- Stereochemistry of solvation of benzylic lithium compounds: Structure and dynamic behavior
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Several sec-benzylic lithium compounds, both externally coordinated, [α-(trimethylsilyl)benzyl]-lithium·PMDTA (12) and p-tert-butyl-α-(dimethylethylsilyl)benzyllithium·TMEDA (13), and internally coordinated, [α-[[[cis-2,5-bis(methoxymethyl)-1-pyrrolidinyl]methyl]dimethylsilyl]-p- tert-butylbenzyl]lithium (14) and [α-[[[(S)-2-(methoxymethyl)-1-pyrrolidinyl]methyl]dimethylsilyl]benzyl] lithium (15), have been prepared. Ring 13C NMR shifts indicate that 12-15 have partially delocalized structures. Externally solvated allylic lithium compounds are found to be delocalized, and only some internally coordinated species are partially delocalized. Compound 15 exists as > 95% of one stereoisomer of the two invertomers at Cα. This is in accord with a published ee of > 98% in products of the reactions of 15 with aldehydes. All four compounds show evidence of one-bond 13C-6Li spin coupling, ca. 3 Hz, which indicates a small detectable C-Li covalence. Averaging of the 13C-6Li coupling of 12 with increasing temperature provides the dynamics of intermolecular C-Li bond exchange, with ΔH?ex = 9 ± 0.5 kcal mol-1. Carbon-13 NMR line shape changes due to geminal methyls, and ligand carbons gave similar rates of inversion at Cα in 13 (externally solvated) and 14 (internally solvated), ΔH?inv ≈ 4.9 ± 0.5 kcal mol-1. By contrast, barriers to rotation around the ring-Cα bonds vary widely, depending on the mode of lithium coordination, ΔH?rot ≈ 8 ± 0.5 to 19 ± 1.0 kcal mol-1. Some mechanisms for these processes are proposed.
- Fraenkel, Gideon,Duncan, Joseph H.,Martin, Kevin,Wang, Jinhai
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Read Online
- Partial oxidation of 4-tert-butyltoluene catalyzed by homogeneous cobalt and cerium acetate catalysts in the Br-/H2O 2/acetic acid system: Insights into selectivity and mechanism
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The partial oxidation of 4-fert-butyltoluene to 4-tert-butylbenzaldehyde by hydrogen peroxide in glacial acetic acid, catalyzed by bromide ions in combination with cobalt(II) acetate or cerium(III) acetate, has been studied in detail. Based on the observed differences in reaction rates and product distributions for the different catalysts, a reaction mechanism involving two independent pathways is proposed. After the initial formation of a benzylic radical species, either oxidation of this intermediate by the metal catalyst or reaction with bromine generated in situ occurs, depending on which catalyst is used. The first pathway leads to the exclusive formation of 4-tert- butylbenzaldehyde, whereas reaction of the radical intermediate with bromine leads to formation of the observed side products 4-tert-butylbenzyl bromide and its hydrolysis and solvolysis products 4-tertbutylbenzyl alcohol and 4-tert-butylbenzyl acetate, respectively. The cobalt(II) catalysts Co(OAc) 2 and Co(acac)2 are able to quickly oxidize the radical intermediate, thereby largely preventing the bromination reaction (i.e., side-product formation) from occurring, and yield the aldehyde product with 75-80% selectivity, In contrast, the cerium catalyst studied here exhibits an aldehyde selectivity of around 50% due to the competing bromination reaction. Addition of extra hydrogen peroxide leads to an increased product yield of 72% (cerium(III) acetate) or 58% (cobalt(II) acetate). Product inhibition and the presence of increasing amounts of water in the reaction mixture do not play a role in the observed low incremental yields.
- Van De Water, Leon G. A.,Kaza, Arati,Beattie, James K.,Masters, Anthony F.,Maschmeyer, Thomas
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Read Online
- Readily Reconfigurable Continuous-Stirred Tank Photochemical Reactor Platform
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A new modular photochemical continuous stirred-tank reactor (CSTR) design is described, based upon the development of light-source units that can be fitted to the previously described fReactor CSTR platform. In addition to use in homogeneous photochemical reactions (e.g., photoredox-catalyzed hydroamination), these units are especially well suited to handling multiphasic mixtures, exemplified here in solid-liquid (Wohl-Ziegler bromination) and gas-liquid (photocatalytic oxidative decarboxylation) reactions. The use of slurries as input feeds allows for the intensification of photochemical brominations, while the modular nature of the system facilitates the simple integration of downstream reaction steps, exemplified here in a continuous synthesis of an intermediate for the antihypertensive drug valsartan.
- Blacker, A. John,Francis, Daniel,Kapur, Nikil,Marsden, Stephen P.
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supporting information
(2022/01/12)
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- Thiourea-Catalyzed C?F Bond Activation: Amination of Benzylic Fluorides
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We describe the first thiourea-catalyzed C?F bond activation. The use of a thiourea catalyst and Ti(OiPr)4 as a fluoride scavenger allows the amination of benzylic fluorides to proceed in moderate to excellent yields. Preliminary results with S- and O-based nucleophiles are also presented. DFT calculations reveal the importance of hydrogen bonds between the catalyst and the fluorine atom of the substrate to lower the activation energy during the transition state.
- Houle, Camille,Savoie, Paul R.,Davies, Clotilde,Jardel, Damien,Champagne, Pier Alexandre,Bibal, Brigitte,Paquin, Jean-Fran?ois
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supporting information
p. 10620 - 10625
(2020/07/24)
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- Photochemical benzylic bromination in continuous flow using BrCCl3 and its application to telescoped p-methoxybenzyl protection
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BrCCl3 represents a rarely used benzylic brominating reagent with complementary reactivity to other reagents. Its reactivity has been revisited in continuous flow, revealing compatibility with electron-rich aromatic substrates. This has brought about the development of a p-methoxybenzyl bromide generator for PMB protection, which was successfully demonstrated on a pharmaceutically relevant intermediate on 11 g scale, giving 91% yield and a PMB-Br space-time-yield of 1.27 kg L?1 h?1
- Otake, Yuma,Williams, Jason D.,Rincón, Juan A.,De Frutos, Oscar,Mateos, Carlos,Kappe, C. Oliver
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supporting information
p. 1384 - 1388
(2019/02/14)
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- Nucleophilic Substitutions of Alcohols in High Levels of Catalytic Efficiency
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A practical method for the nucleophilic substitution (SN) of alcohols furnishing alkyl chlorides, bromides, and iodides under stereochemical inversion in high catalytic efficacy is introduced. The fusion of diethylcyclopropenone as a simple Lewis base organocatalyst and benzoyl chloride as a reagent allows notable turnover numbers up to 100. Moreover, the use of plain acetyl chloride as a stoichiometric promotor in an invertive SN-type transformation is demonstrated for the first time. The operationally straightforward protocol exhibits high levels of stereoselectivity and scalability and tolerates a variety of functional groups.
- Stach, Tanja,Dr?ger, Julia,Huy, Peter H.
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supporting information
p. 2980 - 2983
(2018/05/28)
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- Systematic Evaluation of Sulfoxides as Catalysts in Nucleophilic Substitutions of Alcohols
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Herein, a method for the nucleophilic substitution (SN) of benzyl alcohols yielding chloro alkanes is introduced that relies on aromatic sulfoxides as Lewis base catalysts (down to 1.5 mol-%) and benzoyl chloride (BzCl) as reagent. A systematic screening of various sulfoxides and other sulfinyl containing Lewis bases afforded (2-methoxyphenyl)methyl sulfoxide as optimal catalyst. In contrast to reported formamide catalysts, sulfoxides also enable the application of plain acetyl chloride (AcCl) as reagent. In addition, it was demonstrated that weakly electrophilic carboxylic acid chlorides like BzCl promote Pummerer rearrangement of sulfoxides already at room temperature. This side-reaction also provided the explanation, why sulfoxide catalyzed SN-reactions of alcohols do not allow the effective production of aliphatic and electron deficient chloro alkanes. Comparison experiments provided further insight into the reaction mechanism.
- Motsch, Sebastian,Schütz, Christian,Huy, Peter H.
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supporting information
p. 4541 - 4547
(2018/09/13)
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- Copper-Mediated Trifluoromethylation of Benzylic Csp3?H Bonds
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Trifluoromethyl-containing compounds play a significant role in medicinal chemistry, materials and fine chemistry. Although direct C?H trifluoromethylation has been achieved on Csp2?H bonds, direct conversion of Csp3?H bonds to Csp3?CF3 remains challenging. We report herein an efficient protocol for the selective trifluoromethylation of benzylic C?H bonds. This process is mediated by a combination CuIII?CF3 species and persulfate salts. A wide range of methylarenes can be selectively trifluoromethylated at the benzylic positions. A combination of experimental and theoretical mechanistic studies suggests that the reaction involves a radical intermediate and a CuIII?CF3 species as the CF3 transfer reagent.
- Paeth, Matthew,Carson, William,Luo, Jheng-Hua,Tierney, David,Cao, Zhi,Cheng, Mu-Jeng,Liu, Wei
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p. 11559 - 11563
(2018/07/31)
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- Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo
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Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.
- Rana, Sujoy,Biswas, Jyoti Prasad,Sen, Asmita,Clémancey, Martin,Blondin, Geneviève,Latour, Jean-Marc,Rajaraman, Gopalan,Maiti, Debabrata
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p. 7843 - 7858
(2018/10/31)
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- Preparation and properties of a novel solution of hydrogen bromide (HBr) in 1,4-dioxane: An alternative reagent to HBr gas without protic solvents
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A solution of hydrogen bromide (HBr) in 1,4-dioxane was prepared and investigated for its ability to brominate alcohols, and hydrobrominate alkenes. This study revealed that the brominating ability of this HBr/1,4-dioxane solution is equal or superior to that of hydrobromic acid or HBr in acetic acid. The solution of HBr in 1,4-dioxane is robust, exhibiting no decomposition of the solvent, and retaining 97% of its original concentration, when kept at ?25 °C for 30 days. This solution is a liquid alternative to HBr gas without protic solvents.
- Nishio, Yuya,Mifune, Ryota,Sato, Taisuke,Ishikawa, Shin-ich,Matsubara, Hiroshi
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p. 1190 - 1193
(2017/03/02)
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- Silver-Catalyzed Decarboxylative Bromination of Aliphatic Carboxylic Acids
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The silver-catalyzed Hunsdiecker bromination of aliphatic carboxylic acids is described. With Ag(Phen)2OTf as the catalyst and dibromoisocyanuric acid as the brominating agent, various aliphatic carboxylic acids underwent decarboxylative bromination to provide the corresponding alkyl bromides under mild conditions. This method not only is efficient and general but also enjoys wide functional group compatibility. An oxidative radical mechanism involving Ag(II) intermediates is proposed.
- Tan, Xinqiang,Song, Tao,Wang, Zhentao,Chen, He,Cui, Lei,Li, Chaozhong
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supporting information
p. 1634 - 1637
(2017/04/11)
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- METHOD OF CONVERTING ALCOHOL TO HALIDE
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The present invention relates to a method of converting an alcohol into a corresponding halide. This method comprises reacting the alcohol with an optionally substituted aromatic carboxylic acid halide in presence of an N-substituted formamide to replace a hydroxyl group of the alcohol by a halogen atom. The present invention also relates to a method of converting an alcohol into a corresponding substitution product. The second method comprises: (a) performing the method of the invention of converting an alcohol into the corresponding halide; and (b) reacting the corresponding halide with a nucleophile to convert the halide into the nucleophilic substitution product.
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Page/Page column 50; 150; 182; 183
(2017/01/02)
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- Visible-Light-Induced Cyclization of Electron-Enriched Phenyl Benzyl Sulfides: Synthesis of Tetrahydrofurans and Tetrahydropyrans
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A new approach to the preparation of tetrahydrofurans and tetrahydropyrans through a photoredox catalytic process is described. The introduction of a phenylsulfanyl auxiliary group permits the substrates to be readily oxidized to form cationic intermediates for sequential intramolecular cyclization. The method features mild reaction conditions and operational simplicity.
- Li, Wei,Yang, Chao,Gao, Guo-Lin,Xia, Wujiong
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supporting information
p. 1391 - 1396
(2016/06/01)
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- 4-tert-butylbenzyl bromide preparing method
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The invention belongs to the field of chemical synthesis and provides a 4-tert-butylbenzyl bromide preparing method. The method comprises the steps of providing raw materials p-methyl tertiary butyl, hydrobromic acid and chlorite; dissolving p-methyl tertiary butyl in an organic solvent for oxidation reaction with hydrobromic acid and chlorite under the light condition, wherein oxidation reaction is conducted for 4-6 h, and the equation is shown in the specification. According to the method, the green oxidant and hydrobromic acid are adopted to provide the bromine source, selectivity is high, the conversion rate of obtained 4-tert-butylbenzyl bromide is high, the purity and yield are high, environment pollution is avoided, and the environment protection idea is realized. Furthermore, operation is easy, reaction is easy to control, reaction time is short, the technology is reliable, and industrialization is facilitated.
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Paragraph 0044-0050
(2017/03/08)
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- Microreactor-mediated benzylic bromination in concentrated solar radiation
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Sunlight-induced bromination of benzylic compounds was conducted in a capillary microreactor, resulting in mono-brominated compounds with yields of up to 94%. These reactions can be considered to be eco-friendly since they were carried out without an artificial light source or additional temperature control. In addition, up to 257.9mmol could be produced daily using cost-effective molecular bromine, which leads to potential improvement of industrial processes.
- Kim, Young Joon,Jeong, Myung Jin,Kim, Ji Eun,In, Insik,Park, Chan Pil
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p. 1653 - 1656
(2015/11/10)
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- A scalable procedure for light-induced benzylic brominations in continuous flow
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A continuous-flow protocol for the bromination of benzylic compounds with N-bromosuccinimide (NBS) is presented. The radical reactions were activated with a readily available household compact fluorescent lamp (CFL) using a simple flow reactor design based on transparent fluorinated ethylene polymer (FEP) tubing. All of the reactions were carried out using acetonitrile as the solvent, thus avoiding hazardous chlorinated solvents such as CCl4. For each substrate, only 1.05 equiv of NBS was necessary to fully transform the benzylic starting material into the corresponding bromide. The general character of the procedure was demonstrated by brominating a diverse set of 19 substrates containing different functional groups. Good to excellent isolated yields were obtained in all cases. The novel flow protocol can be readily scaled to multigram quantities by operating the reactor for longer time periods (throughput 30 mmol h-1), which is not easily possible in batch photochemical reactors. The bromination protocol can also be performed with equal efficiency in a larger flow reactor utilizing a more powerful lamp. For the bromination of phenylacetone as a model, a productivity of 180 mmol h -1 for the desired bromide was achieved.
- Cantillo, David,De Frutos, Oscar,Rincon, Juan A.,Mateos, Carlos,Oliver Kappe
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supporting information
p. 223 - 229
(2014/01/17)
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- One-pot transformation of methylarenes into aromatic aldehydes under metal-free conditions
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On the basis of studies of the transformation of benzylic bromides into the corresponding aromatic aldehydes by treatment with N-methylmorpholine N-oxide, various methylarenes were treated either with DBDMH in the presence of AIBN in acetonitrile at reflux (Method A) or with NBS in CCl4 under irradiation with a tungsten lamp at 30 °C (Method B), followed by treatment with N-methylmorpholine N-oxide to provide aromatic aldehydes in good yields. These methods could be adopted in one-pot transformations of methylarenes into aromatic aldehydes under conditions free of less toxic reagents and transition metals. Copyright
- Tabata, Masayuki,Moriyama, Katsuhiko,Togo, Hideo
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p. 3402 - 3410
(2014/06/09)
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- Enabling nucleophilic substitution reactions of activated alkyl fluorides through hydrogen bonding
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It was discovered that the presence of water as a cosolvent enables the reaction of activated alkyl fluorides for bimolecular nucleophilic substitution reactions. DFT calculations show that activation proceeds through stabilization of the transition structure by a stronger F···H 2O interaction and diminishing C-F bond elongation, and not simple transition state electrostatic stabilization. Overall, the findings put forward a distinct strategy for C-F bond activation through H-bonding.
- Champagne, Pier Alexandre,Pomarole, Julien,Therien, Marie-Eve,Benhassine, Yasmine,Beaulieu, Samuel,Legault, Claude Y.,Paquin, Jean-Francois
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supporting information
p. 2210 - 2213
(2013/06/26)
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- Direct oxidative conversion of methylarenes into aromatic nitriles
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A variety of methylarenes were successfully converted into the corresponding aromatic nitriles in good to moderate yields by the treatment with NBS or DBDMH in the presence of a catalytic amount of AIBN or BPO, followed by the reaction with molecular iodine in aq NH3 in a one-pot procedure. The present reaction is a useful and practical transition-metal-free method for the preparation of aromatic nitriles from methylarenes.
- Tsuchiya, Daisuke,Kawagoe, Yuhsuke,Moriyama, Katsuhiko,Togo, Hideo
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supporting information
p. 4194 - 4197
(2013/09/12)
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- Process for Producing Aromatic Aldehyde Compound
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A process for producing an aromatic aldehyde compound has steps of converting alkyl-substituted or non-substituted benzene into a compound of formula I by halomethylation, and allowing the compound of formula I and alkyl aldehyde to react in presence of phase transfer catalyst at a reaction temperature under alkaline condition to obtain the aromatic aldehyde compound.
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Page/Page column 3
(2012/10/23)
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- Microwave-promoted, one-pot conversion of alkoxymethylated protected alcohols into their corresponding nitriles, bromides, and iodides using [bmim][InCl4] as a green catalyst
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The Lewis acid room temperature ionic liquid, [bmim][InCl4], was found to be an efficient and green catalyst for the highly chemoselective and one-pot conversion of MOM- or EOM-ethers into their corresponding nitriles, bromides, and iodides under microwave irradiation. The procedures are simple, rapid, and high yielding. The catalyst exhibited a remarkable reactivity and is reusable.
- Mirjafari, Arsalan,Mohammadpoor-Baltork, Iraj,Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Khosropour, Ahmad Reza
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supporting information; experimental part
p. 3274 - 3276
(2010/07/18)
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- Benzylic bromination of toluene derivatives with boron tribromide
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A facile method for the benzylic bromination of toluene derivatives was developed. Various substituted toluenes were brominated with boron tribromide as bromine source in carbon tetrachloride at room temperature, affording their corresponding benzyl bromides in good yields.
- Chen, Hongbiao,Shen, Litao,Lin, Yuanbin
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experimental part
p. 998 - 1003
(2010/05/18)
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- Environmentally benign electrophilic and radical bromination 'on water': H2O2-HBr system versus N-bromosuccinimide
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A H2O2-HBr system and N-bromosuccinimide in an aqueous medium were used as a 'green' approach to electrophilic and radical bromination. Several activated and less activated aromatic molecules, phenylsubstituted ketones and styrene were efficiently brominated 'on water' using both systems at ambient temperature and without an added metal or acid catalyst, whereas various non-activated toluenes were functionalized at the benzyl position in the presence of visible light as a radical activator. A comparison of reactivity and selectivity of both brominating systems reveals the H2O2-HBr system to be more reactive than NBS for benzyl bromination and for the bromination of ketones, while for electrophilic aromatic substitution of methoxy-substituted tetralone it was higher for NBS. Also, higher yields of brominated aromatics were observed when using H2O2-HBr 'on water'. Bromination of styrene reveals that not just the structure of the brominating reagent but the reaction conditions: amount of water, organic solvent, stirring rate and interface structure, play a key role in defining the outcome of bromination (dibromination vs bromohydroxylation). In addition, mild reaction conditions, a straightforward isolation procedure, inexpensive reagents and a lower environment impact make aqueous brominating methods a possible alternative to other reported brominating protocols.
- Podgor?ek, Ajda,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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experimental part
p. 4429 - 4439
(2009/10/09)
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- Visible-light-promoted Wohl-Ziegler functionalization of organic molecules with N-bromosuccinimide under solvent-free reaction conditions
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The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-free reaction conditions (SFRC) was studied. The reaction took place in spite of the very restricted molecular motion; toluenes could be regioselectively converted to benzyl bromides. Selective radical-chain reactions with NBS were carried out in liquid/liquid and in solid/solid systems; furthermore, reactions could be performed in the presence of air. The radical scavenger TEMPO (=2,2,6,6-tetramethylpiperidin-1- yloxy) completely suppressed the side-chain bromination of toluenes with NBS under SFRC. Electron-withdrawing groups decreased the reactivity of the toluenes, and the Hammett reaction constant ρ+ = -1.7 indicated involvement of polar radical intermediates with electrophilic character.
- Jereb, Marjan,Zupan, Marko,Stavber, Stojan
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experimental part
p. 555 - 566
(2009/09/06)
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- Poly(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide), N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide and novel poly(N,N′-dibromo-N-phenylbenzene-1,3-disulfonamide) as powerful reagents for benzylic bromination
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N,N,N′,N′-Tetrabromobenzene-1,3-disulfonamide [TBBDA], poly(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) [PBBS], and novel poly(N,N′-dibromo-N-phenylbenzene-1,3-disulfonamide) [PBPS] can be used for bromination of benzylic positions in solvent.
- Ghorbani-Vaghei, Ramin,Chegini, Mohammad,Veisi, Hojat,Karimi-Tabar, Mehdi
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scheme or table
p. 1861 - 1865
(2009/07/19)
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- Benzylic brominations with N-bromosuccinimide in (Trifluoromethyl)benzene
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A variety of benzylic brominations were performed by using N-bromosuccinimide in (trifluoromethyl)benzene with photochemical activation in the presence of 2,2′-azobisisobutyronitrile, 1,1′- azobis(cyclohexanecarbonitrile), or benzoyl peroxide as the radical initiator. This system provides clean, rapid, and high-yielding reactions with replacement of conventional solvents, such as tetrachloromethane, by less-toxic (trifluoromethyl)benzene. Georg Thieme Verlag Stuttgart.
- Suarez, Diana,Laval, Gilles,Tu, Shang-Min,Jiang, Dong,Robinson, Claire L.,Scott, Richard,Golding, Bernard T.
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experimental part
p. 1807 - 1810
(2010/02/28)
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- Contrasting chemoselectivities in the ultrasound and microwave assisted bromination reactions of substituted alkylaromatics with N-bromosuccinimide
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Ultrasound and microwave assisted bromination reactions of various alkylaryls with N-bromosuccinimide, either neat or in water, shows diverse chemoselectivity. Thus, ring substitution occurs in water with ultrasound, whereas with microwaves both side-chain α-bromination and ring substitution occur. With neat reactants, side-chain α-bromination predominates for microwave assisted reactions. In the presence of water the chemoselectivity with microwave-promoted bromination is similar to that observed using classical methods.
- Heropoulos, Georgios A.,Cravotto, Giancarlo,Screttas, Constantinos G.,Steele, Barry R.
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p. 3247 - 3250
(2008/02/02)
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- Visible light induced 'on water' benzylic bromination with N-bromosuccinimide
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Benzylic bromination of various 4-substituted toluenes (Me, tert-Bu, COOEt and COMe) was effectively conducted with NBS in pure water and with a 40 W incandescent light-bulb as an initiator of the radical chain process, while electron donating groups (OMe and NHAc) directed the reaction to electrophilic aromatic substitution.
- Podgor?ek, Ajda,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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p. 1097 - 1099
(2007/10/03)
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- Association of fluorous "phase-vanishing" method with visible-light activation in benzylic bromination by bromine
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In this study the "phase-vanishing" method for diffusion-controlled addition of a reagent (Br2) to a reaction phase via a fluorous membrane (C8F18) is combined with an additional mode of activation (visible-light) to achieve the benzyl bromination of various alkyl-substituted aromatic compounds in a concentrated solution. Benzyl bromination of p-tert-butyl-toluene proceeded in various solvents including hexane and methanol, while the reaction of the neat substrate showed a similar selectivity as in carbon tetrachloride. The effect of the substituent on the para position of toluene on the course of bromination revealed three processes: benzyl bromination with H, Me, tBu and CO2Et substituents, aromatic bromination with OMe and NHAc substituents and the reaction of the 4-acetyl derivative at the substituent to form an α-bromo ketone. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Podgorsek, Ajda,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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p. 483 - 488
(2007/10/03)
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- Free radical bromination by the H2O2-HBr system on water
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An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 40 W incandescent light bulb serves as a source of bromine radicals. Various substituted toluenes (H, Me, tBu, Br, COOEt, COPh, NO2) were brominated at the benzyl position. This haloperoxidase-like system for benzylic bromination does not require the presence of metal ions or an organic solvent for efficient conversion of methyl-arenes to benzyl bromides.
- Podgor?ek, Ajda,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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p. 7245 - 7247
(2007/10/03)
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- Blue light-emitting compound for organic electroluminescent device and organic electroluminescent device using the same
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The present invention relates to a blue light-emitting compound for organic polymer EL devices and organic EL devices having superior color purity and light-emitting efficiency by providing a blue light-emitting compound for organic EL devices represented by Chemical Formula 1 and an organic EL device using the blue light-emitting compound: 1wherein R1 to R8 each independently represents a functional group selected from the group consisting of alkyl groups, alkoxy groups, carbon rings, aryl groups, hetero rings and fused aromatic compounds having from 1 to 30 carbon atoms.
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- Oxidation of the Methyl Group at the Aromatic Nucleus with Molecular Oxygen in the Presence of N-Bromosuccinimide under Photoirradiation
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A methyl group at the aromatic nucleus can be oxidized to the corresponding carboxylic acid directly in the presence of N-bromosuccinimide (NBS) under photoirradiation. By considering both the promoting effect of oxygen and a catalytic amount of NBS, aerobic oxidation via hydroperoxide, which is thought to be generated by abstraction of a hydrogen with a bromo radical from NBS, proceeded.
- Itoh, Akichika,Kodama, Tomohiro,Hashimoto, Shouei,Masaki, Yukio
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p. 2289 - 2291
(2007/10/03)
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- Amine derivatives
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The present invention relates to amine derivatives represented by formula (1) or salts thereof. R3represents C1-C3 alkyl, hydroxylated C1-C5 alkyl, C1-C5 acyl; C2-C5 alkenyl, or a halogen atom; and k, l, and m are each an integer of 1 to 4.) Exhibiting excellent antifungal effect, these compounds are highly useful as antifungal agents, antifungal compositions, drugs, etc.
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- Environmentally-friendly Wohl-Ziegler bromination: Ionic-liquid reaction and solvent-free reaction
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Environmentally-friendly Wohl-Ziegler bromination of benzylic methyl groups was successfully camed out in ionic-liquid and solvent-free systems, to produce the corresponding benzylic bromides in good to moderate yields.
- Togo, Hideo,Hirai, Takeshi
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p. 702 - 704
(2007/10/03)
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- Novel, strained 10b,10c-dihydropyrenes bearing bulky TMSCH2 groups at the internal positions
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Two novel, strained trans-10b,10c-dihydropyrenes, 9a-b, with internal, bulky trimethylsilylmethyl substituent(s) were synthesized. Their 14π-electron annulene systems were found to be distorted, as shown by X-ray crystallographic analyses and 1H-NMR and UV spectroscopy.
- Sawada, Tsuyoshi,Wakabayashi, Masaki,Takeo, Hiromi,Miyazawa, Akira,Tashiro, Masashi,Thiemann, Thies,Mataka, Shuntaro
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p. 403 - 407
(2007/10/03)
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- Thermodynamic Stabilities of Phenonium Ions Based on Bromide-Transfer Equilibria in the Gas Phase
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The thermodynamic stabilities of the phenonium (ethylenebenzenium) ion and ring-substituted derivatives were determined based on the bromide-transfer equilibria in the gas phase. It has been shown that the phenonium ion is 2.4 kcal mol-1 more stable than the t-butyl cation, and that the substituent effect on its stability can be correlated with the Yukawa-Tsuno equation with a ρ value of -12.6 and an r+ of 0.62. An r+ value smaller than unity of the α-cumyl(1-methyl-1-phenylethyl) cation suggested that π-delocalization in the phenonium ion is essentially less effective than through a benzylic π-interaction. On the other hand, the ρ value of -12.6 is distinctly larger than that for the ordinary benzylic carbocation systems, but is comparable to that of the benzenium ion. In addition, it has been found that the r+ value of the phenonium ions in the gas phase is in complete agreement with that for the aryl-assisted process in the acetolysis of 2-arylethyl toluenesulfonates. This suggests that the degree of π-delocalization of the positive charge is the same in the transition state and the intermediate cation. It is concluded that an r+ value of 0.6, which is ranked at a unique position in the continuous spectrum of the resonance demand, is characteristic of the bridged structure of the phenonium ion intermediate and the transition state.
- Mustanir,Mishima, Masaaki,Fujio, Mizue,Tsuno, Yuho
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p. 1401 - 1407
(2007/10/03)
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- Scavenger assisted combinatorial process for preparing libraries of tertiary amine compounds
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This invention relates to a novel solution phase process for the preparation of tertiary amine combinatorial libraries. These libraries have utility for drug discovery and are used to form wellplate components of novel assay kits.
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- Design and synthesis of novel 2,7-dialkyl substituted 5(S)-amino-4(S)-hydroxy-8-phenyl-octanecarboxamides as in vitro potent peptidomimetic inhibitors of human renin
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Novel low-molecular weight transition-state peptidomimetic renin inhibitors characterized by an all-carbon 8-phenyl substituted octanecarboxamide skeleton have been discovered based on a topographical design approach. The in vitro most potent inhibitors 21, 25 and 26 incorporating a strong H-bond acceptor group linked to the benzyl spacer of the (P3-P1)-unit had IC50s in the low nanomolar range against human renin.
- Goeschke, Richard,Cohen, Nissim Claude,Wood, Jeanette M.,Maibaum, Juergen
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p. 2735 - 2740
(2007/10/03)
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- The Oxidation of Substituted Toluenes to Benzaldehydes using Solid Peroxygen Sources in the Presence of Bromide and Cobalt(II) Acetate
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The oxidation of substituted toluenes to benzaldehydes in the presence of bromide anion and cobalt(II) acetate has been studied using solid peroxygen sources in place of aqueous hydrogen peroxide as the primary active oxygen source.The solid peroxygen's screened were, sodium carbonate sesquiperhydrate (PCS, Na2CO3*1.5H2O2), sodium perborate monohydrate (PBS-1, NaBO3*H2O), sodium perborate tetrahydrate (PBS-4, NaBO3*4H2O) and urea hydrogen peroxide (UHP, NH2CONH2*H2O2).PBS-1 was found to be the most selective primary oxidant for aldehyde production.For example, when 4-t-butyl toluene was oxidized, the aldehyde was formed at a selectivity exceeding 90 percent, whereas, when aqueous hydrogen peroxide was employed the selectivity to the aldehyde dropped dramatically to below 50 percent.The increased selectivity to the aldehyde can be explained in terms of the primary oxidant's structure, the temperature at which the reaction was operated, and the mole ratios of cobalt(II) to bromide and primary oxidant to substrate.The addition of solid peroxygens effectively suppresses over-oxidation to the carboxylic acids.
- Jones, Craig W.,Hackett, Anthony,Pattinson, Ian,Johnstone, Alexander,Wilson, Sharon L.
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p. 2501 - 2525
(2007/10/03)
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- Chemoenzymatic process for production of S fenpropimorph
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A process for stereoselective (enantioselective) production of S-(-)-fenpropimorph, which process comprises reacting 4-tert-butylbenzylchloride or bromide with methyldiethylmalonate, decarbethoxylation of the product into racemic 3-(4-tert-butylphenyl)-2-methylpropionic acid ethyl ester in DMSO in the presence of alkali cations, then Pseudomonas sp.lipase catalyzed resolution of racemic ester to S-(-)-acid, base-catalyzed racemisation and recycling of the R-(+)-ester, acylation of cis-2,6-dimethylmorpholine with the activated derivative of S-(-)-acid, and final reduction of the intermediary amide to provide optically (enantiomerically) pure S-(-)-fenpropimorph. The key enzymatic reaction is fast, employs inexpensive commercially available enzyme, requires minimal work-up, and can therefore easily be performed on a large scale.
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- Electron Paramagnetic Resonance Spectra of Substituted 1- and 2-Naphthylmethyl Radicals
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The EPR spectra of 7-tert-butyl-1-naphthylmethyl and 6-tert-butyl-2-naphthylmethyl radicals, prepared by photolysis of the hydrocarbon with tert-butyl peroxide at -40 deg C, have been analysed by correlation methods: average α(C-H) coupling constants are 15.0 and 15.25 G respectively, in line with the expected relative stabilities of the two radicals and the recently reported stabilization energy for 1-naphthylmethyl.
- Jackson, Richard A.,Rhodes, Christopher J.
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- Evidence for the Formation of Nitrenium Ions in the Acid-catalysed Solvolysis of Mutagenic N-Acetoxy-N-Alkoxybenzamides
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In aqueous acetonitrile, N-acetoxy-N-alkoxybenzamides undergo acid-catalysed solvolysis by the AAl1 mechanism to give acetic acid and nitrenium ions.This is indicated by an inverse dependence of the acid-independent rate constant, kH, upon the activity of water, a solvent kinetic isotope effect of 0.44 and positive Σ(excit.) values.In addition, relief of steric compression at the nitrogen enhances the rate of solvolysis.Hammett correlations with ?+ substituent constants were found for the rates of solvolysis of para-substituted-N-acetoxy-N-butoxybenzamides and N-acetoxy-N-(para-substituted benzyloxy) benzamides.This fact and the low ρ-values of -1.35 and -1.56, respectively, are indicative of a strong build-up of positive charge in the transition state which has both nitrenium ion and oxonium ion character and is in accordance with computed molecular-orbital properties of N-alkoxynitrenium ions.Greater levels of mutagenicity have been measured for those compounds which are more readily solvolysed to nitrenium ions.
- Campbell, John J.,Glover, Stephen A.,Hammond, Gerard P.,Rowbottom, Colleen A.
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p. 2067 - 2080
(2007/10/02)
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- ORGANIC PHOSPHORUS COMPOUNDS 91. SYNTHESIS AND PROPERTIES OF 1-AMINO-2-ARYLETHYLPHOSPHONIC AND -PHOSPHINIC ACIDS AS WELL AS -PHOSPHINE OXIDES
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The preparation, physical and spectroscopic properties of 1-amino-2-arylethylphosphonic, and -phosphinic acids as well as -phosphine oxides, the phosphorus analogues of phenylalanine are described, and the reactions of 1-amino-2-(4-fluorophenyl)ethylphosphonates with acetals, isocyanides, esters, acid anhydrides, activated aromatic nitro- and halogen compounds, and with N-protected alanine are reported.It is shown that several of the 1-amino-2-arylethylphosphonic acids are strong inhibitors of PAL and anthocyanin synthesis and also are quite active botryticides.Among the active compounds were 1-amino-2-(4-fluorophenyl)ethylphosphonic acid, 3f, and the methyl-substituted compounds 3k, 3l, and 3m.The fluoroderivative 3f was also effective as a seed-dressing agent in barley showing a 100percent protection against the fungus Fusarium nivale at 600 ppm.
- Maier, Ludwig
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- Retinobenzoic acids. 3. Structure-activity relationships of retinoidal azobenzene-4-carboxylic acids and stilbene-4-carboxylic acids
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Alkyl-substituted azobenzene-4-carboxylic acids are potent differentiation inducers of human promyelocytic leukemia cell line HL-60 to mature granulocytes. Their structure-activity relationships are very similar to those of other retinoidal benzoic acids which are generally represented by 4 and named retinobenzoic acids. The structure-activity relationships of azobenzenecarboxylic acids can also be applied to the known retinoid TTNPB (3). Thus, (E)-4-[2-(3,4-diisopropylphenyl)-1-propenyl]benzoic acid (St30 (28)), and (E)-4-[2-(3-tert-butylphenyl)ethenyl]benzoic acid (St40) (29)), the acyclic alkyl analogues of TTNPB, are nearly as active as retinoic acid. Among the oxidatively derived compounds (Az90, Ep series and Ox series) of azobenzene- or stilbenecarboxylic acids, Az90 (71) and Ep80 (61) have strong activities. However, all the bishydroxylated derivatives of TTNPB are inactive, while a diketo analogue Ox580 (69) has only weak potency. The activities of conformationally restricted compounds of TTNPB offer some information on the stereochemistry of the active form of these retinoidal compounds.
- Kagechika,Himi,Namikawa,Kawachi,Hashimoto,Shudo
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p. 1098 - 1108
(2007/10/02)
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