- New Generation Method for a Samarium(II) Equivalent: Me3SiX (X = Br and I)/Sm-Assisted Intermolecular Carbon-Carbon Bond Forming Reactions for Carbonyl Compounds
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Samarium(II) species can be efficiently generated in situ from a reaction between elemental samarium and chlorotrimethylsilane (Me3SiCl)/sodium iodide (NaI) reagent or bromotrimethylsilane (Me3SiBr) in acetonitrile.The reductive coupling reaction of carbonyl compounds was achieved by the action of Sm(II) reagent thus generated from Sm/Me3SiCl/NaI or Sm/Me3SiBr to give the corresponding pinacol products in moderate to high yields.The samarium(II) reagent induced the intermolecular coupling reaction of α,β-unsaturated esters with carbonyl compounds or imines followed by intramolecular cyclization to form the corresponding γ-lactones or γ-lactams in moderate yields.The reaction of α-bromo esters with carbonyl compounds using the Sm(II) species, generated from the Sm/Me3SiX system, led to the corresponding β-hydroxy esters in 52-95percent yields.
- Akane, Noriyuki,Hatano, Tadashi,Kusui, Hiroko,Nishiyama, Yutaka,Ishii, Yasutaka
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Read Online
- Intramolecular and intermolecular ketone-ester reductive coupling reactions promoted by samarium(II) iodide
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Intramolecular and intermolecular ketone-ester reductive coupling reactions promoted by SmI2 have been studied. Substituted 2-hydroxy-5-ethoxycarbonylcyclopentanones, 5-ethoxycarbonylcyclopentenones and α-ketols were prepared in moderate to good yields at room temperature or under reflux under neutral conditions.
- Liu, Yunkui,Zhang, Yongmin
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- A Simple and Efficient New Synthesis of Vicinal Diols by Reductive Coupling of Carbonyl Compounds
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A universally applicable, new 'pinacolic reduction' for aldehydes and ketones is described.
- Csuk, Rene,Fuerstner, Alois,Weidmann, Hans
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Read Online
- A new preparation of samarium dibromide and its use in stoichiometric and catalytic pinacol coupling reactions
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A new convenient preparation of samarium dibromide in THF is reported. Pinacol coupling reactions using SmBr2 in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonyl compounds.
- Hélion, Florence,Lannou, Marie-Isabelle,Namy, Jean-Louis
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Read Online
- Radical pairs with rotational fluidity in the photochemical reaction of acetophenone and cyclohexane in the zeolite NAY: A 13C CPMAS NMR and product analysis study
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The photochemical reaction of acetophenone and cyclohexane in the zeolite NaY occurs by combination of the geminate radical pairs to give products that reveal a significant amount of rotational fluidity, which was also documented by intermolecular nuclear dipolar interaction measurements using cross polarization 13C NMR (CPMAS) experiments. The Royal Society of Chemistry 2009.
- Amboya, Ammee,Nguyen, Tina,Huynh, Hien T.,Brown, Ashley,Ratliff, Gretchen,Yonutas, Heather,Cizmeciyan, Deniz,Natarajan, Arunkumar,Garcia Garibay, Miguel A.
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- Samarium(II) iodide promoted novel reductive coupling reactions of ketones and nitriles
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The intramolecular and intermolecular reductive coupling reaction of ketones-nitriles promoted by SmI2 were studied.
- Zhou, Longhu,Zhang, Yongmin,Shi, Daqing
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Read Online
- Diastereoselective pinacol coupling of alkyl aryl ketones with rare earth metals in the presence of chlorosilanes
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Rare earth metals (Ln) are found to act as useful reducing agents for the pinacol coupling reaction of alkyl aryl ketones in the presence of chlorosilanes. Although the hitherto known pinacol coupling reaction using rare earth reducing agents generally exhibits very low diastereoselectivities, the present pinacol coupling by use of a Ln/R3SiCl system usually indicates higher diastereoselectivities. In particular, a Yb/Me3SiCl system attains the diastereoselective pinacol coupling of primary alkyl aryl ketones with the dl/meso ratio of 8/2~9/1.
- Ogawa, Akiya,Takeuchi, Hiroki,Hirao, Toshikazu
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Read Online
- A convenient pinacol coupling of diaryl ketones with B2pin2viapyridine catalysis
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A convenient, pyridine-boryl radical-mediated pinacol coupling of diaryl ketones is developed. In contrast to the conventional pinacol coupling that requires sensitive reducing metal, the current method employs a stable diboron reagent and pyridine Lewis base catalyst for the generation of a ketyl radical. The newly developed process is operationally simple, and the desired diols are produced with excellent efficiency in up to 99% yield within 1 hour. The superior reactivity of diaryl ketone was observed over monoaryl carbonyl compounds and analyzed by DFT calculations, which suggests the necessity of both aromatic rings for the maximum stabilization of the transition states.
- Jo, Junhyuk,Kim, Seonyul,Choi, Jun-Ho,Chung, Won-Jin
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supporting information
p. 1360 - 1363
(2021/02/22)
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- Thio-assisted reductive electrolytic cleavage of lignin β-O-4 models and authentic lignin
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Avoiding the use of expensive catalysts and harsh conditions such as elevated temperatures and high pressures is a critical goal in lignin depolymerization and valorization. In this study, we present a thio-assisted electrocatalytic reductive approach using inexpensive reticulated vitreous carbon (RVC) as the working cathode to cleave the β-O-4-type linkages in keto aryl ethers. In the presence of a pre-electrolyzed disulfide (2,2′-dithiodiethanol) and a radical inhibitor (BHT) at room temperature at a current density of 2.5 mA cm-2, cathodic reduction of nonphenolic β-O-4 dimers afforded over 90% of the corresponding monomeric C-O cleavage products in only 1.5 h. Extended to DDQ-oxidized poplar lignin, this combination of electric current and disulfide, applied over 6 h, released 36 wt% of ethyl acetate soluble fragments and 26 wt% of aqueous soluble fragments, leaving only 38 wt% of insoluble residue. These findings represent a significant improvement over the current alone values (24 wt% ethyl acetate soluble; 22 wt% aqueous soluble; 54 wt% insoluble residue) and represent an important next step in our efforts to develop a mild electrochemical method for reductive lignin deconstruction.
- Fang, Zhen,Flynn, Michael G.,Jackson, James E.,Hegg, Eric L.
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p. 412 - 421
(2021/01/28)
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- Luminescent tungsten(vi) complexes as photocatalysts for light-driven C-C and C-B bond formation reactions
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The realization of photocatalysis for practical synthetic application hinges on the development of inexpensive photocatalysts which can be prepared on a large scale. Herein an air-stable, visible-light-absorbing photoluminescent tungsten(vi) complex which can be conveniently prepared at the gram-scale is described. This complex could catalyse photochemical organic transformation reactions including borylation of aryl halides, such as aryl chloride, reductive coupling of benzyl bromides for C-C bond formation, reductive coupling of phenacyl bromides, and decarboxylative coupling of redox-active esters of alkyl carboxylic acid with high product yields and broad functional group tolerance.
- Chan, Kaai-Tung,Che, Chi-Ming,Du, Lili,Liu, Yungen,Phillips, David Lee,To, Wai-Pong,Tong, Glenna So Ming,Wu, Liang-Liang,Yu, Daohong
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p. 6370 - 6382
(2020/07/15)
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- Multiple Mechanisms Mapped in Aryl Alkyl Ether Cleavage via Aqueous Electrocatalytic Hydrogenation over Skeletal Nickel
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We present here detailed mechanistic studies of electrocatalytic hydrogenation (ECH) in aqueous solution over skeletal nickel cathodes to probe the various paths of reductive catalytic C-O bond cleavage among functionalized aryl ethers relevant to energy science. Heterogeneous catalytic hydrogenolysis of aryl ethers is important both in hydrodeoxygenation of fossil fuels and in upgrading of lignin from biomass. The presence or absence of simple functionalities such as carbonyl, hydroxyl, methyl, or methoxyl groups is known to cause dramatic shifts in reactivity and cleavage selectivity between sp3 C-O and sp2 C-O bonds. Specifically, reported hydrogenolysis studies with Ni and other catalysts have hinted at different cleavage mechanisms for the C-O ether bonds in α-keto and α-hydroxy β-O-4 type aryl ether linkages of lignin. Our new rate, selectivity, and isotopic labeling results from ECH reactions confirm that these aryl ethers undergo C-O cleavage via distinct paths. For the simple 2-phenoxy-1-phenylethane or its alcohol congener, 2-phenoxy-1-phenylethanol, the benzylic site is activated via Ni C-H insertion, followed by beta elimination of the phenoxide leaving group. But in the case of the ketone, 2-phenoxyacetophenone, the polarized carbonyl πsystem apparently binds directly with the electron rich Ni cathode surface without breaking the aromaticity of the neighboring phenyl ring, leading to rapid cleavage. Substituent steric and electronic perturbations across a broad range of β-O-4 type ethers create a hierarchy of cleavage rates that supports these mechanistic ideas while offering guidance to allow rational design of the catalytic method. On the basis of the new insights, the usage of cosolvent acetone is shown to enable control of product selectivity.
- Hegg, Eric L.,Jackson, James E.,Klinger, Grace E.,Saffron, Christopher M.,Zhou, Yuting
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p. 4037 - 4050
(2020/03/10)
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- How the sustainable solvent water unleashes the photoredox catalytic potential of ruthenium polypyridyl complexes for pinacol couplings
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By complementing laser flash photolysis with product studies in visible-LED driven syntheses, we show that the one-electron reduced forms OER of tris(2,2′-bipyridine)ruthenium(ii) and its more reactive derivative with 4,4′-dimethylated ligands exhibit a reductive power greater by 0.2 eV in water than in acetonitrile; and that this difference allows the reduction of carbonyl compounds, and thus pinacol couplings, in aqueous medium via ruthenium-based photoredox catalysis as an alternative to using more expensive and less photostable higher-energy complexes (e.g., of iridium). Ascorbate serves as sacrificial donor to access OER. SDS micelles or cyclodextrins as carriers help overcome solubility problems of less hydrophilic substrates, and more reactive water-soluble substrates can even be coupled at neutral pH, such that the mild conditions make the process fully sustainable.
- Naumann, Robert,Goez, Martin
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p. 4470 - 4474
(2019/08/21)
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- Bifunctional copper-based photocatalyst for reductive pinacol-type couplings
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A bifunctional copper-based photocatalyst has been prepared that employs a pyrazole-pyridine ligand incorporating a sulfonamide moiety that functions as an intramolecular hydrogen-bond donor for a photochemical PCET process. In typical reductive PCET processes, the photocatalyst and H-bond donor must have an appropriate redox potential and pKa, respectively, to promote the PCET. When working in concert in a bifunctional catalyst such as Cu(pypzs)(BINAP)BF4, the pKa of the H-bond donor can have an acidity that is orders of magnitude less and still efficiently promote the PCET process. A reductive pinacol-type coupling can be performed using a base-metal derived photocatalyst to afford valuable diols (24 examples, 46-99% yield), from readily available aldehydes and ketones.
- Caron, Antoine,Morin, émilie,Collins, Shawn K.
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p. 9458 - 9464
(2019/10/11)
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- Light-enabled metal-free pinacol coupling by hydrazine
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Efficient carbon-carbon bond formation is of great importance in modern organic synthetic chemistry. The pinacol coupling discovered over a century ago is still one of the most efficient coupling reactions to build the C-C bond in one step. However, traditional pinacol coupling often requires over-stoichiometric amounts of active metals as reductants, causing long-lasting metal waste issues and sustainability concerns. A great scientific challenge is to design a metal-free approach to the pinacol coupling reaction. Herein, we describe a light-driven pinacol coupling protocol without use of any metals, but with N2H4, used as a clean non-metallic hydrogen-atom-transfer (HAT) reductant. In this transformation, only traceless non-toxic N2 and H2 gases were produced as by-products with a relatively broad aromatic ketone scope and good functional group tolerance. A combined experimental and computational investigation of the mechanism suggests that this novel pinacol coupling reaction proceeds via a HAT process between photo-excited ketone and N2H4, instead of the common single-electron-transfer (SET) process for metal reductants.
- Qiu, Zihang,Pham, Hanh D. M.,Li, Jianbin,Li, Chen-Chen,Castillo-Pazos, Durbis J.,Khaliullin, Rustam Z.,Li, Chao-Jun
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p. 10937 - 10943
(2019/12/23)
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- Efficient acceptorless photo-dehydrogenation of alcohols and: N -heterocycles with binuclear platinum(ii) diphosphite complexes
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Although photoredox catalysis employing Ru(ii) and Ir(iii) complexes as photocatalysts has emerged as a versatile tool for oxidative C-H functionalization under mild conditions, the need for additional reagents acting as electron donor/scavenger for completing the catalytic cycle undermines the practicability of this approach. Herein we demonstrate that photo-induced oxidative C-H functionalization can be catalysed with high product yields under oxygen-free and acceptorless conditions via inner-sphere atom abstraction by binuclear platinum(ii) diphosphite complexes. Both alcohols (51 examples), particularly the aliphatic ones, and saturated N-heterocycles (24 examples) can be efficiently dehydrogenated under light irradiation at room temperature. Regeneration of the photocatalyst by means of reductive elimination of dihydrogen from the in situ formed platinum(iii)-hydride species represents an alternative paradigm to the current approach in photoredox catalysis.
- Zhong, Jian-Ji,To, Wai-Pong,Liu, Yungen,Lu, Wei,Che, Chi-Ming
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p. 4883 - 4889
(2019/05/16)
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- Organic photoredox catalyst with substrate-capture ability: A perylene derivative bearing urethane moiety for reductive coupling of ketones and aldehydes under visible light
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A perylene derivative bearing a urethane moiety served as an efficient photoredox catalyst for the reductive coupling of ketones and aldehydes under visible light, implicating that the urethane moiety captured substrates through hydrogen bonds to lower the LUMO levels of the captured substrates, thus promoting single electron transfer from the reductant anion radical of the perylene moiety to the substrates.
- Okamoto, Shusuke,Tsujioka, Hiroki,Sudo, Atsushi
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supporting information
p. 369 - 372
(2018/03/05)
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- Lewis Acid Assisted Electrophilic Fluorine-Catalyzed Pinacol Rearrangement of Hydrobenzoin Substrates: One-Pot Synthesis of (±)-Latifine and (±)-Cherylline
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A microwave-irradiated solvent-free pinacol rearrangement of hydrobenzoin substrates catalyzed by a combination of N-fluorobenzenesulfonimide and FeCl3·6H2O was developed. Its selectivity was first investigated by density functional theory (DFT) calculations. Then the functional group tolerance was examined by synthesizing a series of substrates designed based on the insight provided by the DFT calculations. The application of the methodology was demonstrated by the efficient one-pot synthesis of (±)-latifine and (±)-cherylline, both are 4-aryltetrahydroisoquinoline alkaloids isolated from Amaryllidacecae plants.
- Shi, Hui,Du, Chuan,Zhang, Xinhang,Xie, Fukai,Wang, Xiaoyu,Cui, Shanshan,Peng, Xiaoshi,Cheng, Maosheng,Lin, Bin,Liu, Yongxiang
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p. 1312 - 1319
(2018/02/09)
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- Air-Stable Blue Phosphorescent Tetradentate Platinum(II) Complexes as Strong Photo-Reductant
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Strong photo-reductants have applications in photo-redox organic synthesis involving reductive activation of C?X(halide) and C=O bonds. We report herein air-stable PtII complexes supported by tetradentate bis(phenolate-NHC) ligands having peripheral electron-donating N-carbazolyl groups. Photo-physical, electrochemical, and computational studies reveal that the presence of N-carbazolyl groups enhances the light absorption and redox reversibility because of its involvement into the frontier MOs in both ground and excited states, making the complexes robust strong photo-reductant with E([Pt]+/*) over ?2.6 V vs. Cp2Fe+/0. The one-electron reduced [Pt]? species are stronger reductants with EPC([Pt]0/?) up to ?3.1 V vs. Cp2Fe+/0. By virtue of the strong reducing nature of these species generated upon light excitation, they can be used in light-driven reductive coupling of carbonyl compounds and reductive debromination of a wide range of unactivated aryl bromides.
- Li, Kai,Wan, Qingyun,Yang, Chen,Chang, Xiao-Yong,Low, Kam-Hung,Che, Chi-Ming
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supporting information
p. 14129 - 14133
(2018/10/15)
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- Feasibility of room temperature reduction of aromatic carbonyl and nitro compounds by Zn/dil. HCl-Et2O system: An experimental and DFT study
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This experimental study is about the feasibility of the room temperature reduction of the ether soluble aromatic carbonyl/nitro compounds by atomic hydrogen. The atomic hydrogen is produced by the novel Zn/dil. HCl-Et2O reducing system (wherein dil. HCl is slowly added to the ethereal solution of Zn and substrate).This study resulted in single or mixture of anticipated reduced products in different yields. The DFT study with B3LYP/6.311g ++ (d,p) basis set revealed that the stability of the first formed free radical (energy factor) and the homo nuclear nature of the carbonyl and nitro group (charge factor) decide the yield. It is also found that the presence of –M group at o- or p- position to the carbonyl/nitro group results in the favourable modification of above-mentioned factors. The above-mentioned factors also explain the preferential reduction of nitro group when it is present along with carbonyl group. The free radical mechanism was confirmed by the formation of pinacol coupled product in one instance. In one of the reduction reactions, an unreported compound viz. the dimer of o-amino benzaldehyde was obtained in good yield.
- Rajamathe,Selvaraj
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p. 1761 - 1766
(2017/06/27)
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- Alkene Metalates as Hydrogenation Catalysts
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First-row transition-metal complexes hold great potential as catalysts for hydrogenations and related reductive reactions. Homo- and heteroleptic arene/alkene metalates(1?) (M=Co, Fe) are a structurally distinct catalyst class with good activities in hydrogenations of alkenes and alkynes. The first syntheses of the heteroleptic cobaltates [K([18]crown-6)][Co(η4-cod)(η2-styrene)2] (5) and [K([18]crown-6)][Co(η4-dct)(η4-cod)] (6), and the homoleptic complex [K(thf)2][Co(η4-dct)2] (7; dct=dibenzo[a,e]cyclooctatetraene, cod=1,5-cyclooctadiene), are reported. For comparison, two cyclopentadienylferrates(1?) were synthesized according to literature procedures. The isolated and fully characterized monoanionic complexes were competent precatalysts in alkene hydrogenations under mild conditions (2 bar H2, r.t., THF). Mechanistic studies by NMR spectroscopy, ESI mass spectrometry, and poisoning experiments documented the operation of a homogeneous mechanism, which was initiated by facile redox-neutral π-ligand exchange with the substrates followed by H2 activation. The substrate scope of the investigated precatalysts was also extended to polar substrates (ketones and imines).
- Büschelberger, Philipp,G?rtner, Dominik,Reyes-Rodriguez, Efrain,Kreyenschmidt, Friedrich,Koszinowski, Konrad,Jacobi von Wangelin, Axel,Wolf, Robert
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p. 3139 - 3151
(2017/03/13)
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- Comparison of photochemical reactions of aromatic carbonyl compounds with a silyl ketene thioacetal and a silyl ketene acetal
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Photoaddition reactions of carbonyl compounds with silyl ketene thioacetals have been explored and the results are compared to those arising from investigations of analogus reactions with silyl ketene acetals. Observations made in this study show that photoirradiation of benzaldehyde (8) and benzophenone (9) and with the dimethyl substituted silyl ketene thioacetal (13) promotes reactions that take place predominantly via Paterno-Büchi type [2+2]-cycloaddition pathways to produce oxetanes. In addition, photoreactions between acetophenone (10) and p-cyanoacetophenone ( 11) and 13 occur via competitive sequential single electron transfer (SET)-desilylation or [2+2]-cycloaddition modes. Lastly, photochemical reaction of the highly electron deficient carbonyl compound, p-trifluoromethylacetophenone (12), and 13 gives rise to exclusive formation of β-hydroxythioester arising via the SET pathway. In contrast, photochemical reactions of all of these aromatic carbonyl compounds with the analogous dimethyl substituted silyl ketene acetal 14 take place predominantly via a sequential SET-desilylation pathway to form β-hydroxyesters. A comparison of these results reveals that replacement of an alkoxy by alkylthio group in the ketene derivatives brings about dramatic changes in chemoselectivities of the photoreactions with aryl-substituted ketones.
- Moon, Gyeong Min,Lim, Suk Hyun,Cho, Dae Won,Kim, Sung Hong,Lee, In Ok,Yoon, Ung Chan,Mariano, Patrick S.
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p. 978 - 988
(2015/03/04)
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- Photoredox-Catalyzed Reductive Coupling of Aldehydes, Ketones, and Imines with Visible Light
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Ketyl radical and amino radical anions, valuable reactive intermediates for C-C bond-forming reactions, are accessible through a C=O/C=NR umpolung. However, their utilization in catalysis remains largely underdeveloped owing to the high reduction potential of carbonyl compounds and imines. In the context of photoredox catalysis, tertiary amines are commonly employed as sacrificial co-reducing agents. Herein, an additional role of the amine is proposed, in which it is essential for the organocatalytic substrate activation. The combination of photoredox catalysis and carbonyl/imine activation enables the reductive coupling of aldehydes, ketones, and imines under mild reaction conditions.
- Nakajima, Masaki,Fava, Eleonora,Loescher, Sebastian,Jiang, Zhen,Rueping, Magnus
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p. 8828 - 8832
(2015/11/27)
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- Simple and expeditious pinacol coupling of non usual α,β-unsaturated carbonyl compounds in water
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Using zinc (0) in a 5% v AcOH aqueous solution allowed the efficient pinacol coupling of aliphatic or aromatic unusual, α,β-unsaturated carbonyl compounds such as citral A in good to excellent yields (56-99%). It can also be successfully applied to acetophenone.
- Billamboz, Muriel,Sotto, Nicolas,Chevrin-Villette, Carole,Len, Christophe
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p. 46026 - 46030
(2015/06/08)
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- Electrochemical reduction of aromatic ketones in 1-butyl-3-methylimidazolium-based ionic liquids in the presence of carbon dioxide: the influence of the ketone substituent and the ionic liquid anion on bulk electrolysis product distribution
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Electrochemical reduction of aromatic ketones, including acetophenone, benzophenone and 4-phenylbenzophenone, has been undertaken in 1-butyl-3-methylimidazolium-based ionic liquids containing tetrafluoroborate ([BF4]-), trifluoromethanesulfonate ([TfO]-) and tris(pentafluoroethyl)trifluorophosphate ([FAP]-) anions in the presence of carbon dioxide in order to investigate the ketone substituent effect and the influence of the acidic proton on the imidazolium cation (C2-H) on bulk electrolysis product distribution. For acetophenone, the minor products were dimers (50%) derived from proton coupled electron transfer reactions involving the electrogenerated radical anions and C2-H. In the cases of both acetophenone and benzophenone, the product distribution is essentially independent of the ionic liquid anion. By contrast, 4-phenylbenzophenone shows a product distribution that is dependent on the ionic liquid anion. Higher yields of carboxylic acids (~40%) are obtained with [TfO]- and [FAP]- anions because in these ionic liquids the C2-H is less acidic, making the formation of alcohol less favourable. In comparison with benzophenone, a higher yield of carboxylic acid (>30% versus ~15%) was obtained with 4-phenylbenzophenone in all ionic liquids due to the weaker basicity of 4-phenylbenzophenone radical anion.
- Zhao, Shu-Feng,Horne, Mike,Bond, Alan M.,Zhang, Jie
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p. 19247 - 19254
(2015/07/27)
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- Selective reduction of aromatic ketones in aqueous medium mediated by Ti(III)/Mn: A revised mechanism
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An experimental study on the role played by each of the reagents involved in the selective reduction of aromatic ketones in aqueous medium is reported. In this reaction, the reduction of aromatic ketones is mediated by Cp 2TiCl. Moreover, the presence of Mn in the reaction medium is mandatory. To account for these findings, a substantially revised mechanism is proposed.
- Rosales, Antonio,Mu?oz-Bascón, Juan,Roldan-Molina, Esther,Casta?eda, Mayra A.,Padial, Natalia M.,Gans?uer, Andreas,Rodríguez-García, Ignacio,Oltra, J. Enrique
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p. 7672 - 7676
(2014/11/08)
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- Ketyl-type radicals from cyclic and acyclic esters are stabilized by SmI2(H2O)n: the role of SmI2(H 2O)n in post-electron transfer steps
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Mechanistic details pertaining to the SmI2-H2O- mediated reduction and reductive coupling of 6-membered lactones, the first class of simple unactivated carboxylic acid derivatives that had long been thought to lie outside the reducing range of SmI2, have been elucidated. Our results provide new experimental evidence that water enables the productive electron transfer from Sm(II) by stabilization of the radical anion intermediate rather than by solely promoting the first electron transfer as originally proposed. Notably, these studies suggest that all reactions involving the generation of ketyl-type radicals with SmI2 occur under a unified mechanism based on the thermodynamic control of the second electron transfer step, thus providing a blueprint for the development of a broad range of novel chemoselective transformations via open-shell electron pathways.
- Szostak, Michal,Spain, Malcolm,Procter, David J.
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supporting information
p. 8459 - 8466
(2014/06/24)
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- Highly regioselective and chemoselective titanocene mediated Barbier-type allylation reactions
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Titanocene carboxylate 1 is an excellent chemoselective reagent for unprecedented α-regioselective Barbier-type reactions. It constitutes the first titanocene(iii) able to tolerate epoxides and readily reduced carbonyl compounds, such as aromatic and α,β-unsaturated aldehydes. The Royal Society of Chemistry.
- Morcillo, Sara P.,Martinez-Peragon, Angela,Jakoby, Verena,Mota, Antonio J.,Kube, Christian,Justicia, Jose,Cuerva, Juan M.,Gansaeuer, Andreas
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supporting information
p. 2211 - 2213
(2014/02/14)
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- Homogeneous and heterogeneous photoredoxcatalyzed hydroxymethylation of ketones and keto esters: Catalyst screening, chemoselectivity and dilution effects
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The homogeneous titanium- and dye-catalyzed as well as the heterogeneous semiconductor particle-catalyzed photohydroxymethylation of ketones by methanol were investigated in order to evaluate the most active photocatalyst system. Dialkoxytitanium dichlorides are the most efficient species for chemoselective hydroxymethylation of acetophenone as well as other aromatic and aliphatic ketones. Pinacol coupling is the dominant process for semiconductor catalysis and ketone reduction dominates the Ti(OiPr)4/methanol or isopropanol systems. Application of dilution effects on the TiO2 catalysis leads to an increase in hydroxymethylation at the expense of the pinacol coupling.
- Griesbeck, Axel G.,Reckenthaeler, Melissa
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supporting information
p. 1143 - 1150
(2014/06/09)
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- Mg/Triethylammonium formate: A useful system for reductive dimerization of araldehydes into pinacols; Nitroarenes into azoarenes and azoarenes into hydrazoarenes
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Studies are reported which describes the effectiveness of triethylammonium formate in the presence of magnesium for the efficient intermolecular pinacol coupling using MeOH as solvent, Various aromatic carbonyls underwent smooth reductive coupling to give the corresponding I ,2-diols. A series of azo compounds were obtained by the reductive coupling of nitroaromatics while azo compounds were reduced to the corresponding hydrazoarenes by this system. There was no adverse effect on the other reducible and hydrogenolysable groups such as ether linkage, hydroxy and halogens. The reactions are clean, high yielding and inexpensive. All the reactions proceeded smoothly at ambient temperature.
- Pamar, M. Geeta,Govender,Muthusamy,Krause, Ruiw M.,Nanjundaswamy
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p. 969 - 974
(2014/03/21)
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- Reductive coupling of aromatic aldehydes and acetophenone induced by TiCl4-Al/CH2(COOEt)2
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Induced by TiCl4-Al/CH2(COOEt)2 in CH 2Cl2, some aromatic aldehydes and acetophenone can afford the corresponding 1,2-diols in 13-91 % yields with good dl- diastereoselectivities within 45-60 min at room temperature.
- Song, Chang-Ying,Wang, Shu-Xiang,Chu, Wen-Hao,Li, Ji-Tai,Zhou, Zheng,Li, Hong-Yu,Cao, Zi-Qing
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p. 7993 - 7996
(2013/09/23)
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- Photoaddition reactions of acetylpyridines with silyl ketene acetals: SET vs [2 + 2]-cycloaddition pathways
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Photoaddition reactions of silyl ketene acetals with 2-, 3- and 4-acetylpyridine have been explored. The results show that the acetylpyridines react with an electron rich, dimethyl-substituted silyl ketene acetal via a pathway in which excited state singl
- Cho, Dae Won,Park, Hea Jung,Yoon, Ung Chan,Lee, Hyang-Yeol,Mariano, Patrick S.
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p. 10304 - 10313
(2013/01/15)
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- Cerium metal-mediated Reformatsky-type reaction with ethyl bromosuccinate for the synthesis of novel paraconic acid analogs
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The treatment of cerium metal with ethyl bromosuccinate (1) forms the stabilized organolanthanoid intermediate (2), which reacts with carbonyl compounds in a Reformatsky-type reaction, under mild conditions, to produce functionalized γ-substituted paraconic acids (4) in good yields.
- Rodrigues, Shirley M. M.,Nardini, Viviani,Constantino, Mauricio G.,Da Silva, Gil Valdo J.
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supporting information
p. 6136 - 6137,2
(2020/08/20)
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- A flexible enantioselective approach to 3,4-dihydroxyprolinol derivatives by SmI2-mediated reductive coupling of chiral nitrone with ketones/aldehydes
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A flexible enantioselective approach to polyhydroxylated prolinol derivatives was described, which is based on the samarium diiodide-mediated reductive coupling of the chiral nitrone (3S,4R)-8, derived from d-isoascorbic acid with aldehydes/ketones. Thereby, polyhydroxyprolinol derivatives 9a-e and 9h-j were obtained from aromatic ketones and aliphatic aldehydes in good to excellent yields of 65-91%. These reductive hydroxyalkylations are highly diastereoselective in establishing the C-4 stereogenic center. By this way, the asymmetric syntheses of (-)-8a-epi-swainsonine (4) and (-)-8,8a-di-epi- swainsonine (5) have been achieved.
- Zhang, Hong-Kui,Xu, Shou-Qiang,Zhuang, Jia-Jia,Ye, Jian-Liang,Huang, Pei-Qiang
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experimental part
p. 6656 - 6664
(2012/08/29)
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- Visible light mediated homo- and heterocoupling of benzyl alcohols and benzyl amines on polycrystalline cadmium sulfide
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The oxidative coupling of sp3 hybridized carbon atoms by photocatalysis is a valuable synthetic method as stoichiometric oxidation reagents can be avoided and dihydrogen is the only byproduct of the reaction. Cadmium sulfide, a readily available semiconductor, was used as a visible light heterogeneous photocatalyst for the oxidative coupling of benzyl alcohols and benzyl amines by irradiation with blue light. Depending on the structure of the starting material, good to excellent yields of homocoupling products were obtained as mixtures of diastereomers. Cross-coupling between benzyl alcohols and benzyl amines gave product mixtures, but was selective for the coupling of tetrahydroisoquinolines to nitromethane. The results demonstrate that CdS is a suitable visible light photocatalyst for oxidative bond formation under anaerobic conditions.
- Mitkina, Tatiana,Stanglmair, Christoph,Setzer, Wolfgang,Gruber, Michael,Kisch, Horst,Koenig, Burkhard
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supporting information; experimental part
p. 3556 - 3561
(2012/06/01)
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- Selective solar photocatalytic oxidation of ethylbenzene on C, N, and S doped TiO2
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The liquid-phase photo-oxidation of ethylbenzene (EB) is investigated in solar light with air/O2/N2 at atmospheric pressure, in a batch reactor using acetonitrile medium. It is carried out over TiO2 doped with C, N, and S
- Srinivas, Basavaraju,Anil Kumar Reddy, Police,Rajesh, Mucharla,Durga Kumari, Valluri,Subrahmanyam, MacHiraju,De, Bhudev Ranjan
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experimental part
p. 901 - 918
(2012/05/20)
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- Polymer-mediated pinacol rearrangements
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Both poly(3,4-ethylenedioxythiophene) and poly(pyrrole) mediate a pinacol rearrangement of 1,2-diols. The yields of ketone or aldehyde products are comparable to those observed for treatment with mineral acids or Lewis acids. The advantage of this protocol is a two-phase reaction medium in hydrocarbon solvents that allows facile recovery of the products by simple filtration of the polymer and removal of solvents. Both the polymer and the hydrocarbon solvent may be recovered and used in subsequent reactions. Georg Thieme Verlag Stuttgart · New York.
- Pavlik, Christopher,Morton, Martha D.,Smith, Michael B.
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experimental part
p. 2191 - 2194
(2011/11/06)
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- Zn-AlCl3 · 6H2O-mediated reaction in aqueous media: Pinacol coupling reaction
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(Chemical Equation Presented) Vicinal diols have been prepared in good yield by pinacol coupling reaction of aromatic aldehydes and ketones with commercially available zinc and AlCl3 · 6H2O in water. Copyright Taylor & Francis Group, LLC.
- Hazarika, Binod Kumar,Dutta, Dilip Kumar
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experimental part
p. 1088 - 1093
(2011/04/25)
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- Selective reductions of the carbonyl compounds and aryl halides with Ni-Al alloy in aqueous alkali medium
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The carbonyl compounds and the aryl halides are efficiently reduced by Ni-Al alloy powder, in aqueous alkali medium, with or without organic solvents. The relative reactivities in a series of structurally selected reducible compounds showed a sequence of reactivity in agreement with the mechanism involving a direct electron transfer from aluminum to the organic phase. In some cases an important change in reactivity with respect to conversion of the reducing reagent was notified. Most probably this complicated variability is the result of the changes in composition and morphology of the reacting Ni-Al alloy.
- Suceveanu, Mirela,Raicopol, Matei,Enache, Raluca,Finaru, Adriana,Rosca, Sorin I.
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experimental part
p. 690 - 695
(2012/06/04)
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- A unique proton coupled electron transfer pathway for electrochemical reduction of acetophenone in the ionic liquid [BMIM][BF4] under a carbon dioxide atmosphere
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The mechanism of electrochemical reduction of acetophenone in 1-butyl-3-methylimidazolium tetrafluroborate ([BMIM][BF4]) under nitrogen (N2) and carbon dioxide (CO2) atmospheres have been investigated using transient voltammetry, steady-state voltammetry, bulk electrolysis and numerical simulation. Under a N2 atmosphere, acetophenone undergoes a one-electron reduction to the radical anion followed by rapid dimerization reactions with an apparent rate constant of 1.0 × 106 M-1 s-1. In contrast, under a CO 2 atmosphere, the electrochemical reduction of acetophenone is an overall two-electron transfer chemically irreversible process with the final electrolysis product being 1-phenylethanol, instead of the anticipated 2-hydroxy-2-phenylpropionic acid resulting from an electrocarboxylation reaction. A proton coupled electron transfer pathway leading to the formation of 1-phenylethanol requires the presence of a sufficiently strong proton donor which is not available in neat [BMIM][BF4]. However, the presence of CO2 enhances the C-2 hydrogen donating ability of [BMIM]+ due to strong complex formation between the deprotonated form of [BMIM] +, N-heterocyclic carbene, and CO2, resulting in a thermodynamically favorable proton coupled electron transfer pathway.
- Zhao, Shu-Feng,Wu, La-Xia,Wang, Huan,Lu, Jia-Xing,Bond, Alan M.,Zhang, Jie
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experimental part
p. 3461 - 3468
(2012/02/02)
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- Electrocatalytic carboxylation of aromatic ketones with carbon dioxide in ionic liquid 1-butyl-3-methylimidazoliumtetrafluoborate to α-hydroxy- carboxylic acid methyl ester
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A new electrochemical procedure for the electrocatalytic carboxylation of aromatic ketones with carbon dioxide in ionic liquid, 1-butyl-3- methylimidazolium tetrafluoborate (BMIMBF4), to α- hydroxycarboxylic acid methyl ester was investigated for the first time. The electrochemical behavior of acetophenone in BMIMBF4 was studied by cyclic voltammetry with a reduction peak at -1.9 V (vs. Ag). The electrolyses experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, followed by addition of an alkylating agent, affording the α-hydroxycarboxylic acid methyl ester in a moderate yield (62%). The results showed that the yields were strongly affected by various factors: temperature, current density, charge passed, electrode material and substrate concentration. Moreover, the ionic liquid was successfully recycled for this reaction.
- Feng, Qiuju,Huang, Kelong,Liu, Suqin,Yu, Jingang,Liu, Fangfei
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experimental part
p. 5137 - 5141
(2011/06/27)
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- Iron-catalyzed pinacol coupling of aryl ketones with a phenyltitanium reagent: A new type of catalytic reaction
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A reaction of aryl ketones with phenyltitanium triisopropoxide ([PhTi(Oi-Pr)3]) in the presence of [Fe(acac)3] as a catalyst (1 mol%) gave the corresponding pinacols in high yields. The catalytic cycle of this process involves an iron-catalyzed disproportionation of [PhTi(Oi-Pr) 3] into biphenyl and a lowvalent titanium species.
- Hayashi, Tamio,Sasaki, Keigo
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scheme or table
p. 492 - 494
(2011/06/25)
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- An efficient photoinduced deprotection of aromatic acetals and ketals
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A novel type of photodeprotection reaction of simple aromatic acetals and ketals is described. The deprotection is highly efficient under optimized conditions. The aromatic ring confers the photoreactivity to the compounds. The efficiency of the process depends on the structure of the acetal moiety. The common minor side reaction, the photooxidation, becomes the major reaction pathway in the cases of cyclic acetals. The use of photon as only reagent makes this procedure especially attractive for acetal deprotection.
- Thevenet, Damien,Neier, Reinhard
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scheme or table
p. 331 - 346
(2011/04/22)
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- Characterization of free radical spin adducts of 5-diisopropyloxy- phosphoryl5-methyl-1-pyrroline-A/-oxide using mass spectrometry and 31P nuclear magnetic resonance
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5-Diisopropyloxy-phosphoryl-5-methyl-1-pyrroline-N-oxide;(DIPPMPO) was used to trap a variety of free radicals and the stable compounds generated by the natural decomposition of the initially formed spin adducts were characterized by 31P nuclear magnetic resonance (NMR) and mass spectrometry. Initially, the starting spin trap DIPPMPO was completely characterized using GC-MS and its fragmentation pathway was studied in detail. Then, DIPPMPO was used to trap an oxygen-centered free radical (the hydroxyl radical 'OH) and two carbon-centered free radicals (methyl CH3 and 1-phenyl-ethanol-1-yl CCH3(OH)Ph radicals). The 31P NMR signals were thus assigned and the structures of adducts were studied and confirmed by mass spectrometry. Overall, the fragmentation pathways of the radical adducts proceed mainly via the loss of the diisopropyloxy(oxido)phosphoranyl radical. For the specific case of trapping-OH radicals, it is possible to visualize the rearrangement of the nitroxide radical adduct to its nitrone form as invoked in the literature. This spin trapping technique, coupled with 31P NMR and MS, provides a tool for the identification of short-lived and low molecular weight free radicals present in a variety of processes. IM Publications LLP 2010 All rights reserved.
- Zoia, Luca,Argyropoulos, Dimitris S.
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experimental part
p. 175 - 185
(2011/01/12)
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- Praseodymium-induced pinacol formation
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In an attempt to regenerate Ti(0) from TiOx for possible application in a catalytic McMurry coupling reaction, a praseodymium-based pinacol reaction was uncovered. This reaction formed the two products 2,3-diphenyl-2,3-butanediol (3) and α,β-dimethyl-α-phenyl-β-[(trimethylsilyl)oxy]- benzene-ethanol (6) in a 1:3 ratio. Copyright Taylor & Francis Group, LLC.
- Drapo, Jeanette R.,Priefer, Ronny
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experimental part
p. 85 - 92
(2009/04/07)
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- Salt/ligand-activated low-valent titanium formulations: the 'salt effect' on diastereoselective carbon-carbon bond forming SET reactions
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A comprehensive study on the influence of exogenously added electropositive metal salts as promoters/secondary activators on preformed LVT species has resulted in the construction of highly efficient low-valent titanium (LVT) reagents. These salt-activated LVT reagents while exhibiting enhanced chemoselectivity and diastereoselectivity accelerated the reductive olefination rates of aromatic and aliphatic carbonyls under ambient temperature conditions and in much reduced reaction times. The versatility of the salted reagent was further explored in other single electron transfer reactions, namely, imino-pinacol couplings and one-pot synthesis of phenanthrenes from o-alkoxy aromatic carbonyls. We envisage that, in contrast to multiphase heterogeneous colloidal slurries, salt-activated LVT reagents afforded uniformly viscous homogeneous slurries generating a highly reactive monomeric intermetallic LVT complex. Continued judicious exploration of the emerging paradigms by studying the influence of external ligands/auxiliaries/redox agents on LVT reagents, and organometallics in general, will be critical to widen the scope and utility of the classical McMurry reaction and other SET reactions.
- Rele, Shyam M.,Nayak, Sandip K.,Chattopadhyay, Subrata
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p. 7225 - 7233
(2008/12/20)
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- Zirconocene dichloride-catalyzed pinacol coupling of aromatic aldehydes and ketones
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The reductive coupling of aromatic aldehydes and ketones has been achieved using a catalytic amount of zirconocene dichloride in the presence of magnesium metal and chlorotrimethylsilane in THF at room temperature to afford the corresponding 1,2-diols in good yields and diastereoselectivity. Copyright Taylor & Francis Group, LLC.
- Lakshmi Kantam,Aziz, Khathija,Likhar, Pravin R.
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p. 1437 - 1445
(2007/10/03)
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- Samarium-induced convenient reductive dimerization of aromatic ketones in aqueous methanol: A mechanistic approach
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Samarium metal has been used for the reductive dimerization of aromatic ketones in the presence of additives; the most probable mechanism has been advanced to explain the diastereoselectivity of this dimerization reaction.
- Banik, Bimal K.,Banik, Indrani,Aounallah, Nacer,Castillo, Mark
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p. 7065 - 7068
(2007/10/03)
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- Samarium/N-bromosuccinimide-induced reductive dimerization of carbonyl compounds
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Stereoselective reductive coupling of carbonyl compounds has been achieved using samarium/N-bromosuccinimide in methanol. The combination of these agents has proved a powerful addition to the arsenal of samarium-based reductants currently utilized.
- Banik, Bimal K.,Banik, Indrani,Samajdar, Susanta,Cuellar, Rogelio
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p. 2319 - 2322
(2007/10/03)
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- Pinacol coupling of aromatic aldehydes mediated by TiCl3-Mn-EtOH under ultrasound irradiation
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Pinacol coupling of aromatic aldehydes and ketones by TiCl 3-Mn-EtOH under ultrasound irradiation can lead to the corresponding pinacols in 16-86% yields at room temperature.
- Li, Ji-Tai,Chen, Yan-Xue,Chang, Rui-Xiang,Li, Tong-Shuang
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p. 784 - 786
(2007/10/03)
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- Novel and efficient Ni-mediated pinacol coupling of carbonyl compounds
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It was firstly found that the Rieke Ni generated in situ was able to promote the pinacol coupling of various carbonyls efficiently. Based on this information, another catalytically effective, cheaper and more convenient NiCl2(Cat.)/Mg/TMSCl system was designed and developed further successfully. The interesting single-electron transfer (SET) mechanisms for the coupling reactions were proposed. Additionally, the DL/meso diastereoselectivity and some additive effects were also explained in terms of the proposed mechanisms.
- Shi, Lei,Fan, Chun-An,Tu, Yong-Qiang,Wang, Min,Zhang, Fu-Min
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p. 2851 - 2855
(2007/10/03)
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- Development of a catalytic electron transfer system mediated by transition metal ate complexes: Applicability and tunability of electron-releasing potential for organic transformations
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We have developed a catalytic electron transfer (ET) system composed of a transition metal ate complex (Me3M(II)Li; M = Co(II), Mn(II), Fe(II)) and magnesium. This system (catalytic Me3M(II)Li/Mg) turned out to be effective for various ET reactions, such as the desulfonylation of N-phenylsulfonyl amides, and others (the chemoselective cleavage of O-allyl groups, the reduction of nitro groups, the partial reduction of diketones, and the reductive coupling of diphenyliodonium salt). The ET ability of this system can be tuned by changing the ligands of the ate complexes. This tunability was experimentally and electrochemically demonstrated: alkoxy-ligated and dianion-type ET ate complexes showed attenuated and enhanced reducing abilities, respectively. The modification of the ET abilities was evaluated by means of electrochemical measurements and chemical reactions. These results provide a basis for the design of various tailor-made ET ate complexes.
- Uchiyama, Masanobu,Matsumoto, Yotaro,Nakamura, Shinji,Ohwada, Tomohiko,Kobayashi, Nagao,Yamashita, Natsuno,Matsumiya, Atsushi,Sakamoto, Takao
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p. 8755 - 8759
(2007/10/03)
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- Samarium(II)-mediated pinacol coupling in water: Occurrence of unexpected disproportionation and action of low-valent samarium as an active species
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(Matrix presented) Mechanistic studies of one-electron reduction in water using samarium were carried out. Unexpected disproportionation in water was observed via UV-vis spectroscopic analysis. This fact indicates that low-valent samarium species can exist in water. Furthermore, the SmCl3-Sm and SmCl3-Mg systems were found to act as good one-electron reducing agents in water.
- Matsukawa, Satoru,Hinakubo, Yumi
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p. 1221 - 1223
(2007/10/03)
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- CeCl3/Sm promoted pinacolic coupling of aromatic aldehydes and ketones
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The pinacolic coupling of aromatic aldehydes and ketone was performed with cerium trichloride and samarium in THF at room temperature to afford the corresponding 1,2-diols in good yields.
- Li, Xue,Zhang, Songlin,Zhang, Xinying,Wang, Xiao Yang
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p. 1043 - 1045
(2007/10/03)
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- Some uses of mischmetall in organic synthesis
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Mischmetall, an alloy of the light lanthanides, has been used in a variety of organic reactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacolic coupling reactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been explored in Imamoto and Luche-Fukuzawa reactions and in Mukaiyama aldol reactions.
- Lannou, Marie-Isabelle,Hélion, Florence,Namy, Jean-Louis
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p. 10551 - 10565
(2007/10/03)
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- Titanocene-catalysed, selective reduction of ketones in aqueous media. A safe, mild, inexpensive procedure for the synthesis of secondary alcohols via radical chemistry
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We report here a novel procedure for the reduction of ketones to secondary alcohols using catalytic quantities of commercially available Cp2TiCl2, inexpensive Zn dust and water as proton source. Mechanistically the reaction presumably proceeds via titanoxy radicals. In practice this reduction process has significant advantages: it shows an interesting selectivity pattern, takes place under mild conditions using safe, cheap reagents and does not require anhydrous solvents. The proton-donor activity of water under these conditions avoids the use of the frequently poisonous hydrogen-atom donors generally required to reduce free radicals. This procedure is also highly convenient for synthesising deuterium-labelled alcohols employing relatively inexpensive D2O as deuterium source.
- Barrero, Alejandro F.,Rosales, Antonio,Cuerva, Juan M.,Gans?uer, Andreas,Oltra, J. Enrique
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p. 1079 - 1082
(2007/10/03)
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