- On the stereochemical outcome of the McMurry coupling of acetophenone. A reinvestigation
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In contrast to previous reports, the McMurry coupling reactions of acetophenone has been shown to give predominantly Z-2,3-diphenyl-2-butene.
- Andersson, Pher G.
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Read Online
- 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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- Facile pinacol coupling of aliphatic ketones by Brook rearrangement in the presence of samarium species
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Herein we report a practical pinacol coupling reaction, in which ketones (aldehydes) react smoothly with Sm and TMSBr to afford the diol products with Sm(II) or (III) siliyl species generated in situ. This reported method affords poor yields for aromatic ketone substrates and good yields for aliphatic ketones. Therefore, it distinguishes from most reductive coupling approaches that are more effective for aromatic carbonyl compounds and provides a facile and robust approach for the pinacol coupling of aliphatic ketones. Mechanistic studies also indicated the pinacolization probably proceeded via an anionic instead of radical coupling pathway involving the Brook rearrangement in the presence of samarium (II or III) silyl species.
- Wang, Xincan,Xie, Guanqun,Zhao, Yanfei,Zheng, Ke,Fang, Yanxiong,Wang, Xiaoxia
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supporting information
(2021/04/27)
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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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- 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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- Implementing Hydrogen Atom Transfer (HAT) Catalysis for Rapid and Selective Reductive Photoredox Transformations in Continuous Flow
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The reductive transformation of aryl halides and carbonyl compounds is a key step in many photoredox transformations. By combining a highly reducing organic photocatalyst with a thiol hydrogen atom transfer (HAT) catalyst, we showcase rapid and highly selective reactions of these synthetically important starting materials in continuous flow. The fast reduction of aryl iodides, bromides and chlorides has been demonstrated with residence times in some cases below one minute. Selectivity between mono- and di-dehalogenation could also be achieved in some cases. Aryl ketones, aldehydes and imines were shown to undergo facile pinacol couplings, and the coupling of an aryl chloride with a styrene was also successful.
- Steiner, Alexander,Williams, Jason D.,Rincón, Juan A,de Frutos, Oscar,Mateos, Carlos,Kappe, C. Oliver
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supporting information
p. 5807 - 5811
(2019/08/01)
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- Zinc-Mediated Efficient and Selective Reduction of Carbonyl Compounds
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We herein describe for the first time that an optimized combination of Zn and NH4Cl can be used for the selective reduction of aldehydes and ketones to the corresponding alcohols. The aldehyde and keto groups are selectively reduced in the presence of azide, cyano, epoxy, ester, and carbon–carbon double-bond functional groups. A broad functional-group compatibility, chemoselective reduction of aldehydes in the presence of ketones, and selective reduction of isatins at the C3 carbonyl group are the highlights of the present method.
- Mandal, Tirtha,Jana, Snehasish,Dash, Jyotirmayee
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p. 4972 - 4983
(2017/09/13)
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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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- 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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- 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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- 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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- 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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- Hydrogenations without hydrogen: Titania photocatalyzed reductions of maleimides and aldehydes
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A mild procedure for the reduction of electron-deficient alkenes and carbonyl compounds is described. UVA irradiations of substituted maleimides with dispersions of titania (Aeroxide P25) in methanol/acetonitrile (1:9) solvent under dry anoxic conditions led to hydrogenation and production of the corresponding succinimides. Aromatic and heteroaromatic aldehydes were reduced to primary alcohols in similar titania photocatalyzed reactions. A mechanism is proposed which involves two proton-coupled electron transfers to the substrates at the titania surface.
- Manley, David W.,Buzzetti, Luca,MacKessack-Leitch, Andrew,Walton, John C.
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p. 15324 - 15338
(2015/01/16)
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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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- The scalable pinacol coupling reaction utilizing the inorganic electride [Ca2N]+·e- as an electron donor
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The scalable pinacol coupling reaction is realized utilizing the inorganic electride [Ca2N]+·e- as an electron donor in organic solvents. The bond cleavages of the [Ca2N] + layers by methanol play a vital role in transferring anionic electrons to electrophilic aldehydes, accompanying the formation of Ca(OMe) 2 and ammonia. The Royal Society of Chemistry 2014.
- Kim, Ye Ji,Kim, Sun Min,Hosono, Hideo,Yang, Jung Woon,Kim, Sung Wng
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supporting information
p. 4791 - 4794
(2014/05/06)
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- Alkaloid induced enantioselective electroreduction of acetophenone
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The feasibility of the enantioselective electroreduction of pro-chiral acetophenone was investigated at the silver cathode in an undivided cell for the first time. Electroreduction of acetophenone in the presence of cinchonidine (CD) yielded two main products: the optically active alcohol, and the dimer product pinacol with no optical rotation. The influence of water in the co-solvent (MeCN/H2O), supporting electrolyte, electrode material, current density, and the alkaloid type on the enantiomeric excesses (ee) and yield was investigated. Under the optimized conditions, the alcohol was obtained with a 21.6% ee and a 3.6% yield, whereas, an 83.2% yield and a 5.5 dl/meso ratio were obtained for pinacol. The electrochemical behavior of the samples was also studied through cyclic voltammetry (CV). Finally, we proposed a possible induction mechanism based on the results of the electrolysis and CV.
- Chen, Bao-Li,Xiao, Yan,Xu, Xiao-Ming,Yang, Heng-Pan,Wang, Huan,Lu, Jia-Xing
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p. 320 - 326
(2013/10/01)
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- Use of electrochemistry to provide efficient SmI2 catalytic system for coupling reactions.
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Samarium metal has been used for the first time as electrode material to perform as an efficient and versatile SmI2 catalytic system assisted by electrochemistry. The established electrocatalytic procedure that excludes any metal additives was successfully applied in various transformations mediated by this useful reagent.
- Sun, Linhao,Sahloul, Kamar,Mellah, Mohamed
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p. 2568 - 2573
(2013/11/19)
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- A samarium "soluble" anode: A new source of SmI2 reagent for electrosynthetic application
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An electrochemical method to prepare solutions of samarium diiodide in THF is reported. The simple electrolysis of a samarium rod provides a rapid and straightforward in situ synthesis of SmI2. The electrogenerated complex catalyzes various C-C bond formations. The reagent is produced continuously (see scheme) and leads to efficient organic electrosynthesis with significantly smaller amounts of solvent than usually required. Copyright
- Sahloul, Kamar,Sun, Linhao,Requet, Alexandre,Chahine, Youhana,Mellah, Mohamed
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supporting information
p. 11205 - 11209,5
(2012/12/11)
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- A samarium "soluble" anode: A new source of SmI2 reagent for electrosynthetic application
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An electrochemical method to prepare solutions of samarium diiodide in THF is reported. The simple electrolysis of a samarium rod provides a rapid and straightforward in situ synthesis of SmI2. The electrogenerated complex catalyzes various C-C bond formations. The reagent is produced continuously (see scheme) and leads to efficient organic electrosynthesis with significantly smaller amounts of solvent than usually required. Copyright
- Sahloul, Kamar,Sun, Linhao,Requet, Alexandre,Chahine, Youhana,Mellah, Mohamed
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supporting information
p. 11205 - 11209
(2013/01/14)
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- Reductive coupling of carbonyl compounds promoted by cobalt or titanium nanoparticles
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The reaction of a series of aldehydes and ketones with readily prepared cobalt or titanium nanoparticles, under mild reaction conditions, led to the obtention of different reductive dimerization products depending on the nature of the transition metal used. Cobalt nanoparticles (CoNPs) allowed the selective transformation of the starting carbonyl compounds into vicinal diols, whereas the reaction promoted by titanium nanoparticles (TiNPs) led to the formation of the corresponding alkenes. In this last case, the use of trimethylsilyl chloride (TMSCl) as additive, at 0 °C, also allowed the obtention of vicinal diols after acidic aqueous work-up. ARKAT-USA, Inc.
- Nador, Fabiana,Mascaro, Evangelina,Castro, Melisa,Vitale, Cristian,Radivoy, Gabriel
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experimental part
p. 312 - 326
(2011/06/17)
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- Study on improved diastereoselectivity in photo-induced electron transfer pinacol coupling reactions of substituted acetophenones
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Novel diastereoselective photo-induced pinacol coupling reactions of acetophenones by using triethylamine and chiral tertiary amines as electron donating co-sensitizers were studied. Various influence factors including solvents, substituents, and chiral a
- Ma, Nan,Shi, Wei,Zhang, Ronghua,Zhu, Zhiliang,Jiang, Zhiqin
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experimental part
p. 718 - 720
(2011/03/20)
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- Iron-catalyzed pinacol coupling of aryl ketones with a phenyltitanium reagent: A new type of catalytic reaction
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A reaction of aryl ketones with phenyltitanium triisopropoxide ([PhTi(Oi-Pr)3]) in the presence of [Fe(acac)3] as a catalyst (1 mol%) gave the corresponding pinacols in high yields. The catalytic cycle of this process involves an iron-catalyzed disproportionation of [PhTi(Oi-Pr) 3] into biphenyl and a lowvalent titanium species.
- Hayashi, Tamio,Sasaki, Keigo
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supporting information; experimental part
p. 492 - 494
(2011/06/25)
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- Mechanistic study of half-titanocene-based reductive pinacol coupling reaction
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The reductive pinacol coupling reaction of aldehydes or ketones creating a new C-C bond has been a major tool to produce 1,2-diol compounds. The reaction mechanism is known to be composed of sequential three steps (activation, coupling, and dissociation). In this work, we studied the dissociation step of half-titanocene-based catalytic systems. Cp and Cp* derivatives of the pinacolato-bridged dinuclear complex were synthesized and evaluated as possible models for intermediates from the coupling step. We monitored 1H-NMR spectra of the reaction between the metalla-pinacol intermediates and D2O. New reaction routes of the dissociation step including oxo- and pinacolato-dibridged dinuclear complexes and oxo-bridged multinuclear complexes have been suggested. Copyright
- Kim, Youngjo,Do, Youngkyu,Park, Sungjin
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experimental part
p. 3973 - 3978
(2012/03/26)
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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 new Yb3+-catalyzed pinacol and imine-coupling reaction
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Ytterbium triflate, Yb(OTf)3, catalyzes the intermolecular reductive homocouplings of imines, aldehydes, and ketones at loadings of 5 mol % in the presence of Mg and Me3SiCl to give isolated yields of up to 95%. Diastereoselectivity of up to 4/96 (dl/meso) is achieved for aromatic aldehydes, up to 100% dl for aliphatic aldehydes, and 100% dl for an intramolecular imine coupling.
- Aspinall, Helen C.,Greeves, Nicholas,Hin, Shane Lo Fan
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experimental part
p. 1558 - 1561
(2010/06/13)
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- Unexpected TiIII/Mn-promoted pinacol coupling of ketones
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Titanocene(III) chemistry has emerged in the last decades as an indispensable tool in C-C bond-forming reactions. In this context, pinacol and related reactions allow the stereoselective synthesis of vicinal diols. In this work, we present new applications of these reactions using as starting materials aromatic ketones. Simple and smooth reaction conditions have been developed and have been applied for inter- and intramolecular processes. We also describe that although Cp2TiCl is usually used as a monoelectronic reducing agent, it can be also used as an efficient Lewis acid.
- Paradas, Miguel,Campana, Araceli G.,Estevez, Rosa E.,De Cienfuegos, Luis Alvarez,Jimenez, Tania,Robles, Rafael,Cuerva, Juan M.,Oltra, J. Enrique
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experimental part
p. 3616 - 3619
(2009/09/06)
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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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- 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)
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- 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)
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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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- Geometry determination of tetrasubstituted stilbenes by proton NMR spectroscopy
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A simple spectroscopic method was applied to determine the geometry of tetrasubstituted alkenes. The observation of the 5J-coupling constants in proton NMR spectra on the 13C satellite signals could confirm the previous misassignment of 2,3-diphenylbutene. Hence, the (E)-isomer showed a 1.5 Hz coupling constant, whereas the (Z)-isomer showed a 1.1 Hz coupling constant. Based on this new assignment and a stereospecific preparation, we also propose a revision concerning the NMR data of 2,3-diphenyl-2,3-butanediol.
- Fluxá, Viviana S.,Jenny, Titus A.,Bochet, Christian G.
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p. 3793 - 3795
(2007/10/03)
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- Samarium diiodide-catalyzed diastereoselective pinacol couplings
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(Chemical Equation Presented) A complex of samarium diiodide (Sml 2) with tetraglyme catalyzes the intermolecular pinacol coupling of aromatic or aliphatic aldehydes at loadings of 10 mol % in the presence of Me2SiCl2 and Mg. Diastereoselectivity of up to 95/5 (±/meso) has been achieved for aliphatic aldehydes and up to 19/81 (±/meso) for aromatic aldehydes. De values of up to 99% have been achieved in intramolecular pinacol coupling reactions using the Sml 2/tetraglyme/Mg/Me2SiCl2 catalytic system.
- Aspinall, Helen C.,Greeves, Nicholas,Valla, Carine
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p. 1919 - 1922
(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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- Ultrasound-promoted magnesium-ammonium bromide-mediated pinacol coupling of aromatic aldehydes and ketones
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Pinacol coupling of aromatic aldehydes and ketones by Mg powder in 0.1-mol/L ammonium bromide aqueous solution can lead to the corresponding pinacols in 22-90% yields within 1-3 h at rt under ultrasound irradiation. Copyright Taylor & Francis, Inc.
- Li, Ji-Tai,Chen, Yan-Xue,Li, Tong-Shuang
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p. 2831 - 2837
(2007/10/03)
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- Synthesis of α,β-unsaturated dioxanes, dioxolanes and dioxepanes by trans-acetalisation of dimethylacetals with meso or C 2-symmetrical 1,2-, 1,3- and 1,4-diols
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Several o-dibenzylic diols were prepared reacting organometallics with o-phthalaldehyde at room temperature in ether. The identity of the meso and C2-symmetrical (D,L) isomers as well as their ratio were determined by chiral gas chromatography. The meso and C2 (racemic) stereoisomeric diols were easily separated by flash chromatography on silica gel. A set of 18 α,β-unsaturated acetals were then prepared reacting those, as well as commercially available 1,2, 1,3 and 1,4 diols, with the corresponding methylacetals in acidic medium. A trans-acetalisation procedure adapted to the cases of fragile allylic alcohols or unfavorable 1,6 diols-derived dioxonanes based on a Dean-Stark trapping of methanol was also employed.
- Lemiègre, Lo?c,Lesetre, Fleur,Combret, Jean-Claude,Maddaluno, Jacques
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p. 415 - 427
(2007/10/03)
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- Magnesium-induced pinacol coupling of aromatic aldehydes and ketones in water under ultrasound
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The pinacol coupling of aromatic aldehydes and ketones has been carried out in 20-62% and 10-91% yields, respectively with Mg and Mg-MgCl2 in water under ultrasound irradiation at room temperature for 3-4hr.
- Li, Ji-Tai,Bian, Yan-Jiang,Liu, Shu-Ming,Li, Tong-Shuang
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p. 196 - 198
(2007/10/03)
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- A highly diastereoselective pinacol coupling reaction of aldehydes and ketones using low-valence niobium generated from Nb(V)
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A simple method for the diastereoselective synthesis of racemic 1,2-diol mediated by low-valence niobium generated in situ is described. A 1,4-dioxane-toluene solvent system was found to be essential to achieve higher selectivities and to prevent other reactions of pinacols, such as deoxygenation and acetal formation. Aromatic aldehydes and ketones were converted to the corresponding pinacols with up to 97 and 85% de, respectively.
- Arai, Shigeru,Sudo, Yukinori,Nishida, Atsushi
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p. 287 - 288
(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.
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- Titanium-mediated carboxylation of alkynes with carbon dioxide
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The regioselective carboxylation of nonactivated internal alkynes can be performed with carbon dioxide under atmospheric pressure using a simple procedure based on the chemistry of Sato-type diisopropyloxytitanacyclopropenes. Various polysubstituted vinylcarboxylic acids and butenolides can be prepared in this way. In addition, this paper describes an experimental protocol for the preparation of solutions of (η2-cyclopentene)diisopropyloxytitanium. This complex also reacts with carbon dioxide, and mediates pinacol coupling of acetophenone. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Six, Yvan
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p. 1157 - 1171
(2007/10/03)
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- A novel, solventless reductive coupling of carbonyl compounds by alkali metals, catalysed by bromobenzene
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Catalysed by bromobenzene, alkali metals including Li, Na, and K can mediate the reductive coupling of carbonyl compounds under mild, solventless conditions to furnish the corresponding pinacol products.
- Zhao, Hui,Li, De-Jin,Deng, Lan,Liu, Lei,Guo, Qing-Xiang
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p. 506 - 507
(2007/10/03)
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- Pinacol coupling of aromatic aldehydes and ketones using Zn-ZnCl2 under ultrasound
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The coupling reaction of aromatic aldehydes and ketones leading to pinacols has been carried out using Zn-ZnCl2 in 50% aq. THF under ultrasound in 5-77% yield.
- Zang, Hong-Jun,Li, Ji-Tai,Ning, Ning,Wei, Na,Li, Tong-Shuang
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p. 1078 - 1080
(2007/10/03)
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- Reactions of 1,2-diketones with vinyllithium: Addition reactions and dianionic oxy Cope rearrangements of cyclic and acyclic substrates
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Dianionic oxy Cope rearrangements have been shown to take place at low temperature upon syn double addition of alkenyllithium derivatives to cyclobutanedione compounds such as benzocyclobutenedione chromium complex 1 or squaric acid esters. In order to obtain some insight into the more general applicability of this type of reaction sequence beyond these special cases, a number of 1,2-diketones were treated with vinyllithium. The diketones tested include benzil derivatives, aliphatic acyclic 1,2-diketones, ortho-quinones, and cyclic aliphatic 1,2-diketones. With benzil and heterobenzil derivatives, the desired double addition/dianionic oxy Cope rearrangement was found to take place at low temperature, leading to 1,6-diketones and their intramolecular aldol adducts in up to 80% overall yield. With acyclic aliphatic 1,2-diketones as substrates, this reaction sequence was also found, albeit with somewhat lower yields and requiring higher temperatures than in the benzil cases. A brief investigation of the intramolecular aldol adduct/1,6-hexanedione equilibrium indicated that the preferential formation of intramolecular aldol adducts at lower temperatures and at shorter reaction times appears to be the result of kinetic reaction control, whereas the preference for 1,6-diketones at higher temperatures is caused by thermodynamic reaction control, ortho-Quinones reacted with vinyllithium only by addition; no dianionic oxy Cope rearrangement was observed. This was also the case for most aliphatic cyclic diketones; however, in the case of 1,2-indanedione, rearrangement products were obtained in moderate yield at elevated reaction temperatures.
- Clausen, Christian,Wartchow, Rudolf,Butenschoen, Holger
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- Generation of reactive low-valent titanium species using metal-arenes as efficient organic reductants for TiCl3: Applications to organic synthesis
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A comprehensive study on the use of metal-arene systems as organic reductants for TiCl3 has resulted in an efficient method for the generation of highly reactive low-valent titanium (LVT) reagents. The activated titanium species could be prepared by refluxing a mixture of substoichiometric amounts of arenes, TiCl3, and Li/Mg in THF or DME. Among the LVT reagents screened, TiCl3 - Li-naphthalene - THF (reagent I) was the best for coupling of carbonyls to olefins. The reagent could carry out the McMurry olefination of both aromatic and aliphatic substrates at a lower temperature and in a much reduced time as compared to the conventional procedures. Subtle changes in the method of preparation of the LVT reagents influenced the stereoisomeric ratio of the olefins. The reagent was also useful for the synthesis of O- and N- heterocycles and vicinal diamines via intramolecular carbonyl coupling and reductive duplication of imines, respectively.
- Rele,Talukdar,Banerji,Chattopadhyay
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p. 2990 - 2994
(2007/10/03)
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- Indium-catalyzed reductive coupling of aromatic carbonyl compounds and imines in the presence of aluminum and chlorosilanes
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Reductive homocoupling of aromatic aldehydes, ketones, and imines has been achieved in tetrahydrofuran (THF) at room temperature using a catalytic amount of InCl3 (0.5-3.0 mol %) under a nitrogen atmosphere in the presence of chlorotrimethylsilane (TMSCl) and aluminum metal (Al) to provide the corresponding 1,2-diols and 1,2-diamines, respectively, in good to moderate yields. Other indium compounds such as In(NO3)3, cyclopentadienylindium, and indium metal have also been revealed to be effective as catalysts. The catalytic effect of the indium compound is remarkable, and, thus, without it, no reaction occurs in the case of aromatic aldehydes and aldimines, and an induction period is quite long in the case of aromatic ketones. Without either TMSCl or Al, no reaction proceeds even in the presence of the catalyst. Unfortunately, the diastereoselectivity of the products (dl and meso) is not high. Although the precise reaction scheme is not yet clear, we tentatively propose that a redox-active In-Al alloy might be formed on the surface of aluminum in the presence of TMSCl, and an electron transfer from the alloy to substrate might occur.
- Ohtaka, Seiji
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p. 309 - 316
(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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