- Manganese catalyzed asymmetric transfer hydrogenation of ketones
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The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral PxNy-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)5] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP2N4 (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee.
- Zhang, Guang-Ya,Ruan, Sun-Hong,Li, Yan-Yun,Gao, Jing-Xing
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supporting information
p. 1415 - 1418
(2020/11/20)
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- Discovery of florylpicoxamid, a mimic of a macrocyclic natural product
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Natural products have routinely been used both as sources of and inspiration for new crop protection active ingredients. The natural product UK-2A has potent anti-fungal activity but lacks key attributes for field translation. Post-fermentation conversion of UK-2A to fenpicoxamid resulted in an active ingredient with a new target site of action for cereal and banana pathogens. Here we demonstrate the creation of a synthetic variant of fenpicoxamid via identification of the structural elements of UK-2A that are needed for anti-fungal activity. Florylpicoxamid is a non-macrocyclic active ingredient bearing two fewer stereocenters than fenpicoxamid, controls a broad spectrum of fungal diseases at low use rates and has a concise, scalable route which is aligned with green chemistry principles. The development of florylpicoxamid represents the first example of using a stepwise deconstruction of a macrocyclic natural product to design a fully synthetic crop protection active ingredient.
- Meyer, Kevin G.,Bravo-Altamirano, Karla,Herrick, Jessica,Loy, Brian A.,Yao, Chenglin,Nugent, Ben,Buchan, Zachary,Daeuble, John F.,Heemstra, Ron,Jones, David M.,Wilmot, Jeremy,Lu, Yu,DeKorver, Kyle,DeLorbe, Johnathan,Rigoli, Jared
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- Borohydride intermediates pave the way for magnesium-catalysed enantioselective ketone reduction
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A magnesium precatalyst for the highly enantioselective hydro-boration of CO bonds is reported. The mechanistic basis of the unprecedented selectivity of this transformation has been investi-gated experimentally by isolation of catalytic intermediates and theoretically by DFT calculations. The facile formation of a magnesium borohydride species is critical in overcoming competing pathways in the selectivity-determining insertion step.
- Vasilenko, Vladislav,Blasius, Clemens K.,Wadepohl, Hubert,Gade, Lutz H.
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supporting information
p. 1203 - 1206
(2020/02/04)
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- A General Regioselective Synthesis of Alcohols by Cobalt-Catalyzed Hydrogenation of Epoxides
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A straightforward methodology for the synthesis of anti-Markovnikov-type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)2 as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi-substituted internal and terminal epoxides, as well as a good functional-group tolerance. Various natural-product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate-to-excellent yields.
- Beller, Matthias,Junge, Kathrin,Leischner, Thomas,Li, Wu,Liu, Weiping
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supporting information
p. 11321 - 11324
(2020/05/16)
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- Manganese Catalyzed Asymmetric Transfer Hydrogenation of Ketones Using Chiral Oxamide Ligands
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The asymmetric transfer hydrogenation of ketones using isopropyl alcohol (IPA) as hydrogen donor in the presence of novel manganese catalysts is explored. The selective and active systems are easily generated in situ from [MnBr(CO)5] and inexpensive C2-symmeric bisoxalamide ligands. Under the optimized reaction conditions, the Mn-derived catalyst gave higher enantioselectivity compared with the related ruthenium catalyst.
- Schneek?nig, Jacob,Junge, Kathrin,Beller, Matthias
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supporting information
p. 503 - 507
(2019/02/26)
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- Mechanism-Based Enantiodivergence in Manganese Reduction Catalysis: A Chiral Pincer Complex for the Highly Enantioselective Hydroboration of Ketones
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A manganese alkyl complex containing a chiral bis(oxazolinyl-methylidene)isoindoline pincer ligand is a precatalyst for a catalytic system of unprecedented activity and selectivity in the enantioselective hydroboration of ketones, thus producing preparatively useful chiral alcohols in excellent yields with up to greater than 99 % ee. It is applicable for both aryl alkyl and dialkyl ketone reduction under mild reaction conditions (TOF >450 h?1 at ?40 °C). The earth-abundant base-metal catalyst operates at very low catalyst loadings (as low as 0.1 mol %) and with a high level of functional-group tolerance. There is evidence for the existence of two distinct mechanistic pathways for manganese-catalyzed hydride transfer and their role for enantiocontrol in the selectivity-determining step is presented.
- Vasilenko, Vladislav,Blasius, Clemens K.,Wadepohl, Hubert,Gade, Lutz H.
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supporting information
p. 8393 - 8397
(2017/07/11)
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- Iron Catalyzed Hydroboration of Aldehydes and Ketones
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We report an operationally convenient room temperature hydroboration of aldehydes and ketones employing Fe(acac)3 as precatalyst. The hydroboration of aldehydes and ketones proceeded efficiently at room temperature to yield, after work up, 1° and 2° alcohols; chemoselective hydroboration of aldehydes over ketones is attained under these conditions. We propose a σ-bond metathesis mechanism in which an Fe-H intermediate is postulated to be a key reactive species.
- Tamang, Sem Raj,Findlater, Michael
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p. 12857 - 12862
(2017/12/08)
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- Visible-Light-Mediated Anti-Markovnikov Hydration of Olefins
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Considering that stoichiometric borane and oxidant are required in the classical alkene anti-Markovnikov hydration process, it remains appealing to achieve the transformation in a catalytic protocol. Herein, a visible-light-mediated anti-Markovnikov addition of water to alkenes by using an organic photoredox catalyst in conjunction with a redox-active hydrogen atom donor was developed, which avoided the need for a transition-metal catalyst, stoichiometric borane, as well as oxidant. Both terminal and internal olefins are readily accommodated in this transformation to obtain corresponding primary and secondary alcohols in good yields with single regioselectivity. This procedure can be scaled up to gram scale with a 230 turnover number based on photocatalyst.
- Hu, Xia,Zhang, Guoting,Bu, Faxiang,Lei, Aiwen
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p. 1432 - 1437
(2017/08/09)
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- Chiral-at-metal iridium complex for efficient enantioselective transfer hydrogenation of ketones
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A bis-cyclometalated iridium(iii) complex with metal-centered chirality catalyzes the enantioselective transfer hydrogenation of ketones with high enantioselectivities at low catalyst loadings down to 0.002 mol%. Importantly, the rate of catalysis and enantioselectivity are markedly improved in the presence of a pyrazole co-ligand. The reaction is proposed to proceed via an iridium-hydride intermediate exploiting metal-ligand cooperativity (bifunctional catalysis).
- Tian, Cheng,Gong, Lei,Meggers, Eric
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supporting information
p. 4207 - 4210
(2016/03/19)
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- Cobalt-catalyzed asymmetric hydroboration of aryl ketones with pinacolborane
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The highly enantioselective cobalt-catalyzed hydroboration reaction of aryl ketones with HBpin was developed using iminopyridine oxazoline ligands. Halides, amines, ethers, sulfides, esters and amides are well tolerated under the mild reaction conditions, demonstrating its synthetic advantage. Substituted diaryl ketones could also be hydroborated with high enantioselectivity.
- Guo, Jun,Chen, Jianhui,Lu, Zhan
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supporting information
p. 5725 - 5727
(2015/03/30)
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- Method and apparatus for the synthesis of dihydroartemisinin and artemisinin derivatives
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The present invention is directed to a method for continuous production of dihydroartemisinin and also artemisinin derivatives derived from dihydroartemisinin by using artemisinin or dihydroartemisinic acid (DHAA) as starting material as well as to a continuous flow reactor for producing dihydroartemisinin as well as the artemisinin derivatives. It was found that the reduction of artemisinin to dihydroartemisinin in a continuous process requires a special kind of reactor and a special combination of reagents comprising a hydride reducing agent, at least one activator such as an inorganic activator, at least one solid base, at least one aprotic solvent and at least one C1-C5 alcohol.
- -
-
Paragraph 0185-0186
(2015/02/02)
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- Synthesis and characterization of novel chiral bidentate P,N-containing ligands and ruthenium(II) complex. the application in asymmetric transfer hydrogenation of ketones
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Novel chiral bidentate P,N-containing ligands have been easily synthesized by Schiff-base condensation of o-(diphenylphosphino)benzaldehyde and modified chiral diamine, (R,R)-2-(2,5-dimethyl-pyrrol-1-yl)-cyclohexylamine, further reduction with NaBH4. The chiral ruthenium(II) complex could be successfully prepared from the reaction between chiral bidentate aminophosphine ligand and RuCl2(PPh3)3. The chiral bidentate P,N-containing ligands and ruthenium(II) complex were fully characterized by NMR, IR, HRMS and single-crystal X-ray diffraction studies. In the presence of KOH, the asymmetric transfer hydrogenation (ATH) of various ketones catalyzed by the chiral ruthenium(II) complex proceeded smoothly under mild conditions, affording corresponding chiral secondary alcohols with up to 99% conversion and up to 60% ee. Additive such as NH4I was found to be helpful to promoting the enantioselectivity.
- Zeng, Li,Wu, Fang,Li, Yan-Yun,Dong, Zhen-Rong,Gao, Jing-Xing
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supporting information
p. 34 - 39
(2014/05/20)
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- Iron catalyzed asymmetric hydrogenation of ketones
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Chiral molecules, such as alcohols, are vital for the manufacturing of fine chemicals, pharmaceuticals, agrochemicals, fragrances, and novel materials. These molecules need to be produced in high yield and high optical purity and preferentially catalytically. Among all the asymmetric catalytic reactions, asymmetric hydrogenation with H2 (AH) is the most widely used in the industry. With few exceptions, these AH processes use catalysts based on the three critical metals, rhodium, ruthenium, and iridium. Herein we describe a simple, industrially viable iron catalyst that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts. By combining a chiral, 22-membered macrocyclic ligand with the cheap, readily available Fe 3(CO)12, a wide variety of ketones have been hydrogenated under 50 bar H2 at 45-65 C, affording highly valuable chiral alcohols with enantioselectivities approaching or surpassing those obtained with the noble metal catalysts. In contrast to AH by most noble metal catalysts, the iron-catalyzed hydrogenation appears to be heterogeneous.
- Li, Yanyun,Yu, Shenluan,Wu, Xiaofeng,Xiao, Jianliang,Shen, Weiyi,Dong, Zhenrong,Gao, Jingxing
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supporting information
p. 4031 - 4039
(2014/04/03)
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- Continuous reductions and reductive aminations using solid NaBH4
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Most successful reactions carried out under continuous flow conditions mix homogeneous solutions yielding homogeneous products. Using solids is avoided to prevent pump and reactor clogging; even though solid reagents may often be the best choice for a given transformation. Here we demonstrate that by pumping aldehydes, ketones, or in situ formed imines through a specially formulated NaBH4 column results in efficient reductions. The column design and performance characteristics, along with substrate scope, are discussed.
- Gilmore, Kerry,Vukeli, Stella,McQuade, D. Tyler,Koksch, Beate,Seeberger, Peter H.
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p. 1771 - 1776
(2015/02/02)
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- Enantioselective oxidation of racemic secondary alcohols catalyzed by chiral Mn(iii)-salen complexes with N-bromosuccinimide as a powerful oxidant
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We demonstrate an efficient enantioselective oxidation of secondary alcohols catalyzed by Mn(iii)-salen complex using N-bromosuccinimide (NBS) as the oxidant. The new protocol is very efficient for the oxidative kinetic resolution of a variety of secondary alcohols, including ortho-substituted benzylic alcohols. The Royal Society of Chemistry 2012.
- Xu, Daqian,Wang, Shoufeng,Shen, Zhiqiang,Xia, Chungu,Sun, Wei
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supporting information
p. 2730 - 2732
(2012/11/07)
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- Oxidative kinetic resolution of racemic secondary alcohols in water with chiral PNNP/Ir catalyst
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Using water as solvent, the oxidative kinetic resolution of a wide range of racemic secondary alcohols with a chiral PNNP/Ir catalyst was investigated. The catalytic reaction proceeded smoothly with excellent enantioselectivity (up to 97% ee) under mild conditions, providing an environmentally benign process to achieve optically active alcohols.
- Zhang, Juanni,Yang, Xiangren,Zhou, Han,Li, Yanyun,Dong, Zhenrong,Gao, Jingxing
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p. 1289 - 1292
(2012/06/18)
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- Synthesis of novel chiral tetraaza ligands and their application in enantioselective transfer hydrogenation of ketones
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Novel chiral tetraaza ligands (R)-N, N′-bis[2-(piperidin-1-yl) benzylidene]propane-1, 2-diamine 6 and (S)-N-[2-(piperidin-1-yl)benzylidene]-3- {[2-(piperidin-1-yl)benzylidene]amino}-alanine sodium salt 7 have been synthesized and fully characterized by NM
- Yu, Shen Luan,Li, Yan Yun,Dong, Zhen Rong,Gao, Jing Xing
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scheme or table
p. 395 - 398
(2012/06/18)
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- Competitive enantiodifferentiating anti-Markovnikov photoaddition of water and methanol to 1,1-diphenylpropene using a sensitizing cyclodextrin host
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(Chemical Equation Presented) UV-vis, circular dichroism (CD), fluorescence, and NMR spectral studies on the self-inclusion behavior of a newly synthesized sensitizing host, 6-(5-cyanonaphthyl-1-carboamido)-6-deoxy-β- cyclodextrin (1), showed that the app
- Fukuhara, Gaku,Mori, Tadashi,Inoue, Yoshihisa
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experimental part
p. 6714 - 6727
(2009/12/30)
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- Highly efficient iridium catalyst for asymmetric transfer hydrogenation of aromatic ketones under base-free conditions
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(Chemical Equation Presented) Catalytic systems generated in situ from the chiral PNNP ligands with iridium or rhodium hydride complexes exhibited excellent catalytic activity and good enantioselectivity in the asymmetric transfer hydrogenation of aromati
- Dong, Zhen-Rong,Li, Yan-Yun,Chen, Jian-Shan,Li, Bao-Zhu,Xing, Yan,Gao, Jing-Xing
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p. 1043 - 1045
(2007/10/03)
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- Asymmetric transfer hydrogenation of aromatic ketones catalyzed by the iridium hydride complex under ambient conditions
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The chiral Ir catalytic system generated in situ from iridium hydride complex and chiral diaminodiphosphine ligand was employed in asymmetric transfer hydrogenation of aromatic ketones to give the corresponding optically active alcohols, with up to 99% ee
- Chen, Jian-Shan,Li, Yan-Yun,Dong, Zhen-Rong,Li, Bao-Zhu,Gao, Jing-Xing
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p. 8415 - 8418
(2007/10/03)
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- Highly enantioselective lipase-catalyzed reactions at high temperatures up to 120°C in organic solvent
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Lipase-catalyzed kinetic resolutions of 1,1-diphenyl-2-propanol were performed at high temperatures up to 120°C. Burkholderia cepacia lipase immobilized on porous ceramic particles, lipase PS-C II (Amano Enzyme Inc.), gave an enantiopure product at 40-120
- Ema, Tadashi,Kageyama, Masafumi,Korenaga, Toshinobu,Sakai, Takashi
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p. 3943 - 3947
(2007/10/03)
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- Palladium-catalyzed aerobic oxidative kinetic resolution of alcohols with an achiral exogenous base
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Substitution of exogenous (-)-sparteine for a more practical achiral base in the aerobic oxidative kinetic resolution of secondary alcohols is described. Carbonate bases are the most effective of those screened and allow for effective kinetic resolution of benzylic, allylic, and aliphatic substrates. The procedure was also successfully extended to the oxidative desymmetrization of meso diols.
- Mandal, Sunil K.,Sigman, Matthew S.
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p. 7535 - 7537
(2007/10/03)
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- Scope of enantioselective Palladium(II)-catalyzed aerobic alcohol oxidations with (-)-sparteine
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Evaluation of the substrate scope for Pd(II)/ (-)-sparteine catalyzed aerobic oxidative kinetic resolution of secondary alcohols is disclosed. An improved system is found with use of tert-butyl alcohol solvent in which benzylic and aliphatic alcohols as well as alcohols containing olefins are effectively oxidatively resolved. For substrates that successfully undergo oxidative kinetic resolution, krel values are generally between 10 and 20. Successful scale-up of various substrates to 10-mmol scale is described. Extension to oxidative desymmetrization of 1,3-meso-diols is successful with enantiomeric excesses ranging from 78 to 85%.
- Mandal, Sunil K.,Jensen, David R.,Pugsley, Jacob S.,Sigman, Matthew S.
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p. 4600 - 4603
(2007/10/03)
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- Compensation effect between differential activation enthalpy and entropy in subtilisin-catalyzed kinetic resolutions of secondary alcohols
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Thermodynamic parameters for subtilisin-catalyzed kinetic resolutions of secondary alcohols were determined, and a compensation effect between ΔΔH? and ΔΔS? was found. These data are explained in terms of the transition-state model.
- Ema, Tadashi,Yamaguchi, Kunihiro,Wakasa, Yuji,Tanaka, Nobuaki,Utaka, Masanori,Sakai, Takashi
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p. 782 - 783
(2007/10/03)
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- Enzymatic resolution of hindered secondary alcohols: Efficient access to a new simplified chiral auxiliary
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2,2-Diphenylcyclopentanol, an efficient chiral auxiliary which bears only one stereogenic center, as well as some related hindered secondary alcohols, were resolved by means of pig liver acetone powder (PLAP) and horse liver acetone powder (HLAP).
- Randrianasolo-Rakotozafy,Azerad,Dumas,Potin,D'Angelo
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p. 761 - 766
(2007/10/02)
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- Photosensitized (electron transfer) carbon-carbon bond cleavage of radical cations: the 2-phenylethyl ether and acetal systems
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The scope of the photosensitized (electron transfer) carbon-carbon bond cleavage involving radical cations has been defined for 2-phenylethyl ethers and acetals.The thresholds for reactivity of the monophenylethyl and gem-diphenylethyl derivatives are compared.While the radical cation of methyl 2,2-diphenylethyl ether (7) cleaves to give ultimately diphenylmethane (2) and dimethoxymethane (8), the radical cation of methyl 2-phenylethyl ether (9) was stable under these conditions.In contrast to the lack of reactivity of the radical cation of 9, the radical cations of methyl 2-phenyl-2-propyl ether (11), methyl 2-phenylcyclopentyl ether (13), and 2-phenylmethyl-1,3-dioxolane (16) cleave.Cleavage in the monophenylethyl series is limited to formation of a carbocation at least as stable as the secondary α-oxyalkyl or di-α-oxyalkyl.The basis for predicting this type of reactivity of radical cations is defined.The rate of carbon-carbon bond cleavage is increased the oxidation potential of the molecule, by decreasing the carbon-carbon bond strength, and (or) by decreasing the oxidation potential of that fragment that will become the carbocation.The results obtained from the reactions of 2-diphenylmethyl-1,3-dioxolane (14) and 2-phenylmethyl-1,3-dioxolane (16) cast doubt on the published oxidation potential for the 1,3-dioxolan-2-yl radical.Key words: photochemistry, radical cation, electron transfer, bond cleavage, radical.
- Arnold, Donald R.,Lamont, Laurie J.
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p. 2119 - 2127
(2007/10/02)
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- Temperature and Substituent Effects on Regioselectivity in the Insertion of Arylcarbene into Alcohols
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Photolysis of aryldiazomethanes in methanol, ethanol, and 2-propanol gave OH insertion products along with small amounts of CH insertion products at ambient temperature.However, the CH insertion products increased significantly at the expense of the ether as the temperature was lowered.The attempted sensitized decomposition of the diazomethane did not lead to an increase in the CH insertion products presumably because of a rapid singlet-triplet equilibrium.The key intermediate leading to the CH insertion is suggested to be ground-state triplet arylcarbene, based on the accumulated spectroscopic as well as chemical evidence for the intervention of the triplet arylcarbene in the low-temperature photolysis of aryldiazomethanes.Substituents on the phenyl ring also have an appreciable effect on the insertion selectivity.At room temperature, the OH/CH insertion selectivity increased with the electron-donating ability of the substituents.This is interpreted in terms of the substituent effect on the transition state of OH insertion, where there is a deficiency of electrons at the benzylic carbon atom, rather than on the stability of singlet carbene.At low temperature, both electron-donating and -withdrawing substituents facilitate OH insertion, indicating the change in substituents induces a concomitant change in the insertion mechanism, presumably due to decreasing nucleophilicity of carbene with increasing electron-withdrawing ability as well as decreasing proton-donor activity of alcohol with decreasing temperature.This may also reflect the effect of the substituent on the singlet-triplet energy gap.
- Tomioka, Hideo,Suzuki, Shinji,Izawa, Yasuji
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p. 3156 - 3162
(2007/10/02)
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- Reactivity of Ketones in Homogeneous Catalytic Hydrogenation with Cationic Rhodium Complexes
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The catalytic hydrogenation of several ketones with cationic rhodium complexes has been investigated at 30 deg C with hydrogen at atmospheric pressure.The rate of the reaction depended very much on the structure of both the ketone and phosphine ligand, with triethylphosphine giving the highest activity among the ligands used.An electron-withdrawing substituent in the ketone was found to increase its reactivity among both alkyl and aryl ketones; the rates of reaction of the former ketones were generally faster.Benzyl methyl ketone showed a very high reactivity among aryl ketones, suggesting that the phenyl group may be in a position to interact with the rhodium atom to enhance the reactivity.Unsaturated ketones are hydrogenated catalytically to yield saturated ketones first, which are further hydrogenated to corresponding saturated alcohols.No trace of unsaturated alcohol was observed in this hydrogenation, even when the hydrogenation rate of the olefinic bond in the unsaturated ketone was much smaller than that of the carbonyl group of the corresponding saturated ketone in the consecutive hydrogenation.The reactivities of ketones are discussed in connection with their co-ordination and the hydrogenation mechanisms.
- Fujitsu, Hiroshi,Matsumura, Eiichi,Takeshita, Kenjiro,Mochida, Isao
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p. 2650 - 2655
(2007/10/02)
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- The Low-temperature Photolysis of Diazo Compounds. The Utility of Tertiary Alcohol in Matrix Studies of Carbene Chemistry
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Carbene processes within the t-BuOH matrix at -196 deg C were investigated in order to show the utility of the matrix as a tool for the study of carbene chemistry.The photolysis of several aryldiazomethane derivatives in the t-BuOH matrix gave the olefinic dimer as the main product, probably arising from a combination of two triplet arylcarbenes in the aggregate of molecules.The similar photolysis of other diazo compounds (e.g., N2CHCOR, R = OR', NEt2, and Ph) resulted in no detection of the olefinic dimer.This was explained in terms of the structural effect on the ground-state multiplicity of carbene.The photolysis of Ph2CN2 in t-BuOH containing 5percent EtOH at -196 deg C gave almost exclusively O-H and C-H insertion products with the solute alcohol at the expense of the O-H insertion product with the host, i.e., Ph2CHOBut, which was the major product in the liquid-phase photolysis.This is ascribable to the co-aggregation of the carbene precursor with the solute alcohol because of the relatively large guest hole provided by the bulky tertiary alcohol matrix.A more general utility of this matrix was shown in the reaction of Ph2C with Ph2CO to give oxirane, in which the intervention of carbonyl ylide was demonstrated at low temperatures.
- Tomioka, Hideo,Miwa, Takaaki,Suzuki, Shinji,Izawa, Yasuji
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p. 753 - 756
(2007/10/02)
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