- Practical and Selective sp3 C?H Bond Chlorination via Aminium Radicals
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The introduction of chlorine atoms into organic molecules is fundamental to the manufacture of industrial chemicals, the elaboration of advanced synthetic intermediates and also the fine-tuning of physicochemical and biological properties of drugs, agrochemicals and polymers. We report here a general and practical photochemical strategy enabling the site-selective chlorination of sp3 C?H bonds. This process exploits the ability of protonated N-chloroamines to serve as aminium radical precursors and also radical chlorinating agents. Upon photochemical initiation, an efficient radical-chain propagation is established allowing the functionalization of a broad range of substrates due to the large number of compatible functionalities. The ability to synergistically maximize both polar and steric effects in the H-atom transfer transition state through appropriate selection of the aminium radical has provided the highest known selectivity in radical sp3 C?H chlorination.
- McMillan, Alastair J.,Sieńkowska, Martyna,Di Lorenzo, Piero,Gransbury, Gemma K.,Chilton, Nicholas F.,Salamone, Michela,Ruffoni, Alessandro,Bietti, Massimo,Leonori, Daniele
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supporting information
p. 7132 - 7139
(2021/03/03)
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- Light-mediated deoxygenation of alcohols with a dimeric gold catalyst
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A new protocol for the reductive deoxygenation of primary alcohols was explored. This photo-mediated method combines a novel approach to bromination of alcohols merged with the powerful reducing capability of [Au2(dppm)2]Cl2 [dppm = 1,1-bis(diphenylphosphino)methane] as a photoredox catalyst. The highly efficient methods discussed are marked by the use of UVA light-emitting diodes, which have significantly reduced reaction times and lowered setup cost.
- McCallum, Terry,Slavko, Ekaterina,Morin, Mathieu,Barriault, Louis
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supporting information
p. 81 - 85
(2015/02/18)
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- Pheromone synthesis. Part 243: Synthesis and biological evaluation of (3R,13R,1′S)-1′-ethyl-2′-methylpropyl 3,13-dimethylpentadecanoate, the major component of the sex pheromone of Paulownia bagworm, Clania variegata, and its stereoisomers
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All of the four stereoisomers of (1′S)-1′-ethyl-2′-methylpropyl 3,13-dimethylpentadecanoate, the major component of the female sex pheromone of Clania variegata, were synthesized by employing olefin cross metathesis as the key reaction and starting from (R)- or (S)-2-methyl-1-butanol, (R)- or (S)-citronellal, and (S)-2-methyl-3-pentanol. Their bioassay revealed the (3R,13R,1′S)-isomer as the bioactive one, whose more efficient synthesis was achieved in two different ways by employing Wittig reaction as the key step.
- Mori, Kenji,Tashiro, Takuya,Zhao, Boguang,Suckling, David M.,El-Sayed, Ashraf M.
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experimental part
p. 2642 - 2653
(2010/05/18)
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- Formation, Stability, and Reactivity of Radical Cations of 1-Bromo-n-chloroalkanes in Aqueous Solution: A Pulse Radiolysis Study
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Hydroxyl radicals are able to form solute radical cations in acidic aqueous solutions of 1-bromo-n-chloroalkanes (n=1-6).Depending on the value of n, the bromine centered radical cation stabilizes on coordination with an unoxidized bromine atom from another molecule (intermolecular) or with an unoxidized chlorine atom of the same molecule (intramolecular).With n=2, 5, and 6, only dimer radical cations (λmax=430-450 nm) are formed through intermolecular coordination whereas, with n=1, 3, and 4, radical cations are stabilized both by intra- and intermolecular coordination, forming intramolecular radical cations (λmax=380 nm) or dimer radical cations (λmax=425-440 nm) at low and high solute concentrations, respectively.Cl2.- is unable to undergo an electron transfer reaction with 1-bromo-2-chloroethane whereas SO4.- is able to react with 1-bromo-2-chloroethane with a bimolecular rate constant of 8.3 * 106 dm3 mol-1 s-1.The dimer radical cation of 1-bromo-2-chloroethane is a strong one-electron oxidant and is able to undergo electron transfer reaction with a number of molecules with high rate constant values (109 dm3 mol-1 s-1).The dimer radical cation decays by a deprotonation mechanism, and the stability constant is determined to be 147 dm3 mol-1 at 25 deg C.Quantum chemical calculations of the strength of the three-electron bond between two heteroatoms at a semiempirical level with AMI parametrization show good correlation with experimental results.Good correlation, between experimantal results and theoretical calculations, is also observed for variation of the net atomic charge over bromine, the ionization potential (IP) of the molecule, and the difficulty of oxidation of various alkyl halides.
- Maity, D. K.,Mohan, H.,Chattopadhyay, S.,Mittal, J. P.
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p. 12195 - 12203
(2007/10/02)
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- The chain carriers of intermolecular hydrogen abstraction in the photobromination with N-bromosuccinimide; modifications of the chain carriers
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The photoinitiated bromination of 1-chloropentane with N-bromosuccinimide (NBS) in the presence of Br2 is compared with that of NBS and 1,1-dichloroethene to generate the succinimidyl radical (S radical) and with that of Br2 + K2CO3 to generate the bromine atom (Br radical) as the chain carriers.The relative reactivities of intermolecular H-abstraction (r-values) shown by the NBS + Br2 system decrease to levels lower than those shown by either S radical or Br radical chain propagations at lower temperatures under appropriate conditions: these observations indicate thepresence of a new chain propagating species that is assumed to be the bromine radical complex (BRC) modified from S radical or Br radical reversibly under the experimental conditions.Supporting evidence for the equilibria of S radical, Br radical, and BRC in the photodecomposition of NBS + Br2 is discussed.The unusual H-abstraction reactivity of Br radical toward the methyl hydrogens of 1-chloropentane was noted; this serves as independent support for the presence of a new radical propagation species.
- Zhang, Yu-Huang,Dong, Ming-Hua,Jiang, Xi-Kui,Chow, Yuan L.
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p. 1668 - 1675
(2007/10/02)
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- STEREOSPECIFIC SYNTHESIS OF PHEROMONES OF THE E-ALKENE SERIES FROM THE TELOMER OF BUTADIENE WITH PHENOL
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The stereospecific synthesis of 7E- and 9E-dodecenyl acetates, 7E- and 11E-tetradecenyl acetates, 11E-tetradecen-1-ol, and 11E-hexadecenyl acetate, i.e., E-olefinic sex pheromones, was realized from 1-phenoxy-2E,7-octadiene (the telomer of butadiene with phenol).
- Zakharkin, L. I.,Petrushkina, E. A.
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p. 1419 - 1422
(2007/10/02)
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