- Direct Hydrodecarboxylation of Aliphatic Carboxylic Acids: Metal- and Light-Free
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A mild and inexpensive method for direct hydrodecarboxylation of aliphatic carboxylic acids has been developed. The reaction does not require metals, light, or catalysts, rendering the protocol operationally simple, easy to scale, and more sustainable. Crucially, no additional H atom source is required in most cases, while a broad substrate scope and functional group tolerance are observed.
- Burns, David J.,Lee, Ai-Lan,McLean, Euan B.,Mooney, David T.
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supporting information
p. 686 - 691
(2022/01/28)
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- Reactions of benzyltriphenylphosphonium salts under photoredox catalysis
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The development of benzyltriphenylphosphonium salts as alkyl radical precursors using photoredox catalysis is described. Depending on substituents, the benzylic radicals may couple to form C-C bonds or abstract a hydrogen atom to form C-H bonds. A natural product, brittonin A, was also synthesized using this method.
- Boldt, Andrew M.,Dickinson, Sidney I.,Ramirez, Jonathan R.,Benz-Weeden, Anna M.,Wilson, David S.,Stevenson, Susan M.
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supporting information
p. 7810 - 7815
(2021/09/28)
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- Metal-Free Heterogeneous Semiconductor for Visible-Light Photocatalytic Decarboxylation of Carboxylic Acids
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A suitable protocol for the photocatalytic decarboxylation of carboxylic acids was developed with metal-free ceramic boron carbon nitrides (BCN). With visible light irradiation, BCN oxidize carboxylic acids to give carbon-centered radicals, which were trapped by hydrogen atom donors or employed in the construction of the carbon-carbon bond. In this system, both (hetero)aromatic and aliphatic acids proceed the decarboxylation smoothly, and C-H, C-D, and C-C bonds are formed in moderate to high yields (35 examples, yield up to 93%). Control experiments support a radical process, and isotopic experiments show that methanol is employed as the hydrogen atom donor. Recycle tests and gram-scale reaction elucidate the practicability of the heterogeneous ceramic BCN photoredox system. It provides an alternative to homogeneous catalysts in the valuable carbon radical intermediates formation. Moreover, the metal-free system is also applicable to late-stage functionalization of anti-inflammatory drugs, such as naproxen and ibuprofen, which enrich the chemical toolbox.
- Shi, Jiale,Yuan, Tao,Zheng, Meifang,Wang, Xinchen
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p. 3040 - 3047
(2021/03/09)
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- Molybdenum-Catalyzed Deoxygenation Coupling of Lignin-Derived Alcohols for Functionalized Bibenzyl Chemicals
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With the growing demand for sustainability and reducing CO2 footprint, lignocellulosic biomass has attracted much attention as a renewable, carbon-neutral and low-cost feedstock for the production of chemicals and fuels. To realize efficient utilization of biomass resource, it is essential to selectively alter the high degree of oxygen functionality of biomass-derivates. Herein, we introduced a novel procedure to transform renewable lignin-derived alcohols to various functionalized bibenzyl chemicals. This strategy relied on a short deoxygenation coupling pathway with economical molybdenum catalyst. A well-designed H-donor experiment was performed to investigate the mechanism of this Mo-catalyzed process. It was proven that benzyl carbon-radical was the most possible intermediate to form the bibenzyl products. It was also discovered that the para methoxy and phenolic hydroxyl groups could stabilize the corresponding radical intermediates and then facilitate to selectively obtain bibenzyl products. Our research provides a promising application to produce functionalized aromatics from biomass-derived materials.
- Jiang, Huifang,Lu, Rui,Luo, Xiaolin,Si, Xiaoqin,Xu, Jie,Lu, Fang
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supporting information
p. 1292 - 1296
(2020/12/09)
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- Exhaustive Reduction of Esters Enabled by Nickel Catalysis
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We report a one-step procedure to directly reduce unactivated aryl esters into their corresponding tolyl derivatives. This is achieved by an organosilane-mediated ester hydrosilylation reaction and subsequent Ni/NHC-catalyzed hydrogenolysis. The resulting conditions provide a direct and efficient alternative to multi-step procedures for this transformation that often require the use of hazardous metal hydrides. Applications in the synthesis of -CD3-containing products, derivatization of bioactive molecules, and chemoselective reduction in the presence of other C-O bonds are demonstrated.
- Cook, Adam,Prakash, Sekar,Zheng, Yan-Long,Newman, Stephen G.
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supporting information
p. 8109 - 8115
(2020/05/20)
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- Hydrogenation of plant polyalkoxybenzene derivatives: convenient access to coenzyme Q0 analogues
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A technologically advanced protocol has been developed for converting plant allyl(polyalkoxy)benzenes to methyl- and propyl(polyalkoxy)benzenes being intermediates in the syntheses of coenzyme Q0 analogues. The key stage of allyl and benzaldehyde moieties hydrogenation was carried out in a periodical autoclave mode on highly porous ceramic block Pd-catalysts. These catalysts possess large surface area, low hydraulic resistance, significant thermal and mechanical stabililty, multiple cycling and easy regeneration, which can dramatically reduce Pd consumption.
- Khrustalev, Victor N.,Muravsky, Egor A.,Semenov, Victor V.,Shinkarev, Ilia Yu.,Varakutin, Alexander E.
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p. 599 - 601
(2020/10/18)
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- Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the in Situ Methylation of Tertiary Amines
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Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp3-Csp3 bonds. We demonstrate PO(OMe)3 (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: The in situ methylation of tertiary amines by PO(OMe)3, Ni-catalyzed C-N bond cleavage, and concurrent Csp3-Csp3 bond formation.
- Nwachukwu, Chideraa Iheanyi,McFadden, Timothy Patrick,Roberts, Andrew George
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p. 9979 - 9992
(2020/09/03)
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- Nickel-catalyzed intelligent reductive transformation of the aldehyde group using hydrogen
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The selective transformation of the aldehyde group (-CHO) in multifunctional oxygenates is a key challenge in the development of sustainable biomass feedstock. Herein, a smart Ni-MFC catalyst was developed from a 2D Ni-based metal-organic framework (MOF), which efficiently promoted the transformation of -CHO in the presence of H2 to a methyl group (-CH3) via the reductive etherification and hydrogenolysis of the C-O ether bond in methanol. Moreover, the catalytic process could be controlled to directionally produce methyl ether (-CH2OR) using the reductive etherification protocol. For the catalytic reduction of vanillin, the Ni-MFC-700 catalyst guaranteed the full conversion of vanillin and 96.5% yield of the desired 2-methoxy-4-methylphenol (MMP), while the Ni-MFC-500 catalyst afforded about 82.7% yield of 4-(methoxymethyl)-2-methoxyphenol in methanol solvent. This is a novel and promising approach for the valorization of multifunctional oxygenates and biomass-derived platform compounds.
- Tong, Xinli,Guo, Pengfei,Liao, Shengyun,Xue, Song,Zhang, Haigang
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p. 5828 - 5840
(2019/11/11)
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- Palladium-Catalyzed Methylation of Aryl, Heteroaryl, and Vinyl Boronate Esters
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A method for the direct methylation of aryl, heteroaryl, and vinyl boronate esters is reported, involving the reaction of iodomethane with aryl-, heteroaryl-, and vinylboronate esters catalyzed by palladium and PtBu2Me. This transformation occurs with a remarkably broad scope and is suitable for late-stage derivatization of biologically active compounds via the boronate esters. The unique capabilities of this method are demonstrated by combining carbon-boron bond-forming reactions with palladium-catalyzed methylation in a tandem transformation.
- Haydl, Alexander M.,Hartwig, John F.
-
supporting information
p. 1337 - 1341
(2019/02/26)
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- Difluoromethylthiolation of Phenols and Related Compounds with a HF2CSO2Na/Ph2PCl/Me3SiCl System
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A novel HF2CSO2Na/Ph2PCl/Me3SiCl system is disclosed for the late-stage direct difluoromethylthiolation of Csp2 and Csp3 nucleophiles. Difluoromethylthiolation of phenols and naphthols proceeded nicely under this system to regioselectively provide corresponding SCF2H compounds in good yields. Other substrates such as indoles, pyrroles, pyrazoles, enamines, ketones, and β-keto esters were also transformed to corresponding SCF2H products in good yields. The late-stage direct difluoromethylthiolation of a number of natural products and pharmaceutically attractive molecules was also achieved.
- Huang, Zhongyan,Matsubara, Okiya,Jia, Shichong,Tokunaga, Etsuko,Shibata, Norio
-
supporting information
p. 934 - 937
(2017/02/26)
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- Nickel-catalyzed methylation of aryl halides/tosylates with methyl tosylate
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This work describes the cross-electrophile methylation of aryl bromides and aryl tosylates with methyl tosylate. The mild reaction conditions allow effective methylation of a wide set of heteroaryl electrophiles and dimethylation of dibromoarenes.
- Wang, Jiawang,Zhao, Jianhong,Gong, Hegui
-
supporting information
p. 10180 - 10183
(2017/09/23)
-
- Efficient synthesis and antioxidant activities of N-heterocyclyl substituted Coenzyme Q analogues
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A new strategy for the efficient synthesis of C-5 heterocyclyl substituted Coenzyme Q analogues was developed by N-alkylation of bromomethylated quinone 11 with a series of amines 12 under metal-free conditions. In vitro antioxidant activities of these Coenzyme Q analogues were evaluated and compared with commercial antioxidant Coenzyme Q10 by employing DPPH assay. All these N-heterocyclyl substituted Coenzyme Q analogues are found to be exhibiting good antioxidant properties and may be used as potent antioxidants for combating oxidative stress.
- Wang, Jin,Xia, Fei,Jin, Wen-Bin,Guan, Jin-Yan,Zhao, Hang
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p. 214 - 218
(2016/08/25)
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- Tandem catalytic depolymerization of lignin by water-tolerant Lewis acids and rhodium complexes
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Lignin is an attractive renewable feedstock for aromatic bulk and fine chemicals production, provided that suitable depolymerization procedures are developed. Here, we describe a tandem catalysis strategy for ether linkage cleavage within lignin, involving ether hydrolysis by water-tolerant Lewis acids followed by aldehyde decarbonylation by a Rh complex. In situ decarbonylation of the reactive aldehydes limits loss of monomers by recondensation, a major issue in acid-catalyzed lignin depolymerization. Rate of hydrolysis and decarbonylation were matched using lignin model compounds, allowing the method to be successfully applied to softwood, hardwood, and herbaceous dioxasolv lignins, as well as poplar sawdust, to give the anticipated decarbonylation products and, rather surprisingly, 4-(1-propenyl)phenols. Promisingly, product selectivity can be tuned by variation of the Lewis-acid strength and lignin source.
- Jastrzebski, Robin,Constant, Sandra,Lancefield, Christopher S.,Westwood, Nicholas J.,Weckhuysen, Bert M.,Bruijnincx, Pieter C.A.
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p. 2074 - 2079
(2017/07/25)
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- Highly chemoselective hydrogenation of active benzaldehydes to benzyl alcohols catalyzed by bimetallic nanoparticles
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By using novel Pd/Ni bimetallic nanoparticles as a catalyst, the active benzaldehydes were hydrogenated to the corresponding benzyl alcohols as unique products in practical quantitative yields. The undesired catalytic hydrogenolysis of the benzyl alcohol was inhibited completely. By using this hydrogenation as a key step, the total synthesis of the natural product gastrodin was achieved with less total steps and a higher total yield.
- Liu, Chulong,Bao, Hailin,Wang, Dingsheng,Wang, Xinyan,Li, Yadong,Hu, Yuefei
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p. 6460 - 6462
(2015/11/16)
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- Homocoupling versus reduction of radicals: An experimental and theoretical study of Ti(iii)-mediated deoxygenation of activated alcohols
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A detailed experimental and theoretical study corroborates that the reductive deoxygenation of activated (allylic or benzylic) alcohols with excess Ti(iii) proceeds via an allyl(benzyl)-radical and allyl(benzyl)-Ti, which is protonated, regioselectively in the case of allylic derivatives. The H atom of the newly formed C-H bond in the product originates from the -OH group of the starting material. The deoxygenation of lithium alkoxides or alcohols by using 1.0 mol of Ti(iii) leads to the corresponding dimerization products in good yields. An excellent agreement with the experimental data was obtained by using a reaction kinetics simulator to discriminate between competing reactions.
- Prieto, Consuelo,González Delgado, José A.,Arteaga, Jesús F.,Jaraíz, Martín,López-Pérez, José L.,Barrero, Alejandro F.
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p. 3462 - 3469
(2015/03/18)
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- Hydrogenation of aromatic aldehydes to aromatic hydrocarbons over Cu-HZSM-5 catalyst
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With benzaldehyde as a model compound, the hydrogenation of aromatic aldehydes to aromatic hydrocarbons was investigated. Cu-HZSM-5 exhibited excellent catalytic performance for the reaction. The obtained catalysts were characterized by N2 adsorption/desorption, N2O chemisorptions, X-ray diffraction, NH3-temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that Cu 0 active species exhibited poor activity for the hydrogenation of benzene ring, while the strong acidity of HZSM-5 accelerated the hydrogenation reaction via hydrogen spillover phenomenon and the C-O activation effect. In addition, the catalyst was proved to be effective for the hydrogenation of a series of aromatic aldehydes to corresponding aromatic hydrocarbons.
- Kong, Xiangjin,Chen, Ligong
-
-
- Efficient palladium-catalyzed C-O hydrogenolysis of benzylic alcohols and aromatic ketones with polymethylhydrosiloxane
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A simple method has been developed for the reductive deoxygenation of aromatic ketones and benzylic alcohols in the presence of polymethylhydrosiloxane (PMHS). The reductive deoxygenation of aromatic ketones and benzylic alcohols, including secondary alcohols, to the corresponding methylene hydrocarbons has been achieved in good to excellent yields using palladium chloride (PdCl2) as catalyst and PMHS as hydride source. Such deoxygenations were successfully with aryl alkyl ketones and diaryl ketones, as exemplified by the reductive deoxygenation of acetophenone and benzopheneone, respectively. The corresponding benzylic alcohols and secondary alcohol analogues could also be converted into their respective methylene hydrocarbons by the PdCl2/PMHS system.
- Wang, Hu,Li, Li,Bai, Xing-Feng,Shang, Jun-Yan,Yang, Ke-Fang,Xu, Li-Wen
-
supporting information
p. 341 - 347
(2013/05/08)
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- One-by-one hydrogenation, cross-coupling reaction, and Knoevenagel condensations catalyzed by PdCl2 and the downstream palladium residue
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A novel catalyst-economic strategy with a recovered palladium catalyst was successfully applied for multi-task and maximum reuse in different types of one-by-one downstream reactions, from catalytic hydrogenation to Suzuki and Sonogashira-type cross-coupling reactions, Knoevenagel condensations, and trans-Knoevenagel-like condensations.
- Wang, Hu,Li, Li,Bai, Xing-Feng,Deng, Wen-Hui,Zheng, Zhan-Jiang,Yang, Ke-Fang,Xu, Li-Wen
-
supporting information
p. 2349 - 2355
(2013/09/12)
-
- Metal-free reductive cleavage of benzylic esters and ethers: Fragmentations result from single and double electron transfers
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The mechanisms for the reductive cleavage of benzylic esters and ethers by neutral organic electron donor 1 are different (see scheme). Products isolated from the cleavage of benzylic ethers result from the transfer of two electrons, without the intermediacy of benzyl radicals, which are believed to be intermediates in the reductive cleavage of benzylic esters. Copyright
- Doni, Eswararao,O'Sullivan, Steven,Murphy, John A.
-
supporting information
p. 2239 - 2242
(2013/03/28)
-
- Directed metalation?£?cross-coupling strategies. Total syntheses of the alleged and the revised phenanthrene natural product gymnopusin
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The total synthesis of gymnopusin (2) is described. The originally assigned structure for gymnopusin 1a was found to be incorrect by total synthesis using the Directed ortho-Metalation (DoM)?£?Cross- Coupling?£?Directed remote Metalation (DreM) sequence, a demonstrable key strategy for the regioselective construction of the 9-phenanthrol core. The revised structure of gymnopusin (2) was confirmed by synthesis by adopting the same strategy but involving a key remote anionic Fries-rearrangement step. Both routes highlight methodologies and concepts which may be of value in the regiocontrolled synthesis of phenanthrenoids specifically and in complex polycyclic aromatics in general. Copyright
- Wang, Xin,Fu, Jian-Min,Snieckus, Victor
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p. 2680 - 2694
(2013/03/13)
-
- A green and efficient synthesis of 1-chloromethyl -2,3,4,5-tetramethoxy6- methylbenzene
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The title compound, a key intermediate for preparing coenzyme Q analogues, was prepared in excellent yield by a reaction sequence starting from the commercially available 3,4,5-trlmethoxybenzadehyde via Wolff-Kishner reduction, selective bromination, methoxylation and Blanc chloromethylation reaction.
- Wang, Jin,Yang, Jian,Yang, Bo,Hu, Xiao,Sun, Jia-Qiang,Yang, Tao
-
experimental part
p. 717 - 718
(2011/04/22)
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- Alternative synthesis of 5-chloromethyl-2,3-dimethoxy-6-methyl-1, 4-benzoquinone: A key intermediate for preparing coenzyme Q analogues
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The title compound, a key intermediate for preparing Coenzyme Qn family, was prepared in high yield by a reaction sequence starting from the commercially available 3, 4, 5-trimethoxy-benzadehyde via Wolff-Kishner reduction, Vilsmeier-Haack reaction, Blanc chloromethylation reaction, Dakin reaction and oxidation.
- Wang, Jin,Yang, Jian,Yang, Bo,Sun, Jia-Qiang,Yang, Tao
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experimental part
p. 724 - 725
(2011/04/24)
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- Weakening C-O bonds: Ti(III), a new reagent for alcohol deoxygenation and carbonyl coupling olefination
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Investigations detailed herein, including density functional theory (DFT) calculations, demonstrate that the formation of either alkoxy- or hydroxy-Ti(III) complexes considerably decreases the energy of activation for C-O bond homolysis. As a consequence of this observation, we described two new synthetic applications of Nugent's reagent in organic chemistry. The first of these applications is an one-step methodology for deoxygenation-reduction of alcohols, including benzylic and allylic alcohols and 1,2-dihydroxy compounds. Additionally, we have also proved that Ti(III) is capable of mediating carbonyl coupling-olefination. In this sense, and despite the fact that for over 35 years it has been widely accepted that either Ti(II) or Ti(0) was the active species in the reductive process of the McMurry reaction, the mechanistic evidence presented proves the involvement of Ti(III) pinacolates in the deoxygenation step of the herein described Nugent's reagent-mediated McMurry olefination. This observation sheds some light on probably one of the mechanistically more complex transformations in organic chemistry. Finally, we have also proved that both of these processes can be performed catalytically in Cp 2TiCl2 by using trimethylsilyl chloride (TMSCl) as the final oxygen trap.
- Dieguez, Horacio R.,Lopez, Armando,Domingo, Victoriano,Arteaga, Jesus F.,Dobado, Jose A.,Herrador, M. Mar,Quilez Del Moral, Jose F.,Barrero, Alejandro F.
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supporting information; experimental part
p. 254 - 259
(2010/03/25)
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- A versatile catalyst system for suzuki-miyaura cross-coupling reactions of C(sp2)-tosylates and mesylates
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Figure Presented A catalyst system for the Suzuki-Miyaura cross-coupling reactions of aryl and vinyl tosylates and mesylates has been developed. This catalyst displays excellent functional group tolerance and allows the coupling of heteroarylboronic acids
- Bhayana, Brijesh,Fors, Brett P.,Buchwald, Stephen L.
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supporting information; experimental part
p. 3954 - 3957
(2009/12/03)
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- Self-modulated highly chemoselective direct-reductive-amination (DRA) of benzaldehydes straightforward to N-monosubstituted benzylamine hydrochlorides
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An unprecedented efficient and chemoselective DRA of benzaldehydes and primary amines was developed to directly yield N-monosubstituted benzylamine hydrochlorides as single products in practically quantitative yields. The method was characterized by simply adding a few milliliters of CHCl3 in the conventional Pd-C catalytic hydrogenation system at atmospheric pressure and room temperature. A self-modulated system and a four-stage cyclic pathway were proposed.
- Xing, Lixin,Cheng, Chuanjie,Zhu, Rui,Zhang, Boyang,Wang, Xinyan,Hu, Yuefei
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supporting information; experimental part
p. 11783 - 11788
(2009/04/05)
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- A solvent-controlled highly efficient Pd-C catalyzed hydrogenolysis of benzaldehydes to methylbenzenes via a novel 'acetal pathway'
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Pd-C catalyzed hydrogenolysis of benzaldehydes to methylbenzenes has been described to proceed via a 'benzenemethanol pathway'. In this article, a novel 'acetal pathway' was first revealed by a systematic study when lower alcohols were used as solvents and a solvent-controlled highly efficient procedure was established.
- Xing, Lixin,Wang, Xinyan,Cheng, Chuanjie,Zhu, Rui,Liu, Bo,Hu, Yuefei
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p. 9382 - 9386
(2008/02/10)
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- Method for producing toluol derivatives
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A process for preparing toluene derivatives of the formula I, where R1, R2 and R3 independently of one another are hydrogen, halogen, C1–C6-alkyl, hydroxyl or C1–C6-alkoxy, by hydrogenating benzaldehydes and/or benzyl alcohols of the formula II, with hydrogen in the presence of a catalyst, which is described in more detail in the description.
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Page/Page column 7
(2008/06/13)
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- Ion pairing effects on the regioselectivity of arylic versus benzylic C-O bond reductive cleavage: synthetic applications
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The regioselectivity of the reductive cleavage of 3,4,5-trimethoxybenzyl methyl ether strongly depends on the alkali metal employed as a reducing agent and solvent effects. Reactions run using Na as a reducing agent led to aromatic C(4)-O bond cleavage, whilst reductions run in the presence of Na/15-crown-5, or using Li as a reducing agent, led to highly regioselective benzylic C-O bond cleavage. This regioselectivity turnaround is discussed in terms of major solvent effects affecting the fragmentation paths of a common reaction intermediate. Synthetic applications of these findings led to the synthesis of biologically active compounds, like 2,5-dialkyl-substituted resorcinols, or 1-(3,4,5-trimethoxyphenyl)-2-arylethanes structurally related to combretastatin.
- Azzena, Ugo,Dettori, Giovanna,Mascia, Ilaria,Pisano, Luisa,Pittalis, Mario
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p. 11998 - 12006
(2008/03/14)
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- Practical synthesis of 2,3,4,5-tetramethoxytoluene
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The title compound, a key material for synthesis of coenzyme Q 10 , was effectively prepared in high yield by a reaction sequence starting from 3,4,5-trimethoxybenzadehyde via Wolff-Kishner reduction, Vilsmeier-Haack reaction, Dakin reaction, and methylation. Copyright Taylor & Francis Group, LLC.
- Ji, Yafei,Xu, Wanmei,Jin, Wenhu,Weimin, Yue
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p. 1961 - 1965
(2007/10/03)
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- Process development of the synthesis of 3,4,5-trimethoxytoluene
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3,4,5-Trimethoxytoluene (TMT) was synthesized, starting from p-cresol, through bromination followed by methylation to give 3,5-dibromo-4-methoxytoluene (DBMT). The methoxylation of the latter with sodium methoxide in methanol was studied under pressure and by continuous distillation of the solvent, methanol. The O-methylation reaction preceding the methoxylation was advantageous from the point of view of separation, purification, and isolation of the desired product and also in reducing the tar formation. The residue obtained was minimized to 0.6-0.7 wt % of the DBMT. The methoxylation reaction with distillative removal of methanol gave a conversion of 98% of DBMT to the mixture of methoxylated products, and the conversion to TMT was 86.5% as compared to 93% and 70.81%, respectively, when the reaction was carried out under pressure in a sealed reactor. However, the overall conversion to TMT based on p-cresol is 64.27% for the methoxylation reaction under pressure and 78.46% for the reaction by continuous removal of methanol calculated as isolated yield. The advantages of the methoxylation of the DBMT over the published literature procedures involving direct methoxylation of 3,5-dibromo-p-cresol followed by methylation of the dimethoxy-p-cresol are the ease of separation, purification, and isolation by vacuum fractionation of the desired product TMT.
- Sankaranarayanan, Ananthakrishnan,Chandalia
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p. 487 - 492
(2012/12/22)
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- Synthesis of 2,3-dimethoxy-5-methyl-1,4-benzoquinone: A key fragment in coenzyme-q series
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Preparation of the title compound by a reaction sequence starting from gallic acid present in mango kernel is described.
- Chida,Vani,Chandrasekharam,Srinivasan,Singh
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p. 657 - 660
(2007/10/03)
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- O-Methylation of 2,6-Dimethoxy-4-methylphenol by Aspergillus glaucus and Their Possible Contribution to Katsuobushi flavor
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Eleven strains of Aspergillus species, isolated from Katsuobushi (dried bonito) were grown in a liquid medium containing 2,6-dimethoxy-4-methylphenol, to examine the possibility of production of 1,2,3-trimethoxy-5-methylbenzene, which has a musty odor, during the molding process in Katsuobushi production.In the liquid medium 2,6-dimethoxy-4-methylphenol was O-methylated by 4 strains of A. glaucus. - Key words: Katsuobushi; Aspegillus species; O-methylation of phenols; musty odor; molding
- Yamauchi, Hajime,Doi, Mikiharu
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p. 1386 - 1387
(2007/10/03)
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- Production process of 1,4,5,8-naphthalene tetracarboxylic acid
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There is disclosed a mass production process of 1,4,5,8-naphthalene tetracarboxylic acid with high collection efficiency. In the presence of an alkaline metallic catalyst, 1,3-butadiene was added to the ethyl radicals of ethyl-p-xylene, and cyclized to 1,4,5,8-tetramethyl-1,2,3,4-tetrahydronaphthalene which was further dehydrogenated and oxidized to obtain 1,4,5,8-naphthalene tetracarboxylic acid, so that a constant supply of inexpensive 1,4,5,8-naphthalene tetracarboxylic acid can be achieved as an intermediate raw material for dye, pigment, resins, or the like.
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- Rearrangement of (Polymethoxybenzyl)ammonium N-Methylides
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Reaction of N,N-dimethyl-N-(polymethoxy-substituted benzyl)ammonium iodides 1a-e with cesium fluoride gave polymethoxy-substituted 5--6-methylene-1,3-cyclohexadienes 3 and 5 ( sigmatropic rearrangement products).However, these were quickly hydrolyzed to polymethoxytoluenes 8 during the aqueous workup.The pathway of the hydrolysis of 3 and 5 is discussed.
- Maeda, Yasuhiro,Shirai, Naohiro,Sato, Yoshiro,Tatewaki, Hiroshi
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p. 7897 - 7901
(2007/10/02)
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- The Photochemistry of Methoxy-Substituted Benzyl Acetates and Benzyl Pivalates: Homolytic vs Heterolytic Cleavage
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The multiple methoxy-substituted benzyl acetates (3g-i) and benzyl pivalates (4g-i) have been photolyzed in methanol solution.The products of these reactions are derived from two critical intermediates; the benzyl radical/acyloxy radical pair and the benzyl cation/carboxylate anion pair.As predicted by the meta effect, the yield of ion-derived product, the methyl ether in this case, was enhanced by the presence of the m-methoxy groups.The yield of ether, for the acetate esters, varied from 2percent for the 4-methoxy-substituted ester to 66percent for the 3,4,5-trimethoxy-substituted ester.In contrast, the yield of ether, for the pivalate esters, varied from 1percent for the 4-methoxy-substituted ester to 20percent for the 3,4,5-trimethoxy-substituted one.The meta effect does not explain these differences; electron transfer converting the radical pair to the ion pair is still an important pathway in the mechanism for ion formation.A quantitative analysis of the yield of the ethers was done in order to obtain the electron-transfer rate constants.This analysis revealed that the yield of the ethers was higher than expected based on previous results for other substituted benzyl acetates.A possible explanation for this discrepancy is that internal return of the radical pair to starting material for the acetate esters is more efficient than for the pivalate esters.Also, the esters 3k and 3l, were prepared to study the effect of electron-withdrawing groups in the meta position.For these esters, the benzylic cleavage reactions were inefficient and an isomerization reaction, the benzvalene rearrangement, was competitive.
- Pincock, J. A.,Wedge, P. J.
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p. 5587 - 5595
(2007/10/02)
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- Synthesis of crown ethers related to ubiquinones
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Crown ethers in which the two methoxy groups of ubiquinone-0 (2,3-dimethoxy-5-methyl-1,4-benzoquinone) are replaced by oligoethylene glycol bridges have been obtained in five straightforward steps in 35-40% overall yield from 5-methylpyrogallol. A Fremy salt oxidation of a phenolic precursor is used in the final step. The further elaboration of crown ether analogues of ubiquinone-2 was achieved by enol geranylation of cyclopentadiene adducts of the former quinones and subsequent retro-Diels-Alder reaction. The Claisen rearrangement of 2,2-dimethoxy-5-methylphenyl allyl ethers and related crown ethers affords ortho- and para-allyl-substituted phenols (3:1) that are oxidized to give bisnorubiquinone derivatives and their ortho-quinone isomers. All new compounds are characterized by high resolution NMR and mass spectrometry.
- Merz,Rauschel
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p. 797 - 802
(2007/10/02)
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- Oxidative Coupling of Lignans. III. Non-Phenolic Oxidative Coupling of Deoxypodorhizon and Related Compounds
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Oxidative coupling of deoxypodorhizon (4) with thallium(III) oxide and trifluoroacetic acid may be controlled to give either deoxyisopodophyllotoxin (14) or isostegane (16).These results and those with related non-phenolic substances indicate that the aromatic substituents of the parent diarylbutane play an important role in determining the outcome of oxidative coupling.
- Cambie, Richard C.,Craw, Peter A.,Rutledge, Peter S.,Woodgate, Paul D.
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p. 897 - 918
(2007/10/02)
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- Substituent and Ring Size Dependence of the 4J(Me-C-C-H) Coupling Constant
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The magnitude of the 4J proton-proton coupling constant across the fragment CH3-C-C-H (a probe of the bond order between the central sp2-sp2 hybridized carbon atoms) has been found to be essentially independent of substitution on a toluene fragment and the size of the ring containing the ortho-allylic fragment.The coupling constant is sensitive to direct substitution on the ortho-allilyc fragment, especially where the substituent is placed α to methyl group.KEY WORDS - 4J proton-proton coupling constant ortho-benzylic coupling constant ring size dependence substituent dependence
- Collins, M. J.,Hatton, P. M.,Sternbell, S.,Tansey, C. W.
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p. 824 - 828
(2007/10/02)
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- Ubiquinones and Related Compounds, XXXV. On Peracid Oxidation of 1-(Methoxy)-2,3-dimethoxy-5-methylbenzene
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The mechanism of the peracid oxidation of 1,2,3-trimethoxy-5-methylbenzene leading to 2,3-dimethoxy-5-methyl-1,4-benzoquinones has been investigated using 18O.The oxygen at the 1-position in the benzoquinone obtained originates from the oxidizing agent.
- Morimoto, Hiroshi,Hayashi, Nobuyoshi,Kawakami, Takeo
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p. 1963 - 1966
(2007/10/02)
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