkenyl Alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand. The reaction not only controls the regio- and enantioselectivities of arylation of the C═C bond, but also forms the carbonyl functionality up to four bonds away from the aryl substituent via tandem C═C bond migration and enol-to-keto conversion. Computations performed on representative reaction systems allow us to propose a detailed mechanism with several key steps. Initial oxidation of palladium(0) by aryldiazonium generates active arylpalladium(II) species that bind the C═C bond of an allylic or Alkenyl Alcohol. The activated C═C bond inserts into the palladium–aryl moiety to attain aryl substitution and a chiral carbon center, and the resulting complex undergoes β-hydride elimination to give a new C═C bond that can repeat the ins...
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A Computational Mechanistic Study of an Unprecedented Heck-Type Relay Reaction: Insight into the Origins of Regio- and Enantioselectivities
2014Co-Authors: Yanfeng Dang, Zhi Xiang Wang, Xiaotai WangAbstract:Density functional theory (DFT) calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or Alkenyl Alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand. The reaction not only controls the regio- and enantioselectivities of arylation of the CC bond, but also forms the carbonyl functionality up to four bonds away from the aryl substituent via tandem CC bond migration and enol-to-keto conversion. Computations performed on representative reaction systems allow us to propose a detailed mechanism with several key steps. Initial oxidation of palladium(0) by aryldiazonium generates active arylpalladium(II) species that bind the CC bond of an allylic or Alkenyl Alcohol. The activated CC bond inserts into the palladium–aryl moiety to attain aryl substitution and a chiral carbon center, and the resulting complex undergoes β-hydride elimination to give a new CC bond that can repeat the insertion/elimination process to move down the carbon chain to form an enol that tautomerizes to a highly stable carbonyl final product. The calculations reveal that the CC bond migratory insertion step determines both the regioselectivity and the enantioselectivity of arylation, with the former arising mainly from the electronic effect of the hydroxyl group on the charge distribution over the CC bond and the latter originating from a combination of steric repulsion, trans influence, and C–H/π dispersion interactions
Tiansheng Mei - One of the best experts on this subject based on the ideXlab platform.
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enantioselective redox relay oxidative heck arylations of acyclic Alkenyl Alcohols using boronic acids
2013Co-Authors: Tiansheng Mei, Erik W Werner, Alexander J Burckle, Matthew S SigmanAbstract:A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the Alkenyl Alcohol.
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Enantioselective Redox-Relay Oxidative Heck Arylations of Acyclic Alkenyl Alcohols using Boronic Acids
2013Co-Authors: Tiansheng Mei, Erik W Werner, Alexander J Burckle, Matthew S SigmanAbstract:A general, highly selective asymmetric redox-relay oxidative Heck reaction using achiral or racemic acyclic alkenols and boronic acid derivatives is reported. This reaction delivers remotely functionalized arylated carbonyl products from acyclic alkenol substrates, with excellent enantioselectivity under mild conditions, bearing a range of useful functionality. A preliminary mechanistic investigation suggests that the regioselectivity of the initial migratory insertion is highly dependent on the electronic nature of the boronic acid and more subtle electronic effects of the Alkenyl Alcohol
Yui Satoh - One of the best experts on this subject based on the ideXlab platform.
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catalytic synthesis of saturated oxygen heterocycles by hydrofunctionalization of unactivated olefins unprotected and protected strategies
2016Co-Authors: Hiroki Shigehisa, Miki Hayashi, Haruna Ohkawa, Tsuyoshi Suzuki, Hiroki Okayasu, Mayumi Mukai, Ayaka Yamazaki, Ryohei Kawai, Harue Kikuchi, Yui SatohAbstract:A mild, general, and functional group tolerant intramolecular hydroalkoxylation and hydroacyloxylation of unactivated olefins using a Co(salen) complex, an N-fluoropyridinium salt, and a disiloxane reagent is described. This reaction was carried out at room temperature and afforded five- and six-membered oxygen heterocyclic compounds, such as cyclic ethers and lactones. The Co complex was optimized for previously rare medium ring formation by hydrofunctionalization of unactivated olefins. The powerful Co catalyst system also enables the deprotective hydroalkoxylation of O-protected Alkenyl Alcohol and hydroacyloxylation of Alkenyl ester to afford cyclic ethers and lactones directly. The substrate scope and mechanistic proof of deprotection were investigated. The experimental evidence supports the concerted transition state of the bond-forming step involving a cationic Co complex.
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Catalytic Synthesis of Saturated Oxygen Heterocycles by Hydrofunctionalization of Unactivated Olefins: Unprotected and Protected Strategies
2016Co-Authors: Hiroki Shigehisa, Miki Hayashi, Haruna Ohkawa, Tsuyoshi Suzuki, Hiroki Okayasu, Mayumi Mukai, Ayaka Yamazaki, Ryohei Kawai, Harue Kikuchi, Yui SatohAbstract:A mild, general, and functional group tolerant intramolecular hydroalkoxylation and hydroacyloxylation of unactivated olefins using a Co(salen) complex, an N-fluoropyridinium salt, and a disiloxane reagent is described. This reaction was carried out at room temperature and afforded five- and six-membered oxygen heterocyclic compounds, such as cyclic ethers and lactones. The Co complex was optimized for previously rare medium ring formation by hydrofunctionalization of unactivated olefins. The powerful Co catalyst system also enables the deprotective hydroalkoxylation of O-protected Alkenyl Alcohol and hydroacyloxylation of Alkenyl ester to afford cyclic ethers and lactones directly. The substrate scope and mechanistic proof of deprotection were investigated. The experimental evidence supports the concerted transition state of the bond-forming step involving a cationic Co complex
Yanfeng Dang - One of the best experts on this subject based on the ideXlab platform.
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a computational mechanistic study of an unprecedented heck type relay reaction insight into the origins of regio and enantioselectivities
2014Co-Authors: Yanfeng Dang, Shuanglin Qu, Zhi Xiang Wang, Xiaotai WangAbstract:Density functional theory (DFT) calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or Alkenyl Alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand. The reaction not only controls the regio- and enantioselectivities of arylation of the C═C bond, but also forms the carbonyl functionality up to four bonds away from the aryl substituent via tandem C═C bond migration and enol-to-keto conversion. Computations performed on representative reaction systems allow us to propose a detailed mechanism with several key steps. Initial oxidation of palladium(0) by aryldiazonium generates active arylpalladium(II) species that bind the C═C bond of an allylic or Alkenyl Alcohol. The activated C═C bond inserts into the palladium–aryl moiety to attain aryl substitution and a chiral carbon center, and the resulting complex undergoes β-hydride elimination to give a new C═C bond that can repeat the ins...
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A Computational Mechanistic Study of an Unprecedented Heck-Type Relay Reaction: Insight into the Origins of Regio- and Enantioselectivities
2014Co-Authors: Yanfeng Dang, Zhi Xiang Wang, Xiaotai WangAbstract:Density functional theory (DFT) calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or Alkenyl Alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand. The reaction not only controls the regio- and enantioselectivities of arylation of the CC bond, but also forms the carbonyl functionality up to four bonds away from the aryl substituent via tandem CC bond migration and enol-to-keto conversion. Computations performed on representative reaction systems allow us to propose a detailed mechanism with several key steps. Initial oxidation of palladium(0) by aryldiazonium generates active arylpalladium(II) species that bind the CC bond of an allylic or Alkenyl Alcohol. The activated CC bond inserts into the palladium–aryl moiety to attain aryl substitution and a chiral carbon center, and the resulting complex undergoes β-hydride elimination to give a new CC bond that can repeat the insertion/elimination process to move down the carbon chain to form an enol that tautomerizes to a highly stable carbonyl final product. The calculations reveal that the CC bond migratory insertion step determines both the regioselectivity and the enantioselectivity of arylation, with the former arising mainly from the electronic effect of the hydroxyl group on the charge distribution over the CC bond and the latter originating from a combination of steric repulsion, trans influence, and C–H/π dispersion interactions