- Visible-Light Induced Photofixation of CO2 into Benzophenone Catalyzed by Colloidal CdS Microcrystallites
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Photocatalytic fixation of CO2 into benzophenone has been achieved under λ > 400-nm light irradiation of a CO2-saturated DMF solution of colloidal CdS microcrystallites as photocatalysts, triethylamine as a sacrificial electron donor, and benzophenone yielding benzilic acid with benzhydrol and benzopinacol.
- Kanemoto, Masashi,Ankyu, Hirofumi,Wada, Yuji,Yanagida, Shozo
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- Chemical reactions of benzophenone photoirradiated in 1,2-polybutadiene
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The photolysis of benzophenone (BP) in 1,2-polybutadiene (1,2PB) was studied at low radiation intensity in order to clarify some aspects of BP photochemistry and of 1,2PB photocrosslinking. The expected primary photoreactions of hydrogen abstraction and c
- Barboiu, Virgil,Avadanei, Mihaela Iuliana
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- Interaction between alkali metal aromatic ketone radical anions and the chlorides of lithium and magnesium in solution. A case of a carbon-carbon bond strengthening through complex formation
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The interaction between lithium, sodium and potassium salts with the pre-formed radical anions of benzophenone, 2-methylbenzophenone, 2,4,6-trimethylbenzophenone or fluorenone, and lithium or magnesium chlorides has been studied by nuclear magnetic resona
- Micha-Screttas, Maria,Heropoulos, Georgios A.,Steele, Barry R.
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- Rate-Determining Step of the Reactions of Benzophenone with Various Grignard Reagents
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Carbonyl carbon kinetic isotope effects (KIEs) have been determined for the reaction of benzophenone-7-(14)C with various Grignard reagents at 0 deg C.The observed KIEs are as follows: MeMgI/Et2O, 12k/14k = 1.056 +/- 0.002; MeMgBr/Et2O, 1.050 +/- 0.011; MeMgBr/THF, 1.056 +/- 0.004; PhMgBr/Et2O, 1.056 +/- 0.004; o-CH3C6H4MgBr/Et2O, 1.060 +/- 0.014; CH2=CHCH2MgBr/Et2O, 0.999 +/- 0.003; CH3CH=CHCH2MgBr/Et2O, 0.999 +/- 0.002; PhCH2MgBr/Et2O, 1.024 +/- 0.007; t-BuMgCl/Et2O, 1.010 +/- 0.007, 1.004 +/- 0.004; MeMgI + 5 mol percent FeCl3/Et2O, 1.063 +/- 0.033 (for 1,2-adduct formation), 0.997 +/- 0.019 (for pinacol formation).The relative reactivities of ortho-, meta-, and para-substituted benzophenones with these reagents were also determined by competition experiments.The reactions can be classified into three groups on the basis of these results: the first group gives a large (14)C KIE, a medium-sized Hammett ρ value, and a large steric rate retardation due to ortho substituents; the second gives a KIE of unity, a near-zero ρ value, and no steric rate retardation; and the third gives a small (14)C KIE, a large ρ value, and no steric rate retardation.It was concluded that the intimate mechanism of these Grignard reactions is diffrent although they all follow the single-electron-transfer (SET) scheme; specifically, the rate-determining step for MeMgX, ArMgBr, and PhCH2MgBr is C-C bond formation while that for allylic reagents is initial SET.The rate-determining step for t-BuMgCl is the isomerization of the radical ion pair intermediate.
- Yamataka, Hiroshi,Matsuyama, Toyoki,Hanafusa, Terukiyo
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- Reduction of Crystal Violet by Diphenylketyl Radicals
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Crystal violet (CV+) is stable to direct photolysis in acetonitrile at λirr >/= 366 nm even in the presence of hydrogen donors (benzhydrol and 2-propanol).However, when benzophenone (K) is present in samples containing hydrogen donor and λirr + by diphenylketyl (KH.) followed by hydrogen transfer to the intermediate CV. with formation of the leuco dye (CVH) is proposed.The rate constant (k6) for the electron transfer reaction CV+ + KH. -> CV. + K + H+, k6 = 6 +/- 2 x 105 M-1 s-1 (6) has been determined by two methods both of which rely on the competition between reactions 5 and 6 2KH. -> K2H2, k5 = 1.05 +/- 0.02 x 108 M-1 s-1 (5) In the first the quantum yield of sensitized fading is determined as a function of CV+ concentration.In the second the rates of benzpinacol formation in the absence and presence of CV+ are followed.
- Naguib, Yousry M. A.,Cohen, Saul G.,Steel, Colin
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- Visible-light Induced Photocatalytic Fixation of CO2 into Benzophenone Using Poly(p-phenylene) as a Photocatalyst
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Photoreductive fixation of CO2 into benzophenone can be achieved in a CO2-saturated DMF solution by using poly(p-phenylene) as a heterogeneous photocatalyst and triethylamine as an electron donor.The presence of quaternary ammonium salts increases the yield of benzylic acid as a CO2-photofixed product from benzophenone.
- Ogata, Tomoyuki,Hiranaga, Kunizo,Matsuoka, Shinjiro,Wada, Yuji,Yanagida, Shozo
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- EFFECT OF THE SOLVENT ON REDUCTION OF AZOMETHINE DYES WITH KETYL RADICALS AND RECOMBINATION OF KETYL RADICALS
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The rate constants of transfer of a hydrogen atom from ketyl radicals to azomethine dyes (kH) and the rate constants of recombination of ketyl radicals (2kr) in different solvents were measured by the method of pulsed photolysis.The dependences of kH and 2kr on the polarity of the solvent are V-shaped: kH and 2kr are maximum in weakly solvating solvents and in water and are minimum in nucleophilic solvents of medium polarity.This is due to the fact that nucleophilic solvation decreases and electrophilic solvation increases the reactivity of the ketyl radicals.
- Tatikolov, A. S.,Sklyarenko, V. I.,Kuz'min, V. A.,Al'perovich, M. A.
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- Photochemical Cycloaddition of Benzophenone to 7-Methylenetetracyclo2,8.04,6>octan-3-one and its Alcohol Derivative
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Irradiation of benzophenone with 2,4-dimethyl- or 1,2,4-trimethyl-7-methylenetetracyclo2,8.04,6>octan-3-one affords oxetans (3a) and (3b), respectively, while irradiation with the alcohol derivative (2) affords a rearranged product (5) in addition to an oxetan.
- Nitta, Makoto,Kuroki, Toshio,Sugiyama, Hiroshi
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- Visible light-induced photofixation of CO2 into benzophenone: Roles of poly(p-phenylene) as photocatalyst and two-electron mediator in the presence of quaternary onium salts
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Visible light-induced photocatalytic fixation of CO2 into benzophenone (1) has been carried out in CO2-saturated DMF (N,N-dimethylformamide) using poly(p-phenylene) (PPP) as a heterogeneous photocatalyst and triethylamine as an electron donor. Diphenylglycolic acid (2) is produced as a CO2-fixed product together with benzhydrol (3), benzopinacol (4) and 1,1-diphenylpropane-1,2-diol (5). The presence of quaternary onium salts such as tetraethylammonium chloride (Et4NCl) increases the yield of 2 in the presence of CO2 and those of 3 and 5 in the absence of CO2. The soft onium cations from quaternary onium salts are proposed to stabilize diphenylcarbinol anion (9) as a common precursor of 2, 3 and 5 on the basis of the HSAB concept. Further, the enhanced formation of PPP dianions (7) through PPP radical anions (6) has been examined in the reduction of PPP with sodium metal in the presence of Et4NCl. Photocatalysis of PPP in the CO2 fixation is discussed in terms of onium salt effects and favorable photoformation of 6 and 7 as an electron pool in the presence of quaternary onium cations.
- Wada, Yuji,Ogata, Tomoyuki,Hiranaga, Kunizo,Yasuda, Hiroyuki,Kitamura, Takayuki,Murakoshi, Kei,Yanagida, Shozo
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- Ultrasound effects on the photopinacolization of benzophenone
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Ultrasonic irradiation is able to modify the course of several photochemical reactions, especially bimolecular, proceeding via triplet states. These effects were illustrated in the study of benzophenone photopinacolization in ethanol. The rates and yields increase when sonication is applied simultaneously to UV irradiation. An explanation is based on a 2-fold effect: (i) light-absorbing transient species undergo sonolytic decomposition, making the photoconversion more efficient, and (ii) sonication induces the triplet state quenching, as shown by Stern-Volmer plots from experiments run in the presence of naphthalene, probably due to the easier collisional deactivation processes favored by the homogeneous distribution of the activated species.
- Gaplovsky,Gaplovsky,Toma,Luche
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- Visible-Light Induced Photocatalysis of Partially Fluorinated Poly(p-phenylene) and Related Linear Phenylene Derivatives
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As a partially fluorinated poly(p-phenylene) derivative, yellow powder PF-PPP-n with high solubility in organic solvents was prepared as a mixture of oligomers by nickel-catalyzed polycondensation of the Grignard reagent from 1-bromo-2,4,6-trifluorobenzene.PF-PPP-n shows photocatalytic activity for reduction of water to H2, carbonyl compounds to alcohols, and dimethyl maleate and fumarate to the succinate under visible-light (λ > 400 nm) irradiation in the presence of triethylamine as a sacrificial electron donor.The photocatalysis was compared with those of other related fluorinated linear aromatics such as perfluorinated poly(p-phenylene sulfide) (F-PPS-n), perfluorinated poly(p-phenylene) (F-PPP-n).Their spectral characteristics and photocatalysis are discussed on the basis of the semiempirical molecular orbital calculations.
- Maruo, Katsuyo,Yamada, Kazuyori,Wada, Yuji,Yanagida, Shozo
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- Role of TiO2-based photocatalysts on the synthesis of the pharmaceutical precursor benzhydrol by UVA-LED radiation
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The influence of several reactional parameters was investigated on the photocatalytic reduction of benzophenone to the pharmaceutical precursor benzhydrol under UVA-LED radiation. The optical semiconductor titanium dioxide was loaded with 1.0 wt.% of nobl
- Lopes, Joana C.,Sampaio, Maria J.,Rosa, Bernardo,Lima, Maria J.,Faria, Joaquim L.,Silva, Cláudia G.
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- Site-selective D2O-mediated deuteration of diaryl alcoholsviaquantum dots photocatalysis
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Owing to the high synthetic value of deuteration in the pharmaceutical industry, we describe herein the conversion of a range of aromatic ketones to deuterium-labeled products in good to excellent yields. Efficient and site-selective deuteration of benzyl alcohols by D2O with visible light irradiation of quantum dots (QDs), together with gram-scale synthesis and photocatalyst recycling experiments indicated the potential of the developed method in practical organic synthesis.
- Li, Xu-Bing,Nan, Xiao-Lei,Tung, Chen-Ho,Wang, Yao,Wu, Li-Zhu
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p. 6768 - 6771
(2021/07/13)
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- Tunable System for Electrochemical Reduction of Ketones and Phthalimides
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Herein, we report an efficient, tunable system for electrochemical reduction of ketones and phthalimides at room temperature without the need for stoichiometric external reductants. By utilizing NaN3 as the electrolyte and graphite felt as both the cathode and the anode, we were able to selectively reduce the carbonyl groups of the substrates to alcohols, pinacols, or methylene groups by judiciously choosing the solvent and an acidic additive. The reaction conditions were compatible with a diverse array of functional groups, and phthalimides could undergo one-pot reductive cyclization to afford products with indolizidine scaffolds. Mechanistic studies showed that the reactions involved electron, proton, and hydrogen atom transfers. Importantly, an N3/HN3 cycle operated as a hydrogen atom shuttle, which was critical for reduction of the carbonyl groups to methylene groups.
- Chen, Gong,Qiao, Tianjiao,Wang, Yaxin,Zhang, Jian,Zhao, Jianyou
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p. 3297 - 3302
(2021/10/14)
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- Enhanced catalytic activity of one-dimensional CdS @TiO2 core-shell nanocomposites for selective organic transformations under visible LED irradiation
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In this study, we are interested in the photocatalytic activity under visible LED irradiation of one- dimensional (1D) CdS @TiO2 core–shell nanocomposites (CSNs) prepared through a facile and convenient method. For the synthesis of 1D CdS@TiO2 core/shell structure, titania source (Tetrabutyl titanate) was hydrolyzed by water vapor transmission on the surface of CdS nanowires (NWs) which were prepared via solvothermal method. The characterization of 1D CdS@TiO2 core–shell nanocomposites (CdS@TiO2 CSNs) was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, and UV–Vis diffuse reflectance spectroscopy (DRS). The as-synthesized sample was utilized for the selective reduction of nitro compounds to benzimidazole and anilide, and also the reduction of benzophenones to alcohol under blue LED irradiation. The 1D CdS@TiO2 CSNs exhibited enhanced photoactivity compared with the pure TiO2, CdS nanowires and commercial TiO2-P25. The excellent reusability of the photocatalyst was examined for six runs. The results demonstrated that the prepared sample has the potential to provide a promising visible light-driven photocatalyst for other organic transformations.
- Eskandari, Parvin,Kazemi, Foad,Ramdar, Moosa,Zand, Zahra
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- Photodriven Dehydrogenative Homocoupling of Benzylic C-H Bonds Forming Strained C-C Bonds
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A photoinduced dehydrogenative homocoupling reaction of alkylarenes is reported. Gaseous hydrogen is evolved as the sole byproduct and neither oxidants nor hydrogen acceptors are required. The present reaction offers an environmentally benign and atom-economical means for forming sterically strained C-C single bonds. It also gives a remarkable example of photodriven reactions overcoming a considerable rise in energy.
- Ishida, Naoki,Son, Mingon,Kawasaki, Tairin,Ito, Misato,Murakami, Masahiro
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supporting information
p. 2067 - 2070
(2021/10/14)
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- 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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- Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots
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We present an efficient and versatile visible light-driven methodology to transform aryl aldehydes and ketones chemoselectively either to alcohols or to pinacol products with CdSe/CdS core/shell quantum dots as photocatalysts. Thiophenols were used as proton and hydrogen atom donors and as hole traps for the excited quantum dots (QDs) in these reactions. The two products can be switched from one to the other simply by changing the amount of thiophenol in the reaction system. The core/shell QD catalysts are highly efficient with a turn over number (TON) larger than 4 × 104 and 4 × 105 for the reduction to alcohol and pinacol formation, respectively, and are very stable so that they can be recycled for at least 10 times in the reactions without significant loss of catalytic activity. The additional advantages of this method include good functional group tolerance, mild reaction conditions, the allowance of selectively reducing aldehydes in the presence of ketones, and easiness for large scale reactions. Reaction mechanisms were studied by quenching experiments and a radical capture experiment, and the reasons for the switchover of the reaction pathways upon the change of reaction conditions are provided.
- Xi, Zi-Wei,Yang, Lei,Wang, Dan-Yan,Feng, Chuan-Wei,Qin, Yufeng,Shen, Yong-Miao,Pu, Chaodan,Peng, Xiaogang
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p. 2474 - 2488
(2021/02/05)
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- CBZ6 as a Recyclable Organic Photoreductant for Pinacol Coupling
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A recyclable organic photoreductant (1 mol % CBZ6)-catalyzed reductive (pinacol) coupling of aldehydes, ketones, and imines has been developed. Irradiated by purple light (407 nm) using triethylamine as an electron donor, a variety of 1,2-diols and 1,2-diamines could be prepared. The oxidation potential of the excited state of CBZ6 is established as -1.92 V (vs saturated calomel electrode (SCE)). The relative high reductive potential enables the reductive coupling of carbonyl compounds and their derivatives. CBZ6 can be prepared in gram scale and is acid/base- or air-stable. It could be applied in large-scale photoreductive synthesis and recovered in high yield after the reaction.
- Wang, Hua,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 2900 - 2903
(2021/05/05)
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- 3-Benzoylquinoxalinone as a photoaffinity labelling derivative with fluorogenic properties allowing reaction monitoring under “no-wash” conditions
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Described herein is a quinoxalinone-based photoaffinity probe with caged fluorescence properties. Upon visible blue LED irradiation (λmax450 nm), this photo-crosslinker is able to covalently capture proteins with concomitant fluorescence labelling. This process enables monitoring applications under “no wash” conditions.
- Cauwel, Madeleine,Cosette, Pascal,Galas, Ludovic,Renard, Pierre-Yves,Sabot, Cyrille,Schapman, Damien,Bénard, Magalie,Guillou, Clément,Renault, Kévin
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supporting information
p. 3893 - 3896
(2021/04/26)
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- Oxidative and Redox-Neutral Approaches to Symmetrical Diamines and Diols by Single Electron Transfer/Hydrogen Atom Transfer Synergistic Catalysis
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Homocoupling reactions of benzylamines and benzyl alcohols were examined under synergistic catalysis conditions with a photoredox catalyst and thiobenzoic acid as a hydrogen atom abstractor. When pivalaldehyde was used as an electron acceptor, oxidative dimerization proceeded selectively, whereas the use of benzaldehydes or iminium ions as electron acceptors resulted in redox-neutral coupling. These reactions afforded symmetrical 1,2-diamines and 1,2-diols in good yields.
- Fujita, Masashi,Kobayashi, Fumihisa,Ide, Takafumi,Egami, Hiromichi,Hamashima, Yoshitaka
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supporting information
p. 7151 - 7155
(2020/12/01)
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- GaN nanowires as a reusable photoredox catalyst for radical coupling of carbonyl under blacklight irradiation
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Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III-V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer. This journal is
- Botton, Gianluigi,Cen, Yunen,Cheng, Shaobo,Li, Chao-Jun,Liu, Mingxin,Mi, Zetian,Rashid, Roksana T.,Tan, Lida
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p. 7864 - 7870
(2020/08/19)
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- Crystal-to-Crystal Synthesis of Photocatalytic Metal–Organic Frameworks for Visible-Light Reductive Coupling and Mechanistic Investigations
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Postmodification of reticular materials with well-defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal–organic frameworks (MOFs) to exploit the potential of crystal-to-crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF-520-PC1 and MOF-520-PC2, are straightforwardly obtained by the postfunctionalization of MOF-520 with perylene-3-carboxylic acid (PC1) and perylene-3-butyric acid (PC2). The single crystal-to-crystal transformation yielded the X-ray diffraction structure of catalytic MOF-520-PC2. The well-defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady-state, time-resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF-520-PC2 can be applied for synthesizing gram-scale quantities of products in continuous-flow conditions under steady-state light irradiation. This work provides an alternative approach for the construction of well-defined, metal-free, MOF-based catalysts.
- Bucci, Alberto,Escudero-Adán, Eduardo C.,Gutiérrez, Luis,Kandoth, Noufal,Lloret-Fillol, Julio,Mondal, Suvendu Sekhar,Shafir, Alexandr
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- Practical Method for Reductive Deuteration of Ketones with Magnesium and D2O
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α-Deuterated alcohols have important applications in pharmaceuticals and mechanism studies. Here, we report a new and practical strategy for the reductive deuteration of ketones using a Mg/BrCH2CH2Br/D2O system, which affords α-deuterated alcohols in good yields and with almost quantitative incorporation of deuterium. The synthetic value of this method has been demonstrated by the easy access to deuterated drugs or drug derivatives. This method may inspire the discovery of other deuterium-containing drugs.
- Bao, Hongli,Li, Yajun,Su, Min,Wan, Wen-Ming,Zhu, Nengbo
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supporting information
(2020/02/15)
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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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- 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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- 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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- Application of coumarin dyes for organic photoredox catalysis
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Here we report the application of readily prepared and available coumarin dyes for photoredox catalysis, which are able to mimic powerful reductant [Ir(iii)] complexes. Coumarin derivatives 9 and 10 were employed as photoreductants in pinacol coupling and in other reactions, in the presence of Et3N as a sacrificial reducing agent. As the electronic, photophysical, and steric properties of coumarins could be varied, a wide applicability to several classes of photoredox reactions is predicted.
- Gualandi, Andrea,Rodeghiero, Giacomo,Della Rocca, Emanuele,Bertoni, Francesco,Marchini, Marianna,Perciaccante, Rossana,Jansen, Thomas Paul,Ceroni, Paola,Cozzi, Pier Giorgio
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supporting information
p. 10044 - 10047
(2018/09/13)
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- MeOH or H2O as efficient additive to switch the reactivity of allylSmBr towards carbonyl compounds
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A variety of carbonyl compounds were treated by allylSmBr (allylSmBr) with MeOH as the cosolvent to have further insights on the previously reported reductive coupling of aryl ketones mediated by Sm/alkyl halide/MeOH. The results demonstrate that the real reducing species in Sm/alkyl halide/MeOH system should be allylSmBr, and MeOH has elegantly switched the reactivity of allylSmBr from being nucleophilic to being good reductive coupling reagent. Besides, H2O was also found to be a useful additive to realize the pinacol coupling of aliphatic aldehydes and ketones promoted by allylSmBr.
- Li, Jianyong,Niu, Qingsheng,Li, Shanchan,Sun, Yuehao,Zhou, Qian,Lv, Xin,Wang, Xiaoxia
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supporting information
p. 1250 - 1253
(2017/03/10)
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- Metal-free reductive coupling of CO and CN bonds driven by visible light: Use of perylene as a simple photoredox catalyst
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Perylene, a simple polycyclic aromatic hydrocarbon, was used as a photoredox catalyst to enable the reductive coupling reaction of aromatic aldehydes, ketones, and an imine under visible-light irradiation using a white LED.
- Okamoto, Shusuke,Kojiyama, Keita,Tsujioka, Hiroki,Sudo, Atsushi
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supporting information
p. 11339 - 11342
(2016/09/23)
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- Magnesium-Alkoxide directed photoaddition of tetrahydrofurans to γ,γ-disubstituted allylic alcohols
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Magnesium-Alkoxide directed photoaddition of tetrahydrofurans to γ,γ-disubstituted allylic alcohols was achieved. When the allylic alcohols were treated with Grignard reagent in THF under light, the corresponding γ-(2-Tetrahydrofuryl) substituted alcohols
- Watanabe, Yasutaka,Sakai, Takahiro,Maeda, Hajime,Segi, Masahito,Soeta, Takahiro,Ukaji, Yutaka
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p. 833 - 844
(2017/04/10)
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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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supporting information
p. 8828 - 8832
(2015/11/27)
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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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- A clean and selective radical homocoupling employing carboxylic acids with titania photoredox catalysis
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A titania photoredox catalysis protocol was developed for the homocoupling of C-centered radicals derived from carboxylic acids. Intermolecular reactions were generally efficient and selective, furnishing the desired dimers in good yields under mild neutral conditions. Selective cross-coupling with two acids proved unsuccessful. An intra-molecular adaptation enabled macrocycles to be prepared, albeit in modest yields. (Chemical Equation Presented).
- Manley, David W.,Walton, John C.
-
supporting information
p. 5394 - 5397
(2015/02/19)
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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
-
supporting information
p. 1143 - 1150
(2014/06/09)
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- Reductive coupling of N-methoxycarbonyl lactams with benzophenone and 9-fluorenone by low-valent titanium
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The reductive coupling of N-methoxycarbonyl lactams with benzophenone by Zn-TiCl4 in THF gave cross-coupled products as cyclic α-diphenylidene-N-methoxycarbonylamines and ring-opening α,α-diphenyl-α-hydroxy-ω-(N-methoxycarbonyl)amino ketones selectively depending on the reduction conditions. The reductive coupling of N-methoxycarbonyl lactams with 9-fluorenone by Zn-TiCl4 gave cyclic α-(9H-fluoren-9-ylidene)-N-methoxycarbonylamines preferentially irrespective to the conditions.
- Kise, Naoki,Takenaga, Yosei,Ishikawa, Yohei,Morikami, Yoichi,Sakurai, Toshihiko
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experimental part
p. 1940 - 1945
(2012/05/05)
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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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- Racemic (1,4-dioxan-2-yl)diphenylmethanol
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The title compound, C17H18O3, prepared by microwave irradiation of benzophenone and dioxane, crystallizes in a racemic mixture that forms onedimensional chains via strong hydrogen bonding of the hydroxy group to the adjacent symmetry-generated 1,4-dioxan-2-yl group; the O - H...O distance is 1.99 (3) A and the O - H...O angle is 160 (2)°.
- Hsiao, Tomi,Buchanan, Robert M.,Mashuta, Mark S.
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experimental part
p. o129-o130
(2011/05/07)
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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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- Probing lipid peroxidation by using linoleic acid and benzophenone
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A thorough mechanistic study has been performed on the reaction between benzophenone (BZP) and a series of 1,4-dienes, including 1,4-cyclohexadiene (CHD), 1,4-dihydro-2-methylbenzoic acid (MBA), 1,4-dihydro-1,2-dimethylbenzoic acid (DMBA) and linoleic acid (LA). A combination of steady-state photolysis, laser flash photolysis (LFP), and photochemically induced dynamic nuclear polarization (photo-CIDNP) have been used. Irradiation of BZP and CHD led to a cross-coupled sensitizer-diene product, together with 6, 7, and 8. With MBA and DMBA as hydrogen donors, photoproducts arising from cross-coupling of sensitizer and diene radicals were found; compound 7 was also obtained, but 6 and o-toluic acid were only isolated in the irradiation of BZP with MBA. Triplet lifetimes were determined in the absence and in the presence of several diene concentrations. All three model compounds showed similar reactivity (k q≈108 M-1 s-1) towards triplet excited BZP. Partly reversible hydrogen abstraction of the allylic hydrogen atoms of CHD, MBA, and DMBA was also detected by photo-CIDNP on different timescales. Polarizations of the diamagnetic products were in full agreement with the results derived from LFP. Finally, LA also underwent partly reversible hydrogen abstraction during photoreaction with BZP. Subsequent hydrogen transfer between primary radicals led to conjugated derivatives of LA. The unpaired electron spin population in linoleyl radical (LA.) was predominantly found on H(1-5) protons. To date, LA-related radicals were only reported upon hydrogen transfer from highly substituted model compounds by steady-state EPR spectroscopy. Herein, we have experimentally established the formation of LA. and shown that it converts into two dominating conjugated isomers on the millisecond timescale. Such processes are at the basis of alterations of membrane structures caused by oxidative stress. Copyright
- Andreu, Inmaculada,Neshchadin, Dmytro,Rico, Enrique,Griesser, Markus,Samadi, Abdelouahid,Morera, Isabel M.,Gescheidt, Georg,Miranda, Miguel A.
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experimental part
p. 10089 - 10096
(2011/10/13)
-
- Concentration and temperature dependency of regio- and stereoselectivity in a photochemical [2 + 2] cycloaddition reaction (the Paterno-Buechi reaction): Origin of the hydroxy-group directivity
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A set of photochemical oxetane formation reactions, i.e., the Paterno-Buechi (PB) reactions, of tetrahydrobenzofuranol derivatives 1a-d with benzophenone (BP) was investigated to examine poorly understood hydroxy-group directivity on regio- and stereoselectivity. The selectivities of the PB reactions for allylic alcohols 1a,d were found to be largely dependent upon the concentration of the allylic alcohols and the reaction temperature. The temperature-dependent change of the regioselectivity at high concentrations of allylic alcohols was similar to that of the hydroxy-protected methyl ether 1b and tetrahydrobenzofuran (1c). The effect of concentration on regioselectivity can be explained by the hydrogen-bonded aggregates, which mimic the selectivities observed during the PB reaction of 1b,c. The hydroxy-directed cis-selectivity of the higher-substituted oxetane 3a,d formed at low concentration of 1a,d was found to be larger than that at the higher concentration of 1a,d. The cis-selectivity of 3a,d was found to be higher than that of the lower-substituted oxetane 2a,d. The regioselectivity of the cis-configured oxetanes was higher than that of the trans-configured oxetanes. These experimental results strongly suggest that hydroxy-group directivity, induced by hydrogen-bonding stabilization, plays a role in controlling the regio- and stereoselectivity of the PB reactions. The steric effect was also responsible for the diastereoselectivity, as shown by the fact that the cis selectivity in 3d was higher than that in 3a. Computational studies at the (U)MP2 and (U)DFT level of theory revealed that hydrogen-bonding stabilization becomes important only in the excited complex (exciplex) between the triplet excited state of carbonyls and alkenes, in which the charge transfer occurs from the alkene to the excited carbonyl to make the carbonyl oxygen nucleophilic. No significant stabilization energy was found in the intermediary triplet state of biradicals. The combined experimental and computational studies have clarified the origin of the poorly understood hydroxy-group effect on a high degree of regio- and stereoselectivity, i.e., the cooperative effect of hydrogen-bonding stabilization in exciplexes and the steric bulk of the substituents.
- Yabuno, Youhei,Hiraga, Yoshikazu,Takagi, Ryukichi,Abe, Manabu
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experimental part
p. 2592 - 2604
(2011/04/23)
-
- Hydroxy-group effect on the regioselectivity in a photochemical oxetane formation reaction (the Paterno-Buechi Reaction) of geraniol derivatives
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The Paterno-Buechi (PB) reaction of geraniol derivatives 1, which contain allylic alcohol functionality and unfunctionalized double bonds, with benzophenone was investigated to see the effect of the hydroxyl group on the regioselectivity of the oxetane formation, i.e., 2/3. At low concentration of geraniol (1a), oxetanes 2a and 3a were formed in a ratio of 2a/3a = ca. 50/50. The oxetane 2a is derived from the PB reaction at the allylic alcohol moiety, whereas the PB reaction at the unfunctionalized double bond produces the oxetane 3a. The PB reaction of the hydroxy-protected methyl ether 1b and acetate 1c gave selectively oxetanes 3b,c derived from the reaction at the more nucleophilic double bond, 2/3 ~ 15/85. The hydroxyl-group effect was found to be small, but apparently increased the formation of 2a in the PB reaction with geraniol (1a). The Royal Society of Chemistry and Owner Societies.
- Hisamoto, Ken,Hiraga, Yoshikazu,Abe, Manabu
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experimental part
p. 1469 - 1473
(2012/06/18)
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- Novel alkylidenating agents of iron(III) derivatives by base-mediated α,μ-dehydrohalogenation and their chemical trapping by cycloaddition
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Studies of the reactions between group 4 metal, chlorides (M = Ti, Zr, Hf) and methyllithium at -78 °C in toluene can lead to methylidene-metal complexes, H2C=MCl2, by a sequence of monomethylation, α-carbon lithiation and α,μ-elimination of LiCl. Here study of the preparation of alkylidene derivatives of iron was attempted by the interaction of FeCl3 with n-butyllithium in various ratios at -78 °C. The presence of any resulting butylidene-iron(III) derivative, nPrCH=FeE (E = Cl, nBu), was probed by adding chemical trapping agents, such as diphenylacetylene, benzonitrile, methyl benzoate and benzophenone. In each experiment the hydrolyzed products were consistent with a cycloaddition reaction of nPrCH=FeE with the trapping agent. The products from, di-phenylacetylene and from, benzonitrile with D2O workup are uniquely in accord with such a carbene precursor. A 3:1 ratio of nBuLi/FeCl3 gave the optimal yield of nPrCH=FenBu, ca. 80%, from, the MBu2FeCl precursor. When a 3:1. reaction mixture was simply brought to 25 °C and hydrolyzed, the purple alkylidene-iron complex decomposed completely to iron metal. A study of a 3:1 interaction of PhCH2MgCl and FeCl3 under similar conditions and trapping with diphenylacetylene provided evidence for the formation of PhCH=FeCH2Ph in ca. 40%. These results support; the hope that alkylidene-iron(III) analogs of the Grubbs reagents may be accessible by this process.
- Eisch, John J.,Sohn, Jane U.,Rabinowitz, Edon J.
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experimental part
p. 2971 - 2977
(2010/08/20)
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- Vanadium(I) chloride and lithium vanadium(I) dihydride as selective epimetallating reagents for π- and σ-bonded organic substrates
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Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, whose efficient preparation, structural constitution and mode of reaction toward certain organic substrates have been described in a preceding article, are here evaluated in their reactions toward a wide variety of π- and σ-bonded organic substrates, namely carbonyl, imine, azo, alkene, 1,3-diene, nitrile π-bonds and C-X, C-O, C-N and N-N σ-bonds. Compared with the high reactivity of CrCl and LiCrH2 reagents in attacking both types of bonds, the VCl and LiVH2 reagents were much milder and selective in epimetallating π-bonds, often forming the 1:1 adduct of LiVH2 and π-bonded substrate as the major product. Finally, the vanadium reagents showed little tendency to cleave C-O, C-S and C-N bonds and a smaller scope in cleaving C-X bonds than their chromium counterparts. Because of their selectivity these vanadium reagents offer the following preparative promise: 1) smooth McMurry carbonyl coupling to their reductive dimers; 2) deoxygenation of epoxides; 3) selective aromatic C-X reduction; 4) high yields of epimetallated carbonyls or imines as intermediates to α-hydroxy and α-amino acids; 5) 1,4-reductions of 1,3-alkadienes; 6) reductive dimerization of nitriles to ketones; 7) 1,4 or 1,n-epimetallations leading to acyloins or indoles; and 8) reductive dimerizations of azines to produce unusual imidazole derivatives. In explaining the greater kinetic stability of the 1:1 LiVH2 adduct with carbonyl or imine substrates it is pointed out that such epimetallated adducts from LiVH2 would likely be diamagnetic, whereas such adducts from LiCrH2 have an unpaired electron on the Cr center and hence would rupture, so that the electron would be on the C center. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Eisch, John J.,Fregene, Paul O.
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scheme or table
p. 4482 - 4492
(2009/05/07)
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- Site- and stereoselectivity in the photochemical oxetane formation reaction (Paterno-Buechi reaction) of tetrahydrobenzofuranols with benzophenone: hydroxy-directed diastereoselectivity?
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The Paterno-Buechi reactions of tetrahydrobenzofuranols with benzophenone were investigated to reveal site- and stereo-selectivity in oxetane formation reactions. Both selectivities were found to be largely dependent on the reaction temperature. The trans selectivity increased with a decrease in temperature, and the more-substituted oxetanes were selectively formed at high temperature. Copyright
- Yabuno, Youhei,Hiraga, Yoshikazu,Abe, Manabu
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p. 822 - 823
(2008/12/22)
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- InCl3/Al mediated pinacol coupling reactions of aldehydes and?ketones in aqueous media
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A systematic work on the homo-pinacol coupling reactions of benzophenones, aldehydes, and acetophenones in aqueous media with InCl3/Al is described for the first time, in which various 1,2-diols are obtained in moderate to good yields.
- Wang, Chunyan,Pan, Yuanjiang,Wu, Anxin
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p. 429 - 434
(2007/10/03)
-
- Pinacol coupling of aromatic aldehydes and ketones mediated by TiCl 4-Zn in ethyl acetate under ultrasound
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Zinc powder can reduce titanium tetrachloride to the corresponding low valent titanium complexes, which can promote coupling of some aromatic aldehydes and ketones to the corresponding pinacols in 35-99% yield in ethyl acetate at 20-25°C within 20-45 min under ultrasound irradiation.
- Li, Ji-Tai,Sun, Xue-Li,Lin, Zhi-Ping,Chen, Yan-Xue,Li, Tong-Shuang
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p. 1303 - 1307
(2008/09/18)
-
- Triplet energy dissipation in methylenecyclopropane rearrangement
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(Chemical Equation Presented) Certain 1,1-dimethyl-2-aryl-3- methylenecyclopropanes containing carbonyl substituents undergo rearrangement when irradiated with 350 nm light. These rearrangements occur via the (n,π*) triplet state, which fragments the stra
- Creary, Xavier,Losch, Andrea,Sullivan, William
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p. 7930 - 7938
(2008/02/13)
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- An efficient C-C bond cleavage of 1,2-diols using tetraethylammonium superoxide
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Tetraethylammonium superoxide, generated in situ by the phase-transfer reaction of potassium superoxide and tetraethylammonium bromide in DMF, brings about an easy cleavage of vicinal diols and related dihydroxy arenes under mild reaction conditions, at room temperature.
- Singh, Krishna Nand,Kumar, Rajesh,Shukla, Ajay Kumar
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p. 1347 - 1351
(2008/09/18)
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- Solid-state photocycloaddition of 6,6′-dimethyl-4,4′-[bis(methylenoxy)phenylene]-di-2-pyrones with benzophenone
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Photocycloaddition reactions of 6,6′-dimethyl-4,4′-[bis(methylenoxy)phenylene]-di-2-pyrones (4a-c) with benzophenone (2a) by mixing in the solid state (solid solution) afforded the corresponding oxetane derivatives (5a-c; 1:2 adducts) with high site- and regioselectivity across the C5-C6 and C5′-C6′ double bonds in 4 via the triplet excited state of benzophenone. The oxetane formation proceeded more effectively in the solid state than in solution. The reaction mechanism was inferred by MO methods to be initiated by electrostatic interaction between the C6 position of 4a-c and the carbonyl oxygen of 2a in their ground states. The solid-state interaction may be enhanced by the electron density at the carbonyl oxygen of the triplet 2a. The transition state (TS) analysis of the [2+2] cycloaddition reactions also suggested some triplet complexes and high regioselectivity. The hydrogen-bonding interaction between 2a and 4a-c and the triplet reaction mechanism were also explained by the IR analyses and the quenching experiments, respectively.
- Wang, Weidong,Shimo, Tetsuro,Hashimoto, Hiroaki,Somekawa, Kenichi
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p. 12367 - 12372
(2008/03/14)
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- Pinacol coupling of carbonyl compounds by using Al-NaOH/MeOH under microwave irradiation
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Reductive coupling of aromatic aldehydes and ketones to the corresponding 1,2-diols has been achieved in 59-98% yields using aluminium powder in aqueous sodium hydroxide and methanol medium under microwave irradiation for 5-12 min. The notable advantage of this method seems to be negligible formation of simple amounts of reduced product of the carbonyls i.e. alcohols and the formation of side product olefins via McMurry coupling. The reaction rate is fast and the purity of products is compared to the existing methods. The potential Pinacol rearrangement of the reductive coupling products greatly extends their synthetic utility.
- Tehrani, Mohsen Mazaheri,Asghari, Jila
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p. 332 - 334
(2007/10/03)
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- Notable temperature effect on the stereoselectivity in the photochemical [2+2] cycloaddition reaction (Paternò-Büchi reaction) of 2,3-dihydrofuran-3-ol derivatives with benzophenone
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A notable temperature effect (nonlinear Eyring plot) on stereoselectivity, trans-configured oxetane 2 versus cis-configured oxetane 2, is reported in the photochemical [2+2] cycloaddition reaction (Paternò-Büchi reaction) of 2,3-dihydrofuran-3-ol derivatives 1 with benzophenone.
- Abe, Manabu,Terazawa, Midori,Nozaki, Koichi,Masuyama, Araki,Hayashi, Takashi
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p. 2527 - 2530
(2007/10/03)
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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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- Pinacol coupling of aromatic aldehydes and ketones in ethyl acetate mediated by TiCl4-Mg
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Titanium tetrachloride in ethyl acetate can be reduced by Mg powder to the corresponding low-valent titanium complexes, which can reduce some aromatic aldehydes and ketones to the corresponding pinacols in 38-85% yields within 15-60 min at rt with stirring. Copyright Taylor & Francis Group, LLC.
- Wang, Ke,Wang, Shu-Xiang,Gao, Ming-Zhu,Li, Ji-Tai
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p. 1391 - 1399
(2007/10/03)
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- Studies on the lanthanum-induced pinacol coupling of aromatic aldehydes and ketones in aqueous media
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The pinacol coupling of aromatic aldehydes and ketones was carried out in 16-71% yield using La-36%HAc-CH2Cl2 system with stirring at rt in 4 h. The reactions in the same system gave pinacols in 12-91% yield under ultrasound irradiation at rt in 2 h. Copyright Taylor & Francis Group, LLC.
- Bian, Yan-Jiang,Yu, Xu-Guang,Peng, Hong-Wei,Li, Ji-Tai
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p. 2513 - 2518
(2007/10/03)
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- Reduction of benzophenone by SmI2: The role of proton donors in determining product distribution
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(Graph Presented) Reduction of benzophenone by SmI2 yields benzopinacol. Addition of proton donors results in an initial increase in the amount of the benzhydrol formed. However, the ratio benzhydrol/benzopinacol reaches a maximum, decreases, and then levels off as the proton donor concentration is further increased. The position of the maximum and its height depend on the proton donor concentration and its kinetic acidity. The momentary concentration of the intermediate radicals governs the product distribution.
- Kleiner, Gregory,Tarnopolsky, Alexander,Hoz, Shmaryahu
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p. 4197 - 4200
(2007/10/03)
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- Contrastive photoreduction pathways of benzophenones governed by regiospecific deprotonation of imidazoline radical cations and additive effects
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In the photoreaction of benzophenones with 1,3-dimethyl-2- phenylbenzimidazoline (DMPBI), benzhydrols were major products. Addition of H2O accelerated the reaction with no change in the product distribution, while AcOH, PhOH, and metal salts such as LiClO4 and Mg(ClO4)2 were effective additives to produce benzpinacols. In contrast, benzpinacols were exclusively formed regardless of the solvent and the additive in the reactions with 2-(o-hydroxyphenyl)-1,3- dimethylbenzimidazoline (o-HPDMBI). These observations are consistent with the hypothesis that DMPBI.+ donates a proton at the C2 position to the benzophenone ketyl radicals while o-HPDMBI.+ donates a phenol proton.
- Hasegawa, Eietsu,Seida, Takayuki,Chiba, Naoki,Takahashi, Tomoya,Ikeda, Hiroshi
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p. 9632 - 9635
(2007/10/03)
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- Magnesium-induced pinacol coupling of aromatic aldehydes and ketones under ultrasound irradiation
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The system of magnesium and magnesium iodide can reduce some aromatic aldehydes and ketones to the corresponding pinacols in good yields within 10-60 min at room temperature under ultrasound irradiation. Copyright Taylor & Francis, Inc.
- Wang, Jian-Sen,Li, Ji-Tai,Lin, Zhi-Ping,Li, Tong-Shuang
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p. 1419 - 1424
(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)
-