- Synthesis of heteroaromatic trifluoromethyl ethers with trifluoromethyl triflate as the source of the trifluoromethoxy group
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A series of nitrogen-heterocycles have been transformed to the corresponding trifluoromethyl or higher perfluoroalkyl ethers by reaction of the corresponding N-oxides with trifluoromethyl or higher perfluoroalkyl triflate. Trifluoromethyl triflate, which has generally been used as a precursor to [OCF3]?, is used here as a bifunctional reagent to render the heteroarene more electrophilic and to deliver the trifluoromethoxy group. This reagent was easily prepared on a large scale (>100 grams) and is stable in either pure form or as a stock solution. Applications and limitations of this method are reported.
- Zhang, Qing-Wei,Hartwig, John F.
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- Phenanthridine-based nitrones as substrates for strain-promoted alkyne-nitrone cycloadditions
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Over the past decade, bioorthogonal chemistry that facilitates the efficient conjugation of biomolecules has expanded from the copper-catalyzed alkyne-azide cycloadditions to a multitude of diverse reactions, varying additives and reactional partners, and most often offering better alternatives with faster rates and lower toxicity of employed reactants. Among these, the copper-free strain-promoted cycloaddition reactions have been demonstrated to be more promising, offering a reaction without toxic metal catalysts and with faster inherent kinetic rate constants. The strain-promoted alkyne-nitrone cycloadditions are easily tunable from both the (strained) alkyne and nitrone perspective, both compounds giving the opportunity to modulate the rate of reaction by substituting various positions. Previously, acyclic nitrones have been evaluated in the strain-promoted alkyne-nitrone reactions; however, they were notably prone to hydrolysis. Some five-membered ring endocyclic nitrones developed concomitantly offered the advantage of relatively fast kinetics and better resistance to degradation in aqueous conditions and have been successfully used for labelling of biomolecules in living systems. Herein, we have prepared and studied nitrones inspired by the phenanthridine scaffold that efficiently undergo strain-promoted alkyne-nitrone reactions. Phenanthridine nitrones react fast with strained cyclooctynes with large bimolecular rate constants while maintaining bioorthogonality and resistance to hydrolysis.
- Strmiskova, Miroslava,Bilodeau, Didier A.,Chigrinova, Mariya,Pezacki, John Paul
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- 2-Position-selective C[sbnd]H fluoromethylation of six-membered heteroaryl N-oxides with (fluoromethyl)triphenylphosphonium iodide
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A mild and efficient method for the regioselective C[sbnd]H fluoromethylation of heteroaryl N-oxides with (fluoromethyl)triphenylphosphonium iodide is presented. With LiOt-Bu as the base and DMSO as the solvent, this reaction delivers a series of C2-fluor
- Hu, Chen-Chen,Hu, Wei-Qiang,Qing, Feng-Ling,Xu, Xiu-Hua
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- Deoxygenative Amination of Azine-N-oxides with Acyl Azides via [3 + 2] Cycloaddition
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A transition-metal-free deoxygenative C-H amination reaction of azine-N-oxides with acyl azides is described. The initial formation of an isocyanate from the starting acyl azide via a Curtius rearrangement can trigger a [3 + 2] dipolar cycloaddition of polar N-oxide fragments to generate the aminated azine derivative. The applicability of this method is highlighted by the late-stage and sequential amination reactions of complex bioactive compounds, including quinidine and fasudil. Moreover, the direct transformation of aminated azines into various bioactive N-heterocycles illustrates the significance of this newly developed protocol.
- Ghosh, Prithwish,Han, Sang Hoon,Han, Sangil,Kim, Dongeun,Kim, In Su,Kim, Saegun,Kwon, Na Yeon,Mishra, Neeraj Kumar
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p. 2476 - 2485
(2020/03/13)
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- Co(III)-Catalyzed C-H Amidation of Nitrogen-Containing Heterocycles with Dioxazolones under Mild Conditions
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A cobalt(III)-catalyzed C-8 selective C-H amidation of quinoline N-oxide using dioxazolone as an amidating reagent under mild conditions is disclosed. The reaction proceeds efficiently with excellent functional group compatibility. The utility of the current method is demonstrated by gram scale synthesis of C-8 amide quinoline N-oxide and by converting this amidated product into functionalized quinolines. Furthermore, the developed catalytic method is also applicable for C-7 amidation of N-pyrimidylindolines and ortho-amidation of benzamides.
- Dhiman, Ankit Kumar,Thakur, Ankita,Kumar, Inder,Kumar, Rakesh,Sharma, Upendra
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p. 9244 - 9254
(2020/08/14)
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- Visible-Light-Mediated C-H Alkylation of Pyridine Derivatives
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We report herein a visible-light-mediated C-H alkylation of pyridine derivatives that proceeds by simple combination of a large variety of N-alkoxypyridinium ions with alkanes in the presence of 2 mol % of fac-Ir(ppy)3 under blue illumination. The mild reaction conditions together with the high group functional tolerance make of this process a useful synthetic platform for the construction of structurally strained heterocycles. Detailed mechanistic investigations, including density functional theory calculations and quantum yield measurement, allowed us to understand factors controlling the reactivity and the selectivity of the reaction.
- Rammal, Fatima,Gao, Di,Boujnah, Sondes,Gaumont, Annie-Claude,Hussein, Aqeel A.,Lakhdar, Sami
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supporting information
p. 7671 - 7675
(2020/10/09)
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- Rh/O2-Catalyzed C8 Olefination of Quinoline N-Oxides with Activated and Unactivated Olefins
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The rhodium/O2 system-catalyzed distal C(sp2)-H olefination of quinoline N-oxides is developed. Molecular oxygen has been explored as an economic and clean oxidant, an alternative to inorganic oxidants. A wide substrate scope with respect to quinoline N-oxides and olefins (activated acrylates and styrenes; unactivated aliphatic olefins) demonstrates the robustness of the developed catalytic method. Interestingly, 2-substituted quinoline N-oxides also afforded good yields of the corresponding C8-olefinated products. Kinetic isotope studies and deuterium-labeling experiments have been performed to understand the preliminary mechanistic pathway. The applicability of the developed method is demonstrated by utilizing natural product-derived substrates and by converting the C8-olefinated quinoline N-oxides into various other useful molecules.
- Sharma, Ritika,Kumar, Rakesh,Sharma, Upendra
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p. 2786 - 2797
(2019/02/26)
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- 2-Position-Selective Trifluoromethylthiolation of Six-Membered Heteroaromatic Compounds
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The regioselective C-H trifluoromethylthiolation of six-membered heteroaromatic compounds via nucleophilic attack of a CF3S source on the electrophilically activated six-membered heteroaromatic ring was developed. The reaction proceeds in good yield with good functional group tolerance, even on a gram-scale. The key to the successful regioselective transformation is the presence of an additive (2,4-dinitrobenzenesulfonyl chloride). The regioselective trifluoromethylthiolation of quinidine derivative is also demonstrated. Trifluoromethylthiolation, followed by S-oxidation, affords the corresponding sulfones.
- Muta, Ryuhei,Torigoe, Takeru,Kuninobu, Yoichiro
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supporting information
(2019/06/13)
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- Electrochemical Deoxygenation of N-Heteroaromatic N -Oxides
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An electrochemical method for the deoxygenation of N-heteroaromatic N -oxide to give the corresponding N-heteroaromatics has been developed. Several classes of N-heterocycles such as pyridine, quinoline, isoquinoline, and phenanthridine are tolerated. The electrochemical reactions proceed efficiently in aqueous solution without the need for transition-metal catalysts and waste-generating reducing reagents.
- Xu, H.-C.,Xu, P.
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supporting information
p. 1219 - 1221
(2019/06/08)
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- An organocatalytic enantioselective direct α-heteroarylation of aldehydes with isoquinoline: N -oxides
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A new protocol for the enantioselective direct α-heteroarylation of aldehydes with isoquinoline N-oxides, via chiral enamine catalysis, has been successfully developed. High enantiomeric excesses and moderate to good yields were achieved for a variety of α-heteroarylated aldehydes.
- Bertuzzi, Giulio,Pecorari, Daniel,Bernardi, Luca,Fochi, Mariafrancesca
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supporting information
p. 3977 - 3980
(2018/04/23)
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- Visible-Light-Induced C2 Alkylation of Pyridine N-Oxides
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A photoredox catalytic method has been developed for the direct C2 alkylation of pyridine N-oxides. This reaction is compatible with a range of synthetically relevant functional groups for providing efficient synthesis of a variety of C2-alkylated pyridine N-oxides under mild conditions. Mechanistic studies are consistent with the generation of a radical intermediate along the reaction pathway.
- Zhang, Wen-Man,Dai, Jian-Jun,Xu, Jun,Xu, Hua-Jian
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p. 2059 - 2066
(2017/02/26)
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- Rhodium-Catalyzed Remote C-8 Alkylation of Quinolines with Activated and Unactivated Olefins: Mechanistic Study and Total Synthesis of EP4 Agonist
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Reported herein is a rhodium(III)-catalyzed regioselective distal C(sp2)-H bond alkylation of quinoline N-oxides using olefins as alkyl source and N-oxide as the traceless directing group. The reaction exhibits broad substrate scope with excellent selectivity for C-8 position and good yields of alkylated products. The usefulness of the developed catalytic protocol is established by synthesis of EP4 agonist. In mechanistic study, C-8 olefinated quinoline was identified as the reaction intermediate, which gets reduced to desired C-8 alkylated product in the presence of a rhodium(I) species (produced from rhodium(III) during reaction) and formic acid. Formic acid is produced from dimethylformamide in the presence of silver tetrafluoroborate. (Figure presented.).
- Sharma, Ritika,Kumar, Inder,Kumar, Rakesh,Sharma, Upendra
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supporting information
p. 3022 - 3028
(2017/09/08)
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- Catalyst and solvent-free alkylation of quinoline N-oxides with olefins: A direct access to quinoline-substituted α-hydroxy carboxylic derivatives
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A catalyst/solvent-free, one-pot and operationally simple method for the synthesis of quinoline-substituted α-hydroxy carboxylic derivatives by the hydroxyheteroarylation of olefins with quinoline N-oxides is reported. The reaction features a high atom-economy, mild and reagent/solvent-free conditions, broad substrate scope and good selectivity with high yields. A preliminary mechanistic study to shed light into the reaction pathway was also carried out.
- Kumar, Rakesh,Kumar, Inder,Sharma, Ritika,Sharma, Upendra
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supporting information
p. 2613 - 2617
(2016/03/05)
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- Regioselective Metal-Free Cross-Coupling of Quinoline N -Oxides with Boronic Acids
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A novel and operationally simple one-step C-H bond functionalization of quinoline N-oxides to 2-substituted quinolines was developed. This approach enables the regioselective functionalization under external oxidant- and metal-free conditions. The developed transformation represents the first application of the Petasis reaction in functionalization of heterocycles.
- Bering, Luis,Antonchick, Andrey P.
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supporting information
p. 3134 - 3137
(2015/06/30)
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- Insights into the mechanistic and synthetic aspects of the Mo/P-catalyzed oxidation of N-heterocycles
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A Mo/P catalytic system for an efficient gram-scale oxidation of a variety of nitrogen heterocycles to N-oxides with hydrogen peroxide as terminal oxidant has been investigated. Combined spectroscopic and crystallographic studies point to the tetranuclear Mo4P peroxo complex as one of the active catalytic species present in the solution. Based on this finding an optimized catalytic system has been developed. The utility and chemoselectivity of the catalytic system has been demonstrated by the synthesis of over 20 heterocyclic N-oxides.
- Larionov, Oleg V.,Stephens, David,Mfuh, Adelphe M.,Arman, Hadi D.,Naumova, Anastasia S.,Chavez, Gabriel,Skenderi, Behije
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p. 3026 - 3036
(2014/05/06)
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- Synthetic and mechanistic aspects of the regioselective base-mediated reaction of perfluoroalkyl- and perfluoroarylsilanes with heterocyclic N-oxides
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The scope and mechanistic implications of the direct transformation of heterocyclic N-oxides to 2-trifluoromethyl-, and related perfluoroalkyl- and perfluoroaryl-substituted N-heterocycles has been studied. The reaction is effected by perfluoroalkyl- and perfluorophenyltrimethylsilane in the presence of strong base. In situ displacement of the para-fluoro substituent in the pentafluorophenyl ring and the methoxy group in 8-methoxyquinolines with additional nucleophiles allows for further site-selective refunctionalization of the N-heterocyclic products. This journal is the Partner Organisations 2014.
- Stephens, David E.,Chavez, Gabriel,Valdes, Martin,Dovalina, Monica,Arman, Hadi D.,Larionov, Oleg V.
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supporting information
p. 6190 - 6199
(2014/08/05)
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- Synthesis and in Vitro Aldolase Reductase Inhibitory Activity of Compounds Containing an N-Acylglycine Moiety
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A number of N-benzoylglycines (6), N-acetyl-N-phenylglycines (7), N-benzoyl-N-phenylglycines (8), and tricyclic N-acetic acids (9-12) were synthesized as analogues of the N-acylglycine-containing aldolase reductase inhibitors alrestatin and 2-oxoquinoline-1-acetic acid.Derivatives of 6, which represent ring-simplified analogues of alrestatin, are very weak inhibitors of aldolase reductase obtained from rat lens, producing 50percent inhibition only at concentrations exceeding 100 μM.Compounds of series 7 were designed as ring-opened analogues of the 2-oxoquinolines.While this derivatives are more potent than compounds of series 6 (IC 50s of 6-80 μM), they are less active than the corresponding 2-oxoquinolines.Analogues of series 8 were designed as hybrid structures of both alrestatin and the 2-oxoquinoline-1-acetic acids.These compounds are substantially more potent than compounds of series 6 and 7 and display inhibitory activities comparable to or greater than alrestatin or the 2-oxoquinolines (IC 50s of 0.1-10 μM).Of the rigid analogues of 8, the most potent derivative is benzoxindol (12) with an IC 50 of 0.67 μM, suggesting that fusion of the two aromatic rings of 8 in a coplanar conformation may optimize affinity for aldose reductase in this series.
- DeRuiter, Jack,Swearingen, Blake E.,Wandrekar, Vinay,Mayfield, Charles A.
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p. 1033 - 1038
(2007/10/02)
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