- Halogen bonding matters: Visible light-induced photoredox catalyst-free aryl radical formation and its applications
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Photo-involving aryl halide activation plays a pivotal role in organic synthesis and materials science. Revealing the mechanism and understanding the photophysical and photochemical processes in the activation is of great importance. Here, we found that a
- Fang, Yu.,Liu, Fengyi,Ma, Jiani,Miao, Rong,Wang, Dan,Xiao, Jianliang,Xue, Dong
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- Visible-light induced disproportionation of pyrrole derivatives for photocatalyst-free aryl halides reduction
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As a green synthetic approach, visible light-driven photosynthesis is highly desirable in arylation of inert alkyl halides, as they are important precursors in the total synthesis of natural products and pharmaceuticals. However, the high bond dissociation energy of aryl halides is typically out of the range of a single visible-light photon. Here, we propose an essential initiation and subsequent electron-transfer step process for visible light-driven aryl halide reduction, and identify the key pyrrole radical anion intermediate, that acts as the strong reduction species. We propose a photoinduced disproportionation (PDP) approach without the addition of any photocatalysts or additives to afford radical anions of pyrrole derivatives, which have enough reduction power to transfer an electron to aryl halide, giving rise to the corresponding aryl radical to afford the desired C-H arylated heterocyclic product. Once generated, the heterocyclic product can undergo the same photoinduced disproportionation (PDP) process to activate aryl halides, thereby promoting the reaction rate. This unprecedented initiation step, which was carried out in the absence of photocatalysts and additives under ambient conditions, can also be used for coupling a wide range of (hetero)aryl halides and pyrrole derivatives, as well as the synthesis of drug intermediates and biorelevant compounds.
- Li, Zhi-Jun,Li, Shuya,Hofman, Elan,Hunter Davis, Andrew,Leem, Gyu,Zheng, Weiwei
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- Design, synthesis, and antiviral activity of a series of CD4-mimetic small-molecule HIV-1 entry inhibitors
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We presented our continuing stride to optimize the second-generation NBD entry antagonist targeted to the Phe43 cavity of HIV-1 gp120. We have synthesized thirty-eight new and novel analogs of NBD-14136, earlier designed based on a CH2OH “positional switch” hypothesis, and derived a comprehensive SAR. The antiviral data confirmed that the linear alcohol towards the “N” (C4) of the thiazole ring yielded more active inhibitors than those towards the “S” (C5) of the thiazole ring. The best inhibitor, NBD-14273 (compound 13), showed both improved antiviral activity and selectivity index (SI) against HIV-1HXB2 compared to NBD-14136. We also tested NBD-14273 against a large panel of 50 HIV-1 Env-pseudotyped viruses representing clinical isolates of diverse subtypes. The overall mean data indicate that antiviral potency against these isolates improved by ~3-fold, and SI also improved ~3-fold compared to NBD-14136. This new and novel inhibitor is expected to pave the way for further optimization to a more potent and clinically relevant inhibitor against HIV-1.
- Curreli, Francesca,Ahmed, Shahad,Benedict Victor, Sofia M.,Iusupov, Ildar R.,Spiridonov, Evgeny A.,Belov, Dmitry S.,Altieri, Andrea,Kurkin, Alexander V.,Debnath, Asim K.
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- Dichromatic Photocatalytic Substitutions of Aryl Halides with a Small Organic Dye
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Photocatalytic bond activations are generally limited by the photon energy and the efficiency of energy and electron transfer processes. Direct two-photon processes provide sufficient energy but the ultra-short lifetimes of the excited states prohibit chemical reactions. The commercial dye 9,10-dicyanoanthracene enabled photocatalytic aromatic substitutions of non-activated aryl halides. This reaction operates under VIS-irradiation via sequential photonic, electronic, and photonic activation of the simple organic dye. The resultant highly reducing excited photocatalyst anion readily effected C?H, C?C, C?P, C?S, and C?B bond formations. Detailed synthetic, spectroscopic, and theoretical studies support a biphotonic catalytic mechanism.
- Neumeier, Michael,Sampedro, Diego,Májek, Michal,de la Pe?a O'Shea, Víctor A.,Jacobi von Wangelin, Axel,Pérez-Ruiz, Raúl
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supporting information
p. 105 - 108
(2017/12/04)
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- Visible light catalysis method for dehalogenation of aryl halide without need of photooxidation reduction catalyst
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The invention discloses a visible light catalysis method for dehalogenation of aryl halide without the need of a photooxidation reduction catalyst, and belongs to the technical field of visible lightcatalysis organic synthesis. The method comprises the following steps that firstly, the aryl halide is weighed and placed in a reaction vessel, and a solvent is added; secondly, the reaction vessel isfilled with nitrogen for oxygen removal for 0-50 minutes, and alkali is added during the oxygen removal period; thirdly, the reaction vessel is sealed and placed over a light emitting diode with thewavelength of 400-500 nm and the power of 0.5-30 W for irradiation, and reacting is conducted for 3-48 hours at room temperature under the condition of stirring and then finished. By means of the method, the photooxidation reduction catalyst which is high in price or complex in synthesis is not needed, reacting can be achieved under the condition of the room temperature or under a mild condition,a reaction substrate is high in adaptability, and the reaction yield is high.
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Paragraph 0057; 0065; 0062
(2018/06/16)
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- Isomer-Specific Hydrogen Bonding as a Design Principle for Bidirectionally Quantitative and Redshifted Hemithioindigo Photoswitches
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A new class of bidirectionally quantitative photoswitches based on the hemithioindigo (HTI) scaffold is reported. Incorporation of a pyrrole hydrogen-bond donor leads to a bathochromic shift allowing for quantitative bidirectional isomerization. Additionally, extending conjugation from the electron-rich pyrrole results in quantitative visible-light photoswitches, as well as photoswitches that isomerize with red and near-infrared light. The presence of the hydrogen bond leading to the observed redshift is supported by computational and spectroscopic evidence.
- Zweig, Joshua E.,Newhouse, Timothy R.
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p. 10956 - 10959
(2017/08/21)
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- Chemoselective Radical Dehalogenation and C-C Bond Formation on Aryl Halide Substrates Using Organic Photoredox Catalysts
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Despite the number of methods available for dehalogenation and carbon-carbon bond formation using aryl halides, strategies that provide chemoselectivity for systems bearing multiple carbon-halogen bonds are still needed. Herein, we report the ability to tune the reduction potential of metal-free phenothiazine-based photoredox catalysts and demonstrate the application of these catalysts for chemoselective carbon-halogen bond activation to achieve C-C cross-coupling reactions as well as reductive dehalogenations. This procedure works both for conjugated polyhalides as well as unconjugated substrates. We further illustrate the usefulness of this protocol by intramolecular cyclization of a pyrrole substrate, an advanced building block for a family of natural products known to exhibit biological activity.
- Poelma, Saemi O.,Burnett, G. Leslie,Discekici, Emre H.,Mattson, Kaila M.,Treat, Nicolas J.,Luo, Yingdong,Hudson, Zachary M.,Shankel, Shelby L.,Clark, Paul G.,Kramer, John W.,Hawker, Craig J.,Read De Alaniz, Javier
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p. 7155 - 7160
(2016/08/30)
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- Copper-catalyzed 5-endo-trig cyclization of ketoxime carboxylates: A facile synthesis of 2-arylpyrroles
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A novel and facile copper-catalyzed 5-endo-trig cyclization of ketoxime carboxylates for the synthesis of 2-arylpyrroles has been developed. The reaction tolerates a range of functional groups and is a practical procedure for rapid synthesis of 2-arylpyrroles in high yields under mild conditions. the Partner Organisations 2014.
- Du, Wei,Zhao, Mi-Na,Ren, Zhi-Hui,Wang, Yao-Yu,Guan, Zheng-Hui
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p. 7437 - 7439
(2014/07/07)
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- Palladium-catalysed direct arylations of NH-free pyrrole and N-tosylpyrrole with aryl bromides
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The palladium-catalysed direct coupling of aryl halides with pyrroles provides a greener access to arylated pyrroles than more classical couplings such as Suzuki, Stille or Negishi reactions. However, so far, NH-free pyrrole and N-tosylpyrrole gave disappointing results for such couplings either in terms of regioselectivity of the arylation, catalyst loading or substrate scope. The reactivity of both NH-free pyrrole and N-tosylpyrrole was studied, and the tosylated pyrrole led to higher yields of coupling products due to better conversions of the aryl bromides. A range of aryl bromides undergo regioselective coupling at C2 of N-tosylpyrrole in moderate to good yields using 1 mol % [Pd(Cl(C3H5)]2 as the catalyst, KOAc as the base in DMAc.
- Bheeter, Charles Beromeo,Bera, Jitendra K.,Doucet, Henri
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experimental part
p. 509 - 513
(2012/02/02)
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- Optimization of the Suzuki coupling reaction in the synthesis of 2-[(2-substituted)phenyl]pyrrole derivatives
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A facile three-step synthesis of 2-(2-aminophenyl)pyrrole (1) and 2-[(2-aminomethyl)phenyl]pyrrole (2) is reported by use of Suzuki coupling of N-Boc-pyrrol-2-yl boronic acid (3) and o-substituted aryl halogenides, followed by hydrogenation. The Pd-catalyzed cross-coupling reaction is optimized to be applicable to a wide range of substitued aryl halogenides, with electron-donating and electron-withdrawing substituents, 5a-g. Moreover, Pd-catalyzed coupling of o-bromoaniline and 3 could be applied for the one-step preparation of pyrrolo[1,2-c]quinazolin-5(6H)-one (8). Copyright
- Aleskovic, Marija,Basaric, Nikola,Mlinaric-Majerski, Kata
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p. 1329 - 1335
(2012/01/04)
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- Direct arylation of pyrrole derivatives in ionic liquids
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An efficient methodology for the direct arylation of pyrrole derivatives has been developed. The reaction proceeds smoothly with a wide range of structurally diverse aryliodides. Derivatives bearing an N,N-dimethylamino group at the 1-position and an aryl substituent at the 2-position were prepared for the first time. This protocol is more environmentally friendly than those previously reported because it is free of transition metals and utilizes ionic liquids rather than volatile organic solvents.
- Vakuliuk, Olena,Gryko, Daniel T.
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experimental part
p. 2854 - 2859
(2011/06/26)
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- Triethanolamine-mediated palladium-catalyzed regioselective C-2 direct arylation of free NH-pyrroles
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An atom-economical phosphane-free palladium-catalyzed direct C-2 arylation of unactivated free NH-pyrroles is devised. This method provides a straithforward route to a wide variety of substituted 2-aryl-1H-pyrroles from readily accessible starting materials. Iodoarenes bearing electron-withdrawing and electron-donating substituents are tolerated under the presented reaction conditions. The scope of the reaction is also expanded to N-aryl and -alkylpyrroles albeit in lower yields.
- Jafarpour, Farnaz,Rahiminejadan, Soraya,Hazrati, Hamideh
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supporting information; experimental part
p. 3109 - 3112
(2010/07/15)
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- Delocalized Nitrogen Carbanions in SRN1 Reactions
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SRN1 reactions can be performed with nitrogen carbanions as nucleophiles, and generally the reaction leads to a mixture of isomers.In the case of the pyrrolyl anion, position 2 is about four times more reactive than position 3.When the ortho positions of pyrrole are substituted by alkyl groups, the reactivity of position 2 increases while that of position 3 decreases.With tert-butyl groups as the substituents, no reaction at position 2 is observed.With the indolyl anion as the nucleophile, no substitution at position 2 or at the phenyl ring is observed, and only one product corresponding to monosubstitution at position 3 is obtained.Imidazolyl anions react preferentially at position 4 (5), and substitution of position 2 by a methyl group makes the coupling regioselective.
- Chahma, M.,Combellas, C.,Thiebault, A.
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p. 8015 - 8022
(2007/10/03)
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- Electrosynthesis of arylpyrroles and -indoles under S(RN)1 conditions
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Arylpyrroles and -indoles are electrosynthesized via a S(RN)1 type reaction. With pyrrolyl anion, the reaction leads mainly to α-substitution, but β-substitution and disubstitution are also observed. With indolyl anion, the main product corresponds to β-substitution. In both cases, the yield of the main product is higher than 50%.
- Chahma,Combellas,Thiebault
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p. 366 - 368
(2007/10/02)
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- NEW METHODS FOR THE SYNTHESIS OF 2-ARYLPYRROLES
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Two short and efficient synthetic approaches for -mostly unknown- 2-arylpyrroles are presented.The key intermediates 3 are conveniently obtained from commercially available acetophenones 5 (method I) or benzoic acid derivatives 10, 11 (method II).
- Kruse, Chris G.,Bouw, Jan P.,Hes, Roelof van,Kuilen, Aalt van de,Hartog, Jack A. J. den
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p. 3141 - 3151
(2007/10/02)
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