- Oxidative carbon-carbon bond cleavage of 1,2-diols to carboxylic acids/ketones by an inorganic-ligand supported iron catalyst
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The carbon-carbon bond cleavage of 1,2-diols is an important chemical transformation. Although traditional stoichiometric and catalytic oxidation methods have been widely used for this transformation, an efficient and valuable method should be further explored from the views of reusable catalysts, less waste, and convenient procedures. Herein an inorganic-ligand supported iron catalyst (NH4)3[FeMo6O18(OH)6]·7H2O was described as a heterogeneous molecular catalyst in acetic acid for this transformation in which hydrogen peroxide was used as the terminal oxidant. Under the optimized reaction conditions, carbon-carbon bond cleavage of 1,2-diols could be achieved in almost all cases and carboxylic acids or ketones could be afforded with a high conversion rate and high selectivity. Furthermore, the catalytic system was used efficiently to degrade renewable biomass oleic acid. Mechanistic insights based on the observation of the possible intermediates and control experiments are presented.
- Chen, Weiming,Xie, Xin,Zhang, Jian,Qu, Jian,Luo, Can,Lai, Yaozhu,Jiang, Feng,Yu, Han,Wei, Yongge
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supporting information
p. 9140 - 9146
(2021/11/23)
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- Mo–Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties
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A catalytic domino reduction–imine formation–intramolecular cyclization–oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.
- Hernández-Ruiz, Raquel,Rubio-Presa, Rubén,Suárez-Pantiga, Samuel,Pedrosa, María R.,Fernández-Rodríguez, Manuel A.,Tapia, M. José,Sanz, Roberto
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supporting information
p. 13613 - 13623
(2021/08/23)
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- Metal-free thermal organocatalytic pinacol coupling of arylaldehydes using an isonicotinate catalyst with bis(pinacolato)diboron
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The metal-free thermal organocatalytic pinacol coupling of arylaldehydes has been developed. The intermolecular coupling of arylaldehydes catalyzed byt-butyl isonicotinate with bis(pinacolato)diboron as the co-reducing agent afforded 1,2-diphenylethane-1,2-diols. This reaction was also applicable to the intramolecular coupling of 1,1′-biphenyl-2,2′-dicarbaldehydes to afford 9,10-dihydrophenanthrene-9,10-diols. Various functional groups were tolerated under this coupling condition.
- Hanaya, Kengo,Higashibayashi, Shuhei,Sugai, Takeshi,Yasui, Masamichi
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p. 24652 - 24655
(2021/07/29)
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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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- 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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- Stereoselective Barbier-Type Allylations and Propargylations Mediated by CpTiCl3
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CpTiCl2, prepared in situ by manganese reduction of CpTiCl3, is an excellent new system for the Barbier-type allylation and propargylation of carbonyl compounds. It can be used in catalytic amounts when combined with Et3N·HBr/TMSBr, which acts as a regenerating system. The high regio- and stereoselectivity shown by this system makes it useful for prenylation and crotylation processes in the synthesis of natural products.
- López-Martínez, Josefa L.,Torres-García, Irene,Rodríguez-García, Ignacio,Mu?oz-Dorado, Manuel,álvarez-Corral, Miriam
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p. 806 - 816
(2019/01/24)
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- Hydrogen Bonding-Assisted Enhancement of the Reaction Rate and Selectivity in the Kinetic Resolution of d,l-1,2-Diols with Chiral Nucleophilic Catalysts
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An extremely efficient acylative kinetic resolution of d,l-1,2-diols in the presence of only 0.5 mol% of binaphthyl-based chiral N,N-4-dimethylaminopyridine was developed (selectivity factor of up to 180). Several key experiments revealed that hydrogen bonding between the tert-alcohol unit(s) of the catalyst and the 1,2-diol unit of the substrate is critical for accelerating the rate of monoacylation and achieving high enantioselectivity. This catalytic system can be applied to a wide range of substrates involving racemic acyclic and cyclic 1,2-diols with high selectivity factors. The kinetic resolution of d,l-hydrobenzoin and trans-1,2-cyclohexanediol on a multigram scale (10 g) also proceeded with high selectivity and under moderate reaction conditions: (i) very low catalyst loading (0.1 mol%); (ii) an easily achievable low reaction temperature (0 °C); (iii) high substrate concentration (1.0 M); and (iv) short reaction time (30 min). (Figure presented.).
- Fujii, Kazuki,Mitsudo, Koichi,Mandai, Hiroki,Suga, Seiji
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supporting information
p. 2778 - 2788
(2017/08/23)
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- Biginelli reaction of vicinal diols: A new route for one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives
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Background: 3,4-Dihydropyrimidin-2(1H)-one derivatives are an important class of nitrogen heterocycles. These compounds present a wide range of biological activities viz antibacterial, antifungal, and antidiabetic. Although many synthetic methods are available in the literature for the synthesis of these molecules, many of these methods have their own limitations such as use of excess of expensive catalyst and poor yields. Methods: The synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives is developed through the reaction of 1,2-diols, ethyl acetoacetate and urea in the presence of lead tetraacetate in dry ethanol under reflux conditions. Results: A series of 3,4-dihydropyrimidin-2(1H)-one derivatives were synthesized in good yields (82-95%) under reflux for 2-3.5 hours in ethanol solvent. The structural assignments of these compounds were made on the basis of elemental analysis and spectroscopic data. Conclusion: This protocol is an alternative to existing procedure for the synthesis of Biginelli compounds. The present methodology reduces the number of steps in total synthesis.
- Jagadishbabu, Narasashetty,Shivashankar, Kalegowda
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p. 330 - 336
(2017/07/26)
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- Polarity-Reversed Allylations of Aldehydes, Ketones, and Imines Enabled by Hantzsch Ester in Photoredox Catalysis
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The polarity reversal (umpolung) reaction is an invaluable tool for reversing the chemical reactivity of carbonyl and iminyl groups, which subsequent cross-coupling reactions to form C?C bonds offers a unique perspective in synthetic planning and implementation. Reported herein is the first visible-light-induced polarity-reversed allylation and intermolecular Michael addition reaction of aldehydes, ketones, and imines. This chemoselective reaction has broad substrate scope and the engagement of alkyl imines is reported for the first time. The mechanistic investigations indicate the formation of ketyl (or α-aminoalkyl) radicals from single-electron reduction, where the Hantzsch ester is crucial as the electron/proton donor and the activator.
- Qi, Li,Chen, Yiyun
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supporting information
p. 13312 - 13315
(2016/10/30)
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- An imidazolium-modified chiral rhodium/diamine-functionalized periodic mesoporous organosilica for asymmetric transfer hydrogenation of α-haloketones and benzils in aqueous medium
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The use of a hydrophobic, imidazolium-functionalized periodic mesoporous organosilica for immobilization of chiral organometallic complexes as a heterogeneous catalyst is highly desirable as this catalyst can greatly promote an aqueous organic transformation due to its hydrophobic function and phase-transfer feature in an aqueous medium. Herein, by utilizing a three-component co-condensation strategy, we conveniently incorporate 1,2-bis(triethoxysilyl)ethane, (R,R)-4-((trimethoxysilyl)ethyl)phenylsulfonyl-1,2-diphenylethylene-diamine and 1,3-bis(3-(triethoxysilyl)propyl)-1H-imidazol-3-ium iodide within its silicate network, which is coordinated with (Cp?RhCl2)2, leading to an imidazolium-modified chiral rhodium/diamine-functionalized periodic mesoporous organosilica. A solid-state carbon spectrum discloses its well-defined chiral rhodium/diamine active species, and its X-ray diffraction; nitrogen adsorption-desorption measurement and transmission electron microscopy images reveal its ordered dimensional-hexagonal mesostructure. As a bifunctional heterogeneous catalyst, this periodic mesoporous organosilica significantly boosts asymmetric transfer hydrogenation of α-haloketones and benzils in water, where the hydrophobic periodic mesoporous organosilica, phase-transfer-featured imidazolium-functionality, and the confined chiral organorhodium catalytic nature are responsible for its catalytic performance. Furthermore, the catalyst can be recovered and recycled seven times without the loss of its catalytic activity, making it an attractive heterogeneous catalyst for asymmetric transfer hydrogenation in an environmentally friendly manner.
- Zhou, Feng,Hu, Xiaoying,Gao, Ming,Cheng, Tanyu,Liu, Guohua
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p. 5651 - 5657
(2016/10/21)
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- Selective Pinacol-Coupling Reaction using a Continuous Flow System
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The first continuous flow pinacol coupling reaction of carbonyl compounds was successfully achieved within only 2 min during a single pass through a cartridge filled with zinc(0). The optimized method allowed the efficient production of gram-scale value-added compounds with high productivity. The developed methodology is efficient for aromatic or α,β-unsaturated aldehydes but gives moderate results for more stable acetophenone derivatives. Moreover, the flow method displayed better results in terms of yield and selectivity in comparison to the corresponding batch methodology.
- Sotto, Nicolas,Cazorla, Clément,Villette, Carole,Billamboz, Muriel,Len, Christophe
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p. 11065 - 11071
(2016/11/28)
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- First pinacol coupling in emulsified water: Key role of surfactant and impact of alternative activation technologies
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For the first time, the influence of surfactants on the radical pinacol coupling reaction is investigated. The rate and selectivity of this reductive C-C coupling are compared under three different activation technologies: thermal activation, microwave irradiation, and sonication. The use of IgepalCO520, a neutral surfactant, led to the successful conversion of aromatic or α,β-unsaturated aliphatic carbonyl compounds in moderate to excellent yield (55-90 %). An insight on the potential mechanism involved in the reaction is also proposed, based on microscopic observations and particle size measurement.
- Billamboz, Muriel,Len, Christophe
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p. 1664 - 1675
(2015/06/02)
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- Alkene anti-Dihydroxylation with Malonoyl Peroxides
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Malonoyl peroxide 1, prepared in a single step from the commercially available diacid, is an effective reagent for the anti-dihydroxylation of alkenes. Reaction of 1 with an alkene in the presence of acetic acid at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (35-92%) with up to 13:1 anti-selectivity. A mechanism consistent with experimental findings is proposed that accounts for the selectivity observed.
- Alamillo-Ferrer, Carla,Davidson, Stuart C.,Rawling, Michael J.,Theodoulou, Natalie H.,Campbell, Matthew,Humphreys, Philip G.,Kennedy, Alan R.,Tomkinson, Nicholas C. O.
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supporting information
p. 5132 - 5135
(2015/11/03)
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- Selective Pinacol Coupling on Regeneratable Supported Acids in Sole Water
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Efficient pinacol coupling was developed in sole water, using a reusable heterogeneous supported acid source and zinc as cheap available metal source. This medium can be easily regenerated up to 10-fold without loss of activity. Moreover, supported acids enhance the selectivity of the pinacol coupling reaction compared with homogeneous acids.
- Sotto, Nicolas,Billamboz, Muriel,Chevrin-Villette, Carole,Len, Christophe
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p. 6375 - 6380
(2015/06/30)
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- Pinacol couplings of a series of aldehydes and ketones with SmI2/Sm/Me3SiCl in DME
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The pinacol coupling is one of the most significant methods to synthesize vic-diols. The combination of samarium diiodide (SmI2) and samarium metal successfully induces the selective pinacol couplings of not only aromatic aldehydes and ketones but also aliphatic ones in the presence of trimethylchlorosilane (Me3SiCl) in 1,2-dimethoxyethane (DME). DME is the most suitable solvent for the reduction system using SmI2 and Me3SiCl. Me3SiCl, a widely available additive, prevents the decomposition of the formed vic-diols, i.e., meso-isomers, and controls their stereochemistry. In particular, the pinacol couplings of sterically hindered aliphatic aldehydes and ketones proceed with excellent diastereoselectivities to afford dl-isomers in good yields.
- Yoshimura, Aya,Saeki, Tomokazu,Nomoto, Akihiro,Ogawa, Akiya
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p. 5347 - 5355
(2015/07/15)
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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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- 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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- Enantioselective oxidation of 1,2-diols with quinine-derived urea organocatalyst
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Quinine-derived urea has been identified as a highly efficient organocatalyst for the enantioselective oxidation of 1,2-diols using bromination reagents as the oxidant. This simple procedure utilizes readily available reagents and operates at ambient temperature to yield a wide range of α-hydroxy ketones in good yield (up to 94%) and excellent enantioselectivity (up to 95% ee).
- Rong, Zi-Qiang,Pan, Hui-Jie,Yan, Hai-Long,Zhao, Yu
-
supporting information
p. 208 - 211
(2014/01/23)
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- Transition-metal-free and chemoselective NaOtBu-O 2-mediated oxidative cleavage reactions of vic-1,2-diols to carboxylic acids and mechanistic insight into the reaction pathways
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A method for efficient oxidative cleavage of vic-1,2-diols using a NaO tBu-O2 system resulted in the formation of carboxylic acids in high yields. The present protocol is an eco-friendly alternative to a conventional transition-metal-based method. This new strategy allows large-scale production with nonchromatographic purification while also suppressing competitive reaction pathway such as benzilic acid rearrangement.
- Kim, Sun Min,Kim, Dong Wan,Yang, Jung Woon
-
supporting information
p. 2876 - 2879
(2014/06/23)
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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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- Synthesis of ferrocene derivatives with planar chirality via palladium-catalyzed enantioselective C-H bond activation
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The first catalytic and enantioselective C-H direct acylation of ferrocene derivatives has been developed. A series of 2-acyl-1-dimethylaminomethylferrocenes with planar chirality were provided under highly efficient and concise one-pot conditions with up to 85% yield and 98% ee. The products obtained could be easily converted to various chiral ligands via diverse transformations.
- Pi, Chao,Cui, Xiuling,Liu, Xiuyan,Guo, Mengxing,Zhang, Hanyu,Wu, Yangjie
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supporting information
p. 5164 - 5167
(2014/12/11)
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- Electrochemical pinacol coupling of aromatic carbonyl compounds in a [BMIM][BF4]-H2O mixture
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The electrochemical pinacol coupling reactions of aromatic carbonyl compounds were carried out using an 80% [BMIM][BF4]-H2O mixture as the electrolytic medium. The corresponding diols were obtained in good to excellent yields with moderate diastereoselectivity. The stereoselectivity can be explained using the strongly-bound ion-pairs formed between the imidazolium cation and the radical anions of the carbonyl compounds. The ionic liquid replaces both organic solvents and supporting electrolytes generally used in the electrosynthetic method. The electrolytic medium can be recycled and successfully reused at least in five consecutive reactions.
- Kronenwetter, Hannah,Husek, Jakub,Etz, Brian,Jones, Aaron,Manchanayakage, Renuka
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supporting information
p. 1489 - 1495
(2014/03/21)
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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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- Stereoselective synthesis of optically active hydrobenzoins via asymmetric hydrogenation of benzils with Ru(OTf)(TsDPEN)(I·6- cymene) as the pre-catalyst
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Optically active hydrobenzoins are very important building blocks for further derivation of biologically active complexes, natural products, and pharmaceutical compounds. In this paper, A practical approach has been developed for asymmetric hydrogenation
- Huang, Xiaofei,Li, Naikai,Geng, Zhicong,Pan, Fengfeng,Wang, Xingwang
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p. 2657 - 2663
(2013/01/15)
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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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- 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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- Novel synthesis of pinacols and sulfones promoted by Smi£ NiCl2 bimetallic system
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Smi£NiCl2 as a reductive system promoted reductive coupling of aryl adehydes and aryl ketone into pinacols in good yields and also promoted coupling reaction of aryl sulfonyl chlorides and active halides into sulfones in good yields.
- Ye, Yuyuan,Zhou, Qizhong,Zheng, Renhua,Jiang, Huajiang,Chen, Rener,Zhang, Yongmin
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experimental part
p. 331 - 334
(2012/05/04)
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- A novel application of [Cr(en)2]2+ in the synthesis of 1,2-diols from aromatic aldehydes
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A reductive pinacol type arylaldehyde homocoupling process mediated by the [Cr(en)2]2+ complex is described. This procedure affords the mavo-stereoisomer as the major product, an unexpected result considering that most organometallic methodologies preferentially yield the dl-isomer. Additionally, the method represents a novel application of the [Cr(en) 2]2+.
- Avila-Sorrosa, Alcives,Vega-Ramirez, Leticia,Rodriguez-Dominguez, Rafael,Salgado-Zamora, Hector,Peralta-Cruz, Javier,Reyes-Arellano, Alicia
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supporting information; experimental part
p. 500 - 501
(2010/08/22)
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- Enantioselective pinacol coupling reaction of aromatic aldehydes catalyzed by chiral vanadium complexes
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The asymmetric pinacol coupling of aromatic aldehydes by chiral salan-vanadium complexes as effective catalysts is reported. Chiral 1,2-diols were obtained with high diastereoselectivities (up to 90/10) and moderate to high enantioselectivities (up to 82%
- Sun, Jiangtao,Dai, Zhenya,Li, Changsi,Pan, Xu,Zhu, Chengjian
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experimental part
p. 3219 - 3221
(2010/01/11)
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- Reductive dehalogenation of arylhalides and alkylhalides with zinc in THF saturated aqueous ammonium chloride
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A low-cost and highly effective zinc/THF-saturated aqueous ammonium chloride has been developed for dehalogenation of arylhalides and alkylhalides in aqueous systems.
- Hekmatshoar, Rahim,Sajadi, Sodeh,Heravi, Majid M.
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experimental part
p. 616 - 618
(2009/05/07)
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- Reaction of secondary and tertiary aliphatic halides with aromatic aldehydes mediated by chromium(II): a selective cross-coupling of alkyl and ketyl radicals
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Takai-Utimoto reactions with secondary and tertiary aliphatic halides usually failed according to previous reports. Now, significant improvements could be achieved, and especially secondary aliphatic halides can be coupled to aromatic aldehydes in yields of up to >95%. A variety of processes are competing with the desired one, and thus conditions must be adapted to the nature of the aldehyde as well as the aliphatic halide used, as the outcome of these reactions is strongly affected by the putative radical intermediates.
- Wessjohann, Ludger A.,Schmidt, Gisela,Schrekker, Henri S.
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p. 2134 - 2142
(2008/09/18)
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- Reductive coupling of aromatic aldehydes promoted by an aqueous TiCl 3/tBuOOH system in alcoholic cosolvents
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The tert-butoxyl radical, generated by the aqueous TiIII/TBHP system, abstracts an H atom from alcoholic cosolvents (EtOH, iPrOH), leading to α-hydroxyalkyl radicals that reduce aromatic aldehydes to the corresponding 1,2-diols. The reactivities observed are explained by resonance stabilization of the α-hydroxybenzyl radicals formed in the electron-transfer (ET) process. Good Hammett-type correlations are obtained. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Clerici, Angelo,Greco, Cosimina,Panzeri, Walter,Pastori, Nadia,Punta, Carlo,Porta, Ombretta
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p. 4050 - 4055
(2008/02/13)
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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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- On the paradox of TiCl4 reducing power: Pinacol coupling and two-carbon homologation of carbonyl compounds
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TiCl4/DIPEA/CH2Cl2 reducing system promotes pinacol coupling and/or reduction to alcohol of aromatic aldehydes and carbonyl compounds activated towards reduction by an electron withdrawing group. In addition, bis homologation of these substrates is observed. An inner-sphere electron transfer from TiCl4 to DIPEA accounts for the products distribution.
- Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
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p. 1825 - 1827
(2007/10/03)
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- Alkylative Reduction of Titanium(IV) Isopropoxide with EtMgBr: Convenient Method for the Generation of Subvalent Titanium Alkoxide Reagents and their Reactivity in Pinacol Coupling Reactions
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The composition of the gaseous products from the reaction of Ti(IV) isopropoxide with ethylmagnesium bromide in diethyl ether evidences the formation of subvalent titanium isopropoxide species in various oxidation states depending on relative amounts of the reactants. Reaction of titanium(IV) isopropoxide with one equivalent of the Grignard reagent gives presumably titanium(III) isopropoxide. The latter is generated as a result of disproportionation of starting Ti(IV) species and titanium(II) isopropoxide-ethene complex which is formed as a result of ethane extrusion from diethyltitanium(IV) isopropoxide. Titanium(III) isopropoxide prepared by this way transforms the aldehydes and the aromatic ketones into the corresponding pinacols in good yields.
- Matiushenkov, Evgenii A.,Sokolov, Nikolai A.,Kulinkovich, Oleg G.
-
-
- Modified hydroborate agent: (2,2′-bipyridyl)(tetrahydroborato)zinc complex, [Zn(BH4)2(bpy)], as a new, stable, efficient ligand-metal hydroborate and chemoselective reducing agent
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(2,2′-Bipyridyl)(tetrahydroborato)zinc complex, [Zn(BH4)2(bpy)], is a new white stable compound which has been used for efficient reduction of variety of carbonyl compounds such as aldehydes, ketones, acyloins, α-diketones and α, β-unsaturated carbonyl compounds (1,2-reduction) to their corresponding alcohols in acetonitrile at room temperature. Excellent chemoselectivity was also observed for the reduction of aldehydes over ketones with this reducing agent.
- Zeynizadeh, Behzad
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p. 317 - 326
(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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- Pinacol Formation and Reduction of Aromatic Carbonyls with Magnesium-Methanol at Ambient Temperature
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A simple and inexpensive procedure for the pinacol formation of aromatic aldehydes and reduction of aromatic ketones to the corresponding alcohols with magnesium in dry methanol at ambient temperature is reported. The pinacol formation and reduction are proposed to be proceeding by SET from magnesium.
- Khurana, Jitender M.,Bansal, Geeti,Kukreja, Gagan,Pandey, Ravi R.
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p. 1365 - 1371
(2007/10/03)
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- Facile reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by an aqueous TiCl3/NH3 system: Selectivity and scope
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A simple and rapid procedure for the almost quantitative reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by use of TiCl3/NH3 in aqueous methanol solution is reported. The reducing system distinguishes between different classes of aldehydes and/or ketones, and many functionalities that usually do not survive under reducing conditions are tolerated well. The concept of reversal of chemoselectivity has also been developed. A mechanism based on two sequential one-electron transfers from TiIII to the carbonyl carbon atom is proposed, the second SET becoming operative only in the presence of ammonium ion (either added or formed in situ). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
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p. 3326 - 3335
(2007/10/03)
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- Enantioselective pinacol coupling of aldehydes mediated and catalyzed by chiral titanium complexes
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equation presented Starting from easily available chiral Schiff bases, a straightforward synthesis of air-stable titanium(IV) complexes was devised. Asymmetric pinacol coupling of aromatic aldehydes mediated and catalyzed by the corresponding low valent complexes afforded the chiral diols with high yields and enantioselectivities up to 91%. ? Universite catholique de Louvain. ? Universite Paris-Sud.
- Bensari, Ahlem,Renaud, Jean-Luc,Riant, Olivier
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p. 3863 - 3865
(2007/10/03)
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- Reductive coupling of carbonyl compounds to pinacols with zinc in THF-saturated aqueous ammonium chloride
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In the presence of metallic zinc, aldehydes and ketones experience reductive coupling in tetrahydrofuran-saturated aqueous ammonium chloride (5:3) to afford the corresponding pinacols in moderate to high yields.
- Hekmatshoar,Yavari,Beheshtiha,Heravi
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p. 689 - 691
(2007/10/03)
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- A highly dl-stereoselective pinacolization of aromatic aldehydes mediated by TiCl4-Zn
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Reduction of TiCl4(THF)4 with Zn in CH2Cl2 gave a green solution, which was found to promote the reductive coupling of aromatic aldehydes to yield 1,2-diols with high threo selectivity.
- Li, Tingyou,Cui, Wei,Liu, Jigang,Zhao, Jianzhang,Wang, Zongmu
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p. 139 - 140
(2007/10/03)
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- A novel method for pinacolic coupling of aromatic aldehydes and ketones with a Sm-ZnCl2 system
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Sm-ZnCl2-system-mediated reductive coupling of aromatic aldehydes and ketones in THF-H2O at room temperature affords the corresponding pinacols in moderate to good yields.
- Guo, Hongyun,Zhang, Yongmin
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p. 284 - 286
(2007/10/03)
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- Highly diastereoselective pinacol coupling of aldehydes catalyzed by titanium-schiff base complexes
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A new effective methodology for a highly diastereoselective pinacol coupling of aldehydes is described. The method employes 3 mol % of a complex prepared in situ from TiCl4(THF)2 and a Schiff base in acetonitrile. The catalytic cycle is realized with Me3SiCl and Mn as reducing agent. The dependence of the diastereoselectivity on the Schiff base used is reported.
- Bandini, Marco,Cozzi, Pier Giorgio,Morganti, Stefano,Umani-Ronchi, Achille
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p. 1997 - 2000
(2007/10/03)
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- Stereoselective pinacol coupling of planar chiral (benzaldehyde)Cr(Co)3, (benzaldimine)Cr(CO)3, ferrocenecarboxaldehyde and (dienal)Fe(CO)3 complexes with samarium diiodide
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An intermolecular pinacol coupling of the Planar chiral tricarbonylchromium complexes of o-substituted benzaldehydes or benzaldimines with samarium(II) diiodide in THF produces exclusively threo 1.2-diols or 1,2-diamines in an optically pure form, while the corresponding racemic o- substituted benzaldehyde or benzaldimine chromium complexes give a mixture of threo and erythro pinacol coupling products in a various ratio depending upon the nature of o-substituent. Similarly, planar chiral 2-substituted ferrocenecarboxaldehydes and (dienal)Fe(CO)3 produce the corresponding 1.2- diols with high stereoselectivity. The generated transition metal-complexed ketyl radical intermediates are configurationally stable with restriction to a rotation about C(α)-C(ipso) bond.
- Taniguchi, Nobukazu,Uemura, Motokazu
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p. 12775 - 12788
(2007/10/03)
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- Water accelerated Sm/TMSCl reduction system: Pinacolic coupling of aromatic carbonyl compounds and reductive dimerization cyclization of 1,1- dicyanoalkenes
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By action of Sm/TMSCl in THF at room temperature, aromatic carbonyl compounds produce the corresponding 1,2-diols via reductive coupling reaction and 1,1-dicyanoalkenes produce the functionalized cyclopentenes through reductive dimerization followed by intramolecular cyclization in one-pot. The former gives approximately equal amounts of (dl)- and (meso)-1,2-diols and the later gives the major trans-form products. Added micro amounts of water to the system not only can accelerate the reaction, but also increase the yields of products. Moreover, only substoichiometric quantities of metallic samarium are employed.
- Wang, Lei,Zhang, Yongmin
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p. 11129 - 11140
(2007/10/03)
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- Reductive pinacol coupling of aromatic carbonyl compounds catalytic in chromium(II)
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Reductive coupling of aromatic and heteroaromatic aldehydes and ketones bearing different functional groups to pinacols is effectively catalysed with 1-5 mol % of Cr(II) salts or chromocene in THF/DMF mixtures in the presence of manganese powder and trialkyl chlorosilanes. Excellent dl selectivity can be achieved albeit with lower yield using trialkylsilyl chlorides with bulky substituents.
- Svato?, Ale?,Boland, Wilhelm
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p. 549 - 551
(2007/10/03)
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- Sm(Hg) promoted pinacolic coupling of aromatic aldehydes and ketones
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The pinacolic coupling of aromatic aldehydes and ketones was performed with samarium/mercury amalgam in THF at room temperature to afford the corresponding 1,2-diols in good yields.
- Wang, Lei,Zhang, Yongmin
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p. 3991 - 3997
(2007/10/03)
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