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William R Roush - One of the best experts on this subject based on the ideXlab platform.
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enantioselective syntheses of syn and anti β hydroxyallylsilanes via allene Hydroboration aldehyde allylboration reactions
Organic Letters, 2011Co-Authors: Ming Chen, William R RoushAbstract:The kinetic Hydroboration of allenylsilane 5 with (dIpc)2BH at −40 °C provides allylborane 9Z with ≥12:1 selectivity. When the Hydroboration is performed at temperatures above −40 °C, 9Z isomerizes to the thermodynamically more stable allylborane 9E with >20:1 selectivity. Subsequent treatment of 9Z or 9E with aldehydes at −78 °C provides syn- or anti-β-hydroxyallylsilanes, 7 or 8, respectively.
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thermodynamic control of 1 3 boratropic shifts of α and γ stannyl substituted allylboranes hyperconjugation outweighs steric effects
Organic Letters, 2011Co-Authors: Preston S Stewart, Ming Chen, William R Roush, Daniel H EssAbstract:(E)-δ-Stannyl homoallylic alcohols are prepared by an allene Hydroboration−aldehyde allylboration sequence (Chen, M.et al.J. Am. Chem. Soc. 2010, 132, 7881). Key to this reaction sequence is that the kinetic allene Hydroboration product, 2a, is less stable than and isomerizes to the more sterically congested α-stannylallylborane 3a (see abstract figure). An M06-2X density functional analysis shows that the C−Sn to boron σ−π hyperconjugation interaction is sufficiently stabilizing to override the steric congestion in 3a.
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enantioselective synthesis of 2 methyl 1 2 syn and 2 methyl 1 2 anti 3 butenediols via allene Hydroboration aldehyde allylboration reaction sequences
Journal of the American Chemical Society, 2009Co-Authors: Ming Chen, Masaki Handa, William R RoushAbstract:The Hydroboration of allene 7 with (dIpc)2BH at 0 °C provides the kinetic allylborane 12Z with >20:1 selectivity. However, when the Hydroboration is performed at 85 °C, the kinetically formed allylborane isomerizes to give the thermodynamic allylborane 12E with ≥12:1 selectivity. Subsequent treatment of 12Z or 12E with aldehydes at −78 °C, followed by oxidative workup, provides the 2-methyl-1,2-diols 8 and 9 in good yield and with 80−92% e.e.
Ming Chen - One of the best experts on this subject based on the ideXlab platform.
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enantioselective syntheses of syn and anti β hydroxyallylsilanes via allene Hydroboration aldehyde allylboration reactions
Organic Letters, 2011Co-Authors: Ming Chen, William R RoushAbstract:The kinetic Hydroboration of allenylsilane 5 with (dIpc)2BH at −40 °C provides allylborane 9Z with ≥12:1 selectivity. When the Hydroboration is performed at temperatures above −40 °C, 9Z isomerizes to the thermodynamically more stable allylborane 9E with >20:1 selectivity. Subsequent treatment of 9Z or 9E with aldehydes at −78 °C provides syn- or anti-β-hydroxyallylsilanes, 7 or 8, respectively.
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thermodynamic control of 1 3 boratropic shifts of α and γ stannyl substituted allylboranes hyperconjugation outweighs steric effects
Organic Letters, 2011Co-Authors: Preston S Stewart, Ming Chen, William R Roush, Daniel H EssAbstract:(E)-δ-Stannyl homoallylic alcohols are prepared by an allene Hydroboration−aldehyde allylboration sequence (Chen, M.et al.J. Am. Chem. Soc. 2010, 132, 7881). Key to this reaction sequence is that the kinetic allene Hydroboration product, 2a, is less stable than and isomerizes to the more sterically congested α-stannylallylborane 3a (see abstract figure). An M06-2X density functional analysis shows that the C−Sn to boron σ−π hyperconjugation interaction is sufficiently stabilizing to override the steric congestion in 3a.
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enantioselective synthesis of 2 methyl 1 2 syn and 2 methyl 1 2 anti 3 butenediols via allene Hydroboration aldehyde allylboration reaction sequences
Journal of the American Chemical Society, 2009Co-Authors: Ming Chen, Masaki Handa, William R RoushAbstract:The Hydroboration of allene 7 with (dIpc)2BH at 0 °C provides the kinetic allylborane 12Z with >20:1 selectivity. However, when the Hydroboration is performed at 85 °C, the kinetically formed allylborane isomerizes to give the thermodynamic allylborane 12E with ≥12:1 selectivity. Subsequent treatment of 12Z or 12E with aldehydes at −78 °C, followed by oxidative workup, provides the 2-methyl-1,2-diols 8 and 9 in good yield and with 80−92% e.e.
Rei Kinjo - One of the best experts on this subject based on the ideXlab platform.
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metal free regio and chemoselective Hydroboration of pyridines catalyzed by 1 3 2 diazaphosphenium triflate
Journal of the American Chemical Society, 2018Co-Authors: Bin Rao, Che Chang Chong, Rei KinjoAbstract:N-Heterocyclic phosphenium triflates (NHP-OTf) 1 serve as efficient catalysts for the regio- and chemoselective Hydroboration of pyridines under ambient condition with good functional group tolerance. Mechanistic studies indicate that a boronium salt, [(Py)2·Bpin]OTf 4, is generated concomitant with NHP-H 5 via hydride abstraction from HBpin by 1 in the initial reaction step. Hydride reduction of the activated pyridine in [(Py)2·Bpin]OTf 4 by NHP-H 5 affords the 1,4-Hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle.
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Metal-Free Regio- and Chemoselective Hydroboration of Pyridines Catalyzed by 1,3,2-Diazaphosphenium Triflate
2018Co-Authors: Bin Rao, Che Chang Chong, Rei KinjoAbstract:N-Heterocyclic phosphenium triflates (NHP-OTf) 1 serve as efficient catalysts for the regio- and chemoselective Hydroboration of pyridines under ambient condition with good functional group tolerance. Mechanistic studies indicate that a boronium salt, [(Py)2·Bpin]OTf 4, is generated concomitant with NHP-H 5 via hydride abstraction from HBpin by 1 in the initial reaction step. Hydride reduction of the activated pyridine in [(Py)2·Bpin]OTf 4 by NHP-H 5 affords the 1,4-Hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle
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catalytic Hydroboration of carbonyl derivatives imines and carbon dioxide
ChemInform, 2015Co-Authors: Che Chang Chong, Rei KinjoAbstract:Organoborane compounds present a class of versatile synthetic intermediate for myriad organic transformations. The direct addition of a B–H bond across unsaturated bond—namely, Hydroboration—is a powerful tool for the preparation of organoborane derivatives. This review outlines recent advances in catalytic Hydroboration of unsaturated organic compounds, specifically those involving C-X (X = N, O) bonds. We will discuss the chemical behavior of both transition metal catalysts and main group catalysts in Hydroboration. Emphasis will also be placed on the reaction mechanism of these catalytic reactions. Furthermore, recent achievements in catalytic Hydroboration of carbon dioxide CO2 will be highlighted.
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metal free σ bond metathesis in 1 3 2 diazaphospholene catalyzed Hydroboration of carbonyl compounds
ChemInform, 2015Co-Authors: Che Chang Chong, Hajime Hirao, Rei KinjoAbstract:The first metal-free catalytic Hydroboration of carbonyl derivatives is developed in which a catalytic amount of 1,3,2-diazaphospholene effectively promotes a Hydroboration reaction of aliphatic and aromatic aldehydes and ketones.
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metal free σ bond metathesis in 1 3 2 diazaphospholene catalyzed Hydroboration of carbonyl compounds
Angewandte Chemie, 2015Co-Authors: Che Chang Chong, Hajime Hirao, Rei KinjoAbstract:The first metal-free catalytic Hydroboration of carbonyl derivatives has been developed in which a catalytic amount of 1,3,2-diazaphospholene effectively promotes a Hydroboration reaction of aliphatic and aromatic aldehydes and ketones. The reaction mechanism involves the cleavage of both the PO bond of the alkoxyphosphine intermediate and the BH bond of pinacolborane as well as the formation of PH and BO bonds. Thus, the reaction proceeds through a non-metal σ-bond metathesis. Kinetic and computational studies suggest that the σ-bond metathesis occurred in a stepwise but nearly concerted manner.
Stephen P. Thomas - One of the best experts on this subject based on the ideXlab platform.
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kinetics and mechanism of the arase hoshi r2bh catalyzed alkyne Hydroboration alkenylboronate generation via b h c b metathesis
Journal of the American Chemical Society, 2019Co-Authors: Eduardo Nietosepulveda, Stephen P. Thomas, Andrew D Bage, Louise A Evans, Thomas Anthony Hunt, Andrew G Leach, Guy C LloydjonesAbstract:The mechanism of R2BH-catalyzed Hydroboration of alkynes by 1,3,2-dioxaborolanes has been investigated by in situ 19F NMR spectroscopy, kinetic simulation, isotope entrainment, single-turnover labeling (10B/2H), and density functional theory (DFT) calculations. For the Cy2BH-catalyzed Hydroboration 4-fluorophenylacetylene by pinacolborane, the resting state is the anti-Markovnikov addition product ArCH = CHBCy2. Irreversible and turnover-rate limiting reaction with pinacolborane (k ≈ 7 × 10–3 M–1 s–1) regenerates Cy2BH and releases E-Ar–CH═CHBpin. Two irreversible events proceed in concert with turnover. The first is a Markovnikov Hydroboration leading to regioisomeric Ar–C(Bpin)═CH2. This is unreactive to pinacolborane at ambient temperature, resulting in catalyst inhibition every ∼102 turnovers. The second is Hydroboration of the alkenylboronate to give ArCH2CH(BCy2)Bpin, again leading to catalyst inhibition. 9-BBN behaves analogously to Cy2BH, but with higher anti-Markovnikov selectivity, a lower barri...
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Earth-Abundant Metal Catalysis Enabled by Counterion Activation
2019Co-Authors: Riaz Agahi, Amy J. Challinor, Neil B. Carter, Stephen P. ThomasAbstract:A precatalyst activation strategy has been developed for earth-abundant metal catalysis enabled by counterion dissociation and demonstrated through alkene Hydroboration. Commercially available iron and cobalt tetrafluoroborate salts were found to catalyze the Hydroboration of aryl and alkyl alkenes with good functional group tolerance (Fe, 12 substrates; Co, 13 substrates) with three structurally distinct ligands. Key to this endogenous activation was counterion dissociation to generate fluoride which indirectly activates the precatalyst by reaction with pinacol borane
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Aluminum-Catalyzed Hydroboration of Alkenes
ACS Catalysis, 2018Co-Authors: Alessandro Bismuto, Michael J. Cowley, Stephen P. ThomasAbstract:The aluminum-catalyzed Hydroboration of alkenes with HBpin is reported using simple commercially available aluminum hydride precatalysts [LiAlH4 or sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al)]. Good substrate scope and functional group tolerance is demonstrated for alkene Hydroboration, and the protocol was also applied to the Hydroboration of ketone, ester, and nitrile functional groups, showing the potential for wider application. The aluminum-catalyzed Hydroboration is proposed to proceed by alkene hydroalumination, which generates an alkyl aluminum species that undergoes σ-bond metathesis with HBpin to drive turnover of the catalytic cycle.
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markovnikov selective activator free iron catalyzed vinylarene Hydroboration
ACS Catalysis, 2016Co-Authors: Alistair J Macnair, Clement R P Millet, Gary S Nichol, Alan Ironmonger, Stephen P. ThomasAbstract:Two series of structurally related alkoxy-tethered NHC iron(II) complexes have been developed as catalysts for the regioselective Hydroboration of alkenes. Significantly, Markonikov-selective alkene Hydroboration with HBpin has been controllably achieved using an iron catalyst (11 examples, 35–90% isolated yield) with up to 37:1 branched:linear selectivity. anti-Markovnikov-selective alkene Hydroboration was also achieved using HBcat and modification of the ligand backbone (6 examples, 44–71% yields). In both cases, ligand design has enabled activator-free low-oxidation-state iron catalysis.
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asymmetric Hydroboration of 1 1 disubstituted alkenes
ChemInform, 2009Co-Authors: Stephen P. Thomas, Varinder K AggarwalAbstract:A breakthrough in the asymmetric Hydroboration of notoriously difficult 1,1-disubstituted alkenes using a new family of highly effective Hydroboration reagents is described (see scheme). The intermediate boranes can be oxidized to alcohols or used in Suzuki–Miyaura cross-coupling reactions.
Juan M Lopezencarnacion - One of the best experts on this subject based on the ideXlab platform.
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supported single site ti iv on a metal organic framework for the Hydroboration of carbonyl compounds
Organometallics, 2017Co-Authors: Zhiyuan Huang, Dong Liu, Jeffrey Camachobunquin, Guanghui Zhang, Dali Yang, Juan M LopezencarnacionAbstract:A stable and structurally well-defined titanium alkoxide catalyst supported on a metal–organic-framework (MOF) of UiO-67 topology (ANL1-Ti(OiPr)2) was synthesized and fully characterized by a variety of analytical and spectroscopic techniques, including BET, TGA, PXRD, XAS, DRIFT, SEM, and DFT computations. The Ti-functionalized MOF was demonstrated active for the catalytic Hydroboration of a wide range of aldehydes and ketones with HBpin as the boron source. Compared to traditional homogeneous and supported Hydroboration catalysts, ANL1-Ti(OiPr)2 is completely recyclable and reusable, making it a promising Hydroboration catalyst alternative for green and sustainable chemical synthesis. In addition, ANL1-Ti(OiPr)2 catalyst exhibits remarkable Hydroboration selectivity toward aldehydes vs ketone in competitive study. DFT calculations suggest that the catalytic Hydroboration proceeds via a (1) hydride transfer between the active Ti-hydride species and a carbonyl moiety (rate-determining step) and (2) alkoxi...
