- Mechanistic Studies of the Fischer Indole Reaction
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Kinetic and solvent isotope effects were measured for the Fischer indole reactions of four hydrazones.Under neat acid conditions (5percent P2O5/MeSO3H) the KIE's ranged from 3.2 to 5.8, while the solvent isotope effects (kH/kD) ranged from 0.4 to 0.7.Under dilute acid conditions in sulfolane solvent, both isotope effects were near unity.The large kinetic isotope effect and large inverse solvent isotope effect, along with the observation that isotopic exchange occurs in the aromatic ring of the hydrazones, suggest that a preequilibrium protonation of the aromatic ring occurs followed by the rate-determining ene-hydrazine formation under the neat acid conditions.In contrast, under the dilute acid conditions, the lack of isotope effects and the lack of ring isotope exchange indicate that no ring protonation is occurring, that ene-hydrazine formation is no longer rate-determining, and that the rate-limiting step is now most likely the rearrangement.
- Hughes, David L.,Zhao, Dalian
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- Asymmetric transfer hydrogenation of heterocycle-containing acetophenone derivatives using N-functionalised [(benzene)Ru(II)(TsDPEN)] complexes
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The application of enantiomerically-pure ruthenium(II) catalysts containing N - functionalised TsDPEN ligand to the asymmetric transfer hydrogenation of 15 examples of α-heterocyclic acetophenone derivatives is reported. Products of up to 99% ee were formed.
- Barrios-Rivera, Jonathan,Xu, Yingjian,Clarkson, Guy J.,Wills, Martin
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supporting information
(2021/12/02)
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- Inverting Conventional Chemoselectivity in the Sonogashira Coupling Reaction of Polyhalogenated Aryl Triflates with TMS-Arylalkynes
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A newly developed phosphine ligand with a C2-cyclohexyl group on the indole ring was successfully applied in a chemoselective Sonogashira coupling reaction with excellent chemoselectivity, affording an inversion of the conventional chemoselectivity order of C–Br > C–Cl > C–OTf. This study also provided an efficient approach to the synthesis of polycyclic aromatic hydrocarbons (PAHs) and the natural product analogue trimethyl-selaginellin L by merging of chemoselective Sonogashira and Suzuki–Miyaura coupling reactions.
- Wang, Miao,So, Chau Ming
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supporting information
p. 681 - 685
(2022/01/20)
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- Facile C-S Bond Cleavage of Aryl Sulfoxides Promoted by Bronsted Acid
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A method for the Bronsted acid promoted desulfination of aryl sulfoxides is presented. In the presence of a thiol, electron-rich sulfoxides undergo C-S bond cleavage to give the corresponding protodesulfinated arenes and disulfides.
- Brutiu, Bogdan R.,Klose, Immo,Maulide, Nuno
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p. 488 - 490
(2021/03/09)
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- Preparation method of nitrogen-alkyl (deuterated alkyl) aromatic heterocycle and alkyl (deuterated alkyl) aryl ether compound
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The invention provides a method for preparing nitrogen-alkyl(deuterated alkyl)aromatic heterocycle and alkyl(deuterated alkyl)aryl ether compounds. The method adopted in the invention specifically comprises the following steps: firstly, adding an alkoxy base (MOR') or a combination reagent Q (comprising a base M'X, an alcohol C and a molecular sieve E) into a solvent B to be stirred; then, addingan aromatic compound D of nitrogen sulfonyl or oxygen sulfonyl into a mixture; separating and purifying after reaction to obtain nitrogen-alkyl(deuterated alkyl)aromatic heterocycle or alkyl(deuterated alkyl)aryl ether. The method can realize one-step conversion from an electron withdrawing benzenesulfonyl protecting group on a nitrogen or oxygen atom to an electron donating alkyl protecting group, avoids using highly toxic alkyl halide, and has advantages of being efficient, economical, environmentally friendly, mild in condition, good in substrate universality and high in yield; the prepareddeuterated compounds can be widely applied to the fields of pharmaceutical chemistry and organic chemistry synthesis.
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Paragraph 0087-0092
(2021/04/03)
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- Synthesis of 3-halogenated 2,3′-biindoles by a copper-mediated 2,3-difunctionalization of indoles
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A copper-mediated 2,3-difunctionalization of indoles to afford 3-halogenated 2,3′-biindoles is described herein. The protocol uses readily available feedstocks and a naturally abundant copper catalyst system, which allows the regioselective formation of C-C and C-X (X = Cl & Br) bonds in one single operation. Here the copper metal salt serves not only as a catalyst but also as a reactant to provide the source of halogen. This operationally simple procedure avoids the utilization of environmentally unfriendly reagents and displays good functional group compatibility. Noteworthily, the introduction of halogen into molecules would offer great potential for further chemical transformations. This journal is
- Gu, Xiaoting,Liang, Taoyuan,Wei, Wanxing,Zhang, Xiaoxiang,Zhang, Yingying,Zhang, Zhuan
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supporting information
p. 10403 - 10407
(2021/12/17)
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- Compound used as blue pressure-sensitive dye and preparation method and application thereof
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The invention relates to a compound used as a blue pressure-sensitive dye, and the structural general formula of the compound is shown in the specification, in the formula, R1 is CH3, CH2CH3, CH2CH2CH3 or CH2CH2CH2CH3; and R2 is CH3 or CH2CH3. Three key intermediates including substituted indole, reactive hydrogen substituted m-aminophenol and chlorophthalic anhydride are adopted, and the target compound used as the blue pressure-sensitive dye is obtained through two-step condensation. Raw materials required for synthesis are easy to obtain, the conversion rate of each step in the synthesis process is high, and no complex purification procedure is needed in the intermediate process. The target compound is high in color rendering property, the molar absorption coefficient of the target compound reaches 1.8 times that of CVL, and the same color rendering effect of CVL can be achieved under the low pressure-sensitive dye using concentration.
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Paragraph 0020
(2021/02/06)
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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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- A rhodium(ii) catalysed domino synthesis of azepino fused diindoles from isatin tethered: N -sulfonyl-1,2,3-triazoles and indoles
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An efficient and convenient protocol for the synthesis of a novel class of azepino fused diindoles from isatin tethered N-sulfonyl-1,2,3-triazoles and indoles has been disclosed. The reaction proceeds via denitrogenative aza-vinyl rhodium carbene formation to give a carbonyl ylide, which with indole results in 1,3-dipolar cycloaddition followed by sequential semipinacol rearrangement/ring expansion/oxidation to produce azepino fused diindoles. The reaction shows a broad substrate scope giving up to 81% yield. Furthermore, reversible catalytic hydrogenation and photophysical studies were carried out to demonstrate the application of these molecules.
- Kahar, Nilesh,Jadhav, Pankaj,Reddy, R. V. Ramana,Dawande, Sudam
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supporting information
p. 1207 - 1210
(2020/02/04)
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- Ir-Catalyzed Reversible Acceptorless Dehydrogenation/Hydrogenation of N-Substituted and Unsubstituted Heterocycles Enabled by a Polymer-Cross-Linking Bisphosphine
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The polystyrene-cross-linking bisphosphine ligand PS-DPPBz was effective for the Ir-catalyzed reversible acceptorless dehydrogenation/hydrogenation of N-heterocycles. Notably, this protocol is applicable to the dehydrogenation of N-substituted indoline derivatives with various N-substituents with different electronic and steric natures. A reaction pathway involving oxidative addition of an N-adjacent C(sp3)-H bond to a bisphosphine-coordinated Ir(I) center is proposed for the dehydrogenation of N-substituted substrates.
- Zhang, Deliang,Iwai, Tomohiro,Sawamura, Masaya
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supporting information
p. 5240 - 5245
(2020/07/03)
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- Catalytic Aerobic Dehydrogenatin of N-Heterocycles by N-Hydoxyphthalimide
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Catalytic methods for the aerobic dehydrogenation of N-heterocycles are reported. In most cases, indoles are accessed efficiently from indolines using catalytic N-hydroxyphthalimide (NHPI) as the sole additive under air. Further studies revealed an improved catalytic system of NHPI and copper for the preparation of other heteroaromatics, for example quinolines. (Figure presented.).
- Chen, Weidong,Tang, Hao,Wang, Weilin,Fu, Qiang,Luo, Junfei
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supporting information
p. 3905 - 3911
(2020/08/10)
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- Method for preparing indole compound through air oxidation catalyzed by N-hydroxyphthalimide
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The invention discloses a method for preparing an indole compound through non-transition metal catalyzed air oxidation. According to the method, the low-cost N-hydroxyphthalimide is used as a catalystand air is used as an oxidizing agent, wherein indoline compounds are oxidized in an organic solvent, and synthesis of the indoline compounds is achieved. The method has the advantages of simple reaction operation, low reaction cost, high yield, mild conditions, no heavy metal pollution and the like.
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Paragraph 0086-0088
(2020/11/23)
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- Bisketene Equivalents as Diels-Alder Dienes
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2,5-Bis(tert-butyldimethylsilyloxy)furans are established as vicinal bisketene equivalents for application as dienes in the Diels-Alder reaction. Cycloaddition with olefinic dienophiles, under exceptionally mild conditions, enables convergent access to highly substituted para-hydroquinones in unprotected form via a one-pot Diels-Alder/ring-opening/tautomerization sequence. The synthesis of para-benzoquinones from acetylenic dienophiles, including benzynes, is also demonstrated, and 2,5-bis(tert-butyldimethylsilyloxy)pyrroles are established as competent dienes for the synthesis of para-iminoquinones. Application in natural product synthesis enables gram-scale access to the neuroprotective agent (±)-indanostatin.
- Dissanayake, Isuru,Hart, Jacob D.,Becroft, Emma C.,Sumby, Christopher J.,Newton, Christopher G.
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supporting information
p. 13328 - 13333
(2020/09/03)
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- Highly Efficient Synthesis of Hindered 3-Azoindoles via Metal-Free C-H Functionalization of Indoles
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Although 3-azoindoles have recently emerged as an appealing family of photoswitch molecules, the synthesis of such compounds has been poorly covered in the literature. Herein a high-yielding and operationally simple protocol is reported allowing the synthesis of 3-azoindoles, featuring important steric hindrance around the azo motif. Remarkably, this C-H coupling is characterized by excellent atom economy and occurs under metal-free conditions, at room temperature, and within few minutes, delivering the expected products in excellent yields (quantitatively in most of the cases). Accordingly, a library of new molecules, with potential applications as photochromic compounds, is prepared.
- Guillemard, Lucas,Jacob, Nicolas,Wencel-Delord, Joanna
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p. 574 - 580
(2020/02/13)
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- Sulfoxide-Promoted Chlorination of Indoles and Electron-Rich Arenes with Chlorine as Nucleophile
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An efficient chlorination of indoles and electron-rich arenes with chlorine anion as nucleophile is described. With the use of ethyl phenyl sulfoxide as the promoter, the reaction went smoothly under metal-free and mild conditions. Various indoles and electron-rich arenes are converted into the corresponding chlorinated compounds in moderate to excellent yields. A plausible interrupted Pummerer reaction mechanism was proposed without the oxidation of chloride anion. In addition, the byproduct thioether could be easily converted to the starting material sulfoxide just by a simple oxidation reaction. (Figure presented.).
- Ji, Yuan-Zhao,Li, Hui-Jing,Wang, Yi-Ruo,Wu, Yan-Chao,Zhang, Zheng-Yan
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supporting information
(2020/02/05)
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- Additions of Aldehyde-Derived Radicals and Nucleophilic N-Alkylindoles to Styrenes by Photoredox Catalysis
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The consecutive addition of acyl radicals and N-alkylindole nucleophiles to styrenes was established, as well as some additional radical-nucleophile combinations. Both aryl and aliphatic aldehydes give reasonable yields. The reaction proceeds best for α-substituted styrenes, effectively creating a quaternary all-carbon center. Some iridium-based photoredox systems are catalytically active; furthermore, a base is needed in this transformation. Radicals are formed by reductive perester cleavage and hydrogen atom transfer.
- Klussmann, Martin,Lux, Marcel
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supporting information
(2020/04/30)
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- Ascorbic Acid as an Aryl Radical Inducer in the Gold-Mediated Arylation of Indoles with Aryldiazonium Chlorides
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In recent years interest in the development of protocols that facilitate the oxidative addition of gold to access mild cross-coupling processes mediated by this metal has increased. In this context, we report herein that ascorbic acid, a natural and readily accessible antioxidant, can be used to accelerate the oxidative addition of aryldiazonium chlorides onto AuI. The aryl–AuIII species generated in this way, has been used to prepare 3-arylindoles in a one-pot protocol starting from anilines and para-, meta-, and ortho- substituted aryldiazonium chlorides. The mechanism underlying the oxidative addition has been examined in detail based on EPR analyses, cyclic voltammetry, and DFT calculations. Interestingly, we have found that in this protocol, the chloride atom induces the AuII/AuIII oxidation step.
- Medina-Mercado, Ignacio,Asomoza-Solís, Eric Omar,Martínez-González, Eduardo,Ugalde-Saldívar, Victor Manuel,Ledesma-Olvera, Lydia Gabriela,Barquera-Lozada, José Enrique,Gómez-Vidales, Virginia,Barroso-Flores, Joaquín,Frontana-Uribe, Bernardo A.,Porcel, Susana
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supporting information
p. 634 - 642
(2019/12/11)
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- Synthesis of Cyclopenta[b]indoles via a Formal [3+2] Cyclization of N-Sulfonyl-1,2,3-triazoles and Indoles
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Annulation of benzoxy-tethered N-sulfonyl-1,2,3-triazoles and indoles has been developed in this paper, providing an efficient and convenient access to valuable cyclopenta[b]indoles in moderate to good yields. α,β-Unsaturated imine, which generated in situ from denitrogenation and 1,2-OBz migration of triazole, provided three carbons for the formal [3+2] cyclization reaction for the first time. (Figure presented.).
- Duan, Shengguo,Zhang, Wan,Hu, Yuntong,Xu, Ze-Feng,Li, Chuan-Ying
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supporting information
p. 3570 - 3575
(2020/08/05)
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- Tridentate Nickel(II)-Catalyzed Chemodivergent C-H Functionalization and Cyclopropanation: Regioselective and Diastereoselective Access to Substituted Aromatic Heterocycles
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A Schiff-base nickel(II)-phosphene-catalyzed chemodivergent C-H functionalization and cyclopropanation of aromatic heterocycles is reported in moderate to excellent yields and very good regioselectivity and diastereoselectivity. The weak, noncovalent interaction between the phosphene ligand and Ni center facilitates the ligand dissociation, generating the electronically and coordinatively unsaturated active catalyst. The proposed mechanisms for the reported reactions are in good accord with the experimental results and theoretical calculations, providing a suitable model of stereocontrol for the cyclopropanation reaction.
- Nag, Ekta,Gorantla, Sai Manoj N. V. T.,Arumugam, Selvakumar,Kulkarni, Aditya,Mondal, Kartik Chandra,Roy, Sudipta
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supporting information
p. 6313 - 6318
(2020/09/02)
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- Detosylative (Deutero)alkylation of Indoles and Phenols with (Deutero)alkoxides
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An efficient strategy for N/O-(deutero)alkylation of indoles and phenols with alkoxides/alcohols as the alkylation reagents is described. The consecutive detosylation/alkylation transformations feature mild reaction conditions, high ipso-selectivity, and good functional group tolerance (>50 examples). A one-pot selective N-alkylation of unprotected indoles with alcohols and TsCl is also realized. The application of this method is demonstrated by the introduction of isotope-labeled (CD3 and 13CH3) groups using the readily accessible labeled alcohols and the synthesis of pharmaceuticals.
- Zhu, Ming-Hui,Yu, Cheng-Long,Feng, Ya-Lan,Usman, Muhammad,Zhong, Dayou,Wang, Xin,Nesnas, Nasri,Liu, Wen-Bo
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supporting information
p. 7073 - 7077
(2019/09/30)
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- Replacement of Stoichiometric DDQ with a Low Potential o-Quinone Catalyst Enabling Aerobic Dehydrogenation of Tertiary Indolines in Pharmaceutical Intermediates
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A transition-metal/quinone complex, [Ru(phd)3]2+ (phd = 1,10-phenanthroline-5,6-dione), is shown to be effective for aerobic dehydrogenation of 3° indolines to the corresponding indoles. The results show how low potential quinones may be tailored to provide a catalytic alternative to stoichiometric DDQ, due to their ability to mediate efficient substrate dehydrogenation while also being compatible with facile reoxidation by O2. The utility of the method is demonstrated in the synthesis of key intermediates to pharmaceutically important molecules.
- Li, Bao,Wendlandt, Alison E.,Stahl, Shannon S.
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supporting information
p. 1176 - 1181
(2019/02/14)
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- Photocatalytic Alkylation of Pyrroles and Indoles with α-Diazo Esters
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This article describes the photoalkylation of electron-rich aromatic compounds with diazo esters. C-2-alkylated indoles and pyrroles are obtained with good yields even though the photocatalyst loading is as low as 0.075 mol %. For EWG-substituted substrates, the addition of a catalytic amount of N,N-dimethyl-4-methoxyaniline is required. Both EWG-EWG- and EWG-EDG-substituted diazo esters are suitable as alkylating agents. The reaction selectivity and mechanistic experiments suggest that carbenes/carbenoid intermediates are not involved in the reaction pathway.
- Ciszewski, Lukasz W.,Durka, Jakub,Gryko, Dorota
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supporting information
p. 7028 - 7032
(2019/09/12)
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- Switchable regioselection of C-H thiolation of indoles using different TMS counterions
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A switchable regioselectivity in C-H thiolation reaction by simply swapping the counteranions of TMS is reported here for the first time. An exclusive C3-H thiolation of indoles with sodium arylsulfinates was achieved in the presence of TMSCl as a promoter. In contrast, with the use of TMSOTf instead of TMSCl under otherwise identical conditions, a regiospecific C2-H thiolation of indoles was realized with the same set of substrates.
- Ji, Yuan-Zhao,Li, Hui-Jing,Zhang, Jin-Yu,Wu, Yan-Chao
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supporting information
p. 11864 - 11867
(2019/10/11)
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- Cu-Catalyzed Oxidation of C2 and C3 Alkyl-Substituted Indole via Acyl Nitroso Reagents
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The selective oxidation of C2-alkyl-substituted indoles to 3-oxindole and the selective C-H oxygenation or amination of C2,C3-dialkyl-substituted indoles at C2 are reported under mild conditions. The position of the alkyl substitution on the indole directs the reaction to different pathways under similar conditions.
- Zhang, Jun,Torabi Kohlbouni, Saeedeh,Borhan, Babak
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supporting information
p. 14 - 17
(2019/01/08)
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- Synthesis of 3-Formylindoles via Electrochemical Decarboxylation of Glyoxylic Acid with an Amine as a Dual Function Organocatalyst
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A new method for 3-formalytion of indoles has been developed through electrochemical decarboxylation of glyoxylic acid with the amine as a dual function organocatalyst. The amine facilitated both the electrochemical decarboxylation and the nucleophilic reaction efficiently, whose loading can be as low as 1 mol %. This protocol has a broad range of functional group tolerance under ambient conditions. The gram-scale experiment has shown great potential in the synthetic application of this strategy.
- Lin, Dian-Zhao,Huang, Jing-Mei
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supporting information
p. 5862 - 5866
(2019/08/26)
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- Site-Selective 1,1-Difunctionalization of Unactivated Alkenes Enabled by Cationic Palladium Catalysis
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A palladium(II)-catalyzed 1,1-difunctionalization of unactivated terminal and internal alkenes via addition of two nucleophiles was developed using a cationic palladium(II) complex. The palladacycle generated in situ as a result of a regioselective addition of a nucleophile to the alkene can readily undergo regioselective β-hydride elimination and migratory insertion with a cationic palladium catalyst. The resulting η3-π-allyl palladium(II) complex is the key intermediate that reacts with a second nucleophile to furnish the desired 1,1-difunctionalization of the alkene. Under the optimized reaction conditions, a wide range of indoles and anilines add to alkene units of 3-butenoic or 4-pentenoic acid derivatives to afford the synthetically useful γ,γ- or δ,δ-difunctionalized products with excellent regiocontrol. Furthermore, by employing internal hydroxyl or acid groups and external carbon nucleophiles, this transformation enables unsymmetric 1,1-difunctionalization to forge challenging and important oxo quaternary carbon centers. Combining experiments and DFT calculations on the mechanism of the reaction is investigated in detail.
- Jeon, Jinwon,Ryu, Ho,Lee, Changseok,Cho, Dasol,Baik, Mu-Hyun,Hong, Sungwoo
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supporting information
(2019/07/03)
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- Site-Selective 1,1-Difunctionalization of Unactivated Alkenes Enabled by Cationic Palladium Catalysis
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A palladium(II)-catalyzed 1,1-difunctionalization of unactivated terminal and internal alkenes via addition of two nucleophiles was developed using a cationic palladium(II) complex. The palladacycle generated in situ as a result of a regioselective addition of a nucleophile to the alkene can readily undergo regioselective β-hydride elimination and migratory insertion with a cationic palladium catalyst. The resulting η 3-π-allyl palladium(II) complex is the key intermediate that reacts with a second nucleophile to furnish the desired 1,1-difunctionalization of the alkene. Under the optimized reaction conditions, a wide range of indoles and anilines add to alkene units of 3-butenoic or 4-pentenoic acid derivatives to afford the synthetically useful γ,γ-or ?,?-difunctionalized products with excellent regiocontrol. Furthermore, by employing internal hydroxyl or acid groups and external carbon nucleophiles, this transformation enables unsymmetric 1,1-difunctionalization to forge challenging and important oxo quaternary carbon centers. Combining experiments and DFT calculations on the mechanism of the reaction is investigated in detail.
- Jeon, Jinwon,Ryu, Ho,Lee, Changseok,Cho, Dasol,Baik, Mu-Hyun,Hong, Sungwoo
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supporting information
p. 10048 - 10059
(2019/07/04)
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- Electrochemically Enabled C3-Formylation and -Acylation of Indoles with Aldehydes
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Reported herein is an effective strategy for oxidative cross-coupling of indoles with various aldehydes. The strategy is based on a two-step transformation via a well-known Mannich-type reaction and a C-N bond cleavage for carbonyl introduction. The key step - the C-N bond cleavage of the Mannich product - was enabled by electrochemistry. This strategy (with over 40 examples) ensures excellent functional-group tolerance as well as late-stage functionalization of pharmaceutical molecules.
- Yang, Liquan,Liu, Zhaoran,Li, Yujun,Lei, Ning,Shen, Yanling,Zheng, Ke
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supporting information
p. 7702 - 7707
(2019/10/19)
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- Exploration and Development of a C-H-Activated Route to Access the [1,2]Dithiolo[4,3- b ]indole-3(4 H)-thione Core and Related Derivatives
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A robust procedure for the production of [1,2]dithiolo[4,3- b ]indole-3(4 H)-thione analogues using a DABCO/S 2 Cl 2 complex as a sulfur source via a C-H activated approach.
- Asquith, Christopher R. M.,Konstantinova, Lidia S.,Tizzard, Graham J.,Laitinen, Tuomo,Coles, Simon J.,Rakitin, Oleg A.,Hilton, Stephen T.
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p. 156 - 160
(2019/01/14)
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- Tryptamine Synthesis by Iron Porphyrin Catalyzed C?H Functionalization of Indoles with Diazoacetonitrile
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The functionalization of C?H bonds with non-precious metal catalysts is an important research area for the development of efficient and sustainable processes. Herein, we describe the development of iron porphyrin catalyzed reactions of diazoacetonitrile with N-heterocycles yielding important precursors of tryptamines, along with experimental mechanistic studies and proof-of-concept studies of an enzymatic process with YfeX enzyme. By using readily available FeTPPCl, we achieved the highly efficient C?H functionalization of indole and indazole heterocycles. These transformations feature mild reaction conditions, excellent yields with broad functional group tolerance, can be conducted on gram scale, and thus provide a unique streamlined access to tryptamines.
- Hock, Katharina J.,Knorrscheidt, Anja,Hommelsheim, Renè,Ho, Junming,Weissenborn, Martin J.,Koenigs, Rene M.
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supporting information
p. 3630 - 3634
(2019/02/13)
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- Pd-Catalyzed Dearomative Carboxylation of Indolylmethanol Derivatives
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By using a new catalytic system (PdCl2[P(n-Bu)3]2 in combination with ZnEt2), various 3-indolylmethanol derivatives were successfully carboxylated with CO2 (1 atm) via dearomatization of the indole nucleus, affording 3-methyleneindoline-2-carboxylates. In contrast, carboxylation of 2-indolylmethanol derivatives afforded unexpected doubly carboxylated products, which are useful synthetic precursors for biologically active compounds.
- Mita, Tsuyoshi,Ishii, Sho,Higuchi, Yuki,Sato, Yoshihiro
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supporting information
p. 7603 - 7606
(2018/12/11)
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- Decarbonylative Methylation of Aromatic Esters by a Nickel Catalyst
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A Ni-catalyzed decarbonylative methylation of aromatic esters was achieved using methylaluminums as methylating agents. Dimethylaluminum chlorides uniquely worked as the methyl source. Because of the Lewis acidity of aluminum reagents, less reactive alkyl esters could also undergo the present methylation. By controlling the Lewis acidity of aluminum reagents, a chemoselective decarbonylative cross-coupling between alkyl esters and phenyl esters was successful.
- Okita, Toshimasa,Muto, Kei,Yamaguchi, Junichiro
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p. 3132 - 3135
(2018/05/28)
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- Metal-Free Oxidative Cross Coupling of Indoles with Electron-Rich (Hetero)arenes
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A new method for the synthesis of bi-heteroaryls is reported, based on the umpolung of indoles with benziodoxol(on)e hypervalent iodine reagents (IndoleBX). The oxidative coupling of IndoleBX with an equimolar amount of electron-rich benzenes, indoles, pyrroles, and thiophenes proceeded under mild transition-metal-free conditions. Functionalized non-symmetrical bi-indolyl heterocycles were accessed efficiently. Introduction of a new type of C2-substituted indole benziodoxole reagents further allowed extending the scope of the reaction to NH unprotected and C3-alkylated indoles. The obtained bi-heterocycles are important building blocks in synthetic and medicinal chemistry, and could be easily transformed into more complex heterocyclic systems.
- Caramenti, Paola,Nandi, Raj Kumar,Waser, Jerome
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supporting information
p. 10049 - 10053
(2018/07/29)
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- Directly Bridging Indoles to 3,3′-Bisindolylmethanes by Using Carboxylic Acids and Hydrosilanes under Mild Conditions
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A straightforward Lewis acid-promoted protocol for 3,3′-bisindolylmethanes (BIMs) synthesis by reductive alkylation of indoles at the C3 position with carboxylic acids in the presence of hydrosilane was developed for the first time. Instead of aldehydes, more readily available, stable, and easy-to-handle carboxylic acids have been employed as alternative alkylating agents. As an efficient organocatalyst, B(C6F5)3 enables the reductive alkylation of various substituted indole derivatives with carboxylic acids with up to 98 % yield at room temperature and under neat conditions. This metal-free strategy offers an alternative approach for the direct functionalization of indoles to BIMs with carboxylic acids and such protocol allows selective reduction of carboxylic acid to aldehyde in combination with C?C bond formation.
- Qiao, Chang,Liu, Xiao-Fang,Fu, Hong-Chen,Yang, Hao-Peng,Zhang, Zhi-Bo,He, Liang-Nian
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p. 2664 - 2670
(2018/09/14)
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- Design, synthesis and biological evaluation of novel 2-sulfonylindoles as potential anti-inflammatory therapeutic agents for treatment of acute lung injury
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Acute lung injury (ALI) is primarily driven by inflammation that severely impacts lung function. Novel 2-sulfonylindoles were recently shown to exhibit anti-inflammatory activity through the inhibition of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production. Here, we synthesized 31 compounds which contained 2-sulfonylindole structure. The compounds 8a, 9g, 9h and 9k exhibited dose-dependent anti-inflammatory activity in vitro. Structural-activity relationship analysis revealed that the introduction of sulfonyl group in indole nucleus may be successful to obtain new anti-inflammatory structures and leads. The compounds 9h and 9k also decreased liposaccharide (LPS)-induced IL-6, IL-1β and vascular cell adhesion molecule-1 (VCAM-1) mRNA expression, both in vitro and in an in vivo model of ALI. Furthermore, the compounds 9h and 9k at a high dose (20 mg/kg) significantly protected against LPS-induced ALI in mice. These results show that compounds 9h and 9k could be a promising lead structure for the treatment of ALI.
- Xia, Qinqin,Bao, Xiaodong,Sun, Chuchu,Wu, Di,Rong, Xiaona,Liu, Zhiguo,Gu, Yugui,Zhou, Jianmin,Liang, Guang
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p. 120 - 132
(2018/10/21)
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- Chiral Pincer Carbodicarbene Ligands for Enantioselective Rhodium-Catalyzed Hydroarylation of Terminal and Internal 1,3-Dienes with Indoles
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Catalytic enantioselective addition of N-heteroarenes to terminal and internal 1,3-dienes is reported. Reactions are promoted by 5 mol % of Rh catalyst supported by a new chiral pincer carbodicarbene ligand that delivers allylic substituted arenes in up to 95% yield and up to 98:2 er. Mechanistic and X-ray evidence is presented that supports that the reaction proceeds via a Rh(III)-η3-allyl.
- Marcum, Justin S.,Roberts, Courtney C.,Manan, Rajith S.,Cervarich, Tia N.,Meek, Simon J.
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supporting information
p. 15580 - 15583
(2017/11/14)
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- Indole- and Pyrrole-BX: Bench-Stable Hypervalent Iodine Reagents for Heterocycle Umpolung
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The one-step synthesis of the bench-stable hypervalent iodine reagents IndoleBX and PyrroleBX using mild Lewis acid catalyzed conditions is reported. The new reagents are stable up to 150 °C and were applied in the C?H arylation of unactivated arenes using either rhodium or ruthenium catalysts. A broad range of heterocyclic systems of high interest for synthetic and medicinal chemistry was accessed in high yields. The developed C?H functionalization could not be achieved using reported reagents or methods, highlighting the unique reactivity of Indole- and Pyrrole-BX.
- Caramenti, Paola,Nicolai, Stefano,Waser, Jerome
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supporting information
p. 14702 - 14706
(2017/09/11)
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- Ring-Opening Diarylation of Siloxydifluorocyclopropanes by Ag(I) Catalysis: Stereoselective Construction of 2-Fluoroallylic Scaffold
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A silver-catalyzed, defluorination ring-opening diarylation of siloxy 2,2-difluorocyclopropanes, with two arenes, to directly prepare polysubstituted 2-fluoroallylic compounds, is described. This multicomponent reaction proceeds smoothly in good stereoselectivity, which is due to a chelation-controlled addition of arenes to α-fluorinated ketone intermediate.
- Song, Xiaoning,Xu, Cong,Du, Dongxu,Zhao, Ziming,Zhu, Dongsheng,Wang, Mang
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supporting information
p. 6542 - 6545
(2017/12/26)
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- Isocyanide-Induced Activation of Copper Sulfate: Direct Access to Functionalized Heteroarene Sulfonic Esters
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A novel and direct approach to alkyl/aryl heteroarene sulfonic esters using copper sulfate as the environmentally benign inorganic sulfonation reagent was first realized with the aid of isocyanide. A variety of heterocycles reacted to afford the corresponding sulfonic esters through C?H functionalization. In this transformation, the otherwise inert copper sulfate was unusually activated by an isocyanide and employed as the source of the sulfonic substituents in an unprecedented fashion. The findings suggest that an appropriate activator may liberate the chemical activities of some relatively inert inorganic salts for organic synthesis.
- Hong, Xiaohu,Tan, Qitao,Liu, Bingxin,Xu, Bin
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supporting information
p. 3961 - 3965
(2017/03/27)
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- Gold-catalyzed oxidative couplings of two indoles with one aryldiazo cyanide under oxidant-free conditions
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Gold-catalyzed oxidative couplings of two indoles and one α-cyano gold carbene to form bis(indolyl)methane derivatives are described. Two different indoles are compatible with these reactions to provide reasonable yields. A plausible mechanism is postulated to rationalize the experimental data including product distributions, D2O labeling, and the significant effects of gold catalysts and cyano groups.
- Singh, Rahulkumar Rajmani,Liu, Rai-Shung
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supporting information
p. 4593 - 4596
(2017/04/28)
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- Copper-mediated trifluoroacetylation of indoles with ethyl trifluoropyruvate
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Direct trifluoroacetylation of indoles with ethyl trifluoropyruvate as a trifluoroacetylating reagent has been developed. This novel protocol provides an attractive route for the preparation of 3-trifluoroacetylindole derivatives, due to its operational simplicity and practicability as well as mild reaction conditions.
- Yan, Guobing,Cao, Xihan,Zheng, Wanbin,Ke, Qiumin,Zhang, Jieyu,Huang, Dayun
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supporting information
p. 5904 - 5907
(2017/07/25)
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- Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles
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An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X-ray crystal analysis, and by quantum-mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate-determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.
- Maier, Alexander F. G.,Tussing, Sebastian,Schneider, Tobias,Fl?rke, Ulrich,Qu, Zheng -Wang,Grimme, Stefan,Paradies, Jan
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p. 12219 - 12223
(2016/10/13)
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- Electronic Nature of Ketone Directing Group as a Key to Control C-2 vs C-4 Alkenylation of Indoles
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A novel mode of achieving site selectivity between C-2 and C-4 positions in the indole framework by altering the property of the ketone directing group is disclosed. Methyl ketone, as directing group, furnishes exclusively C-2 alkenylated product, whereas trifluoromethyl ketone changes the selectivity to C-4, indicating that the electronic nature of the directing group controls the unusual choice between a 5-membered and a 6-membered metallacycle. The screening of other carbonyl-derived directing groups reveals that strong and weak directing groups exhibit opposite selectivity. Experimental controls and deuteration experiments lend support to the proposed mechanism.
- Lanke, Veeranjaneyulu,Bettadapur, Kiran R.,Prabhu, Kandikere Ramaiah
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supporting information
p. 5496 - 5499
(2016/11/17)
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- Structure and Reactivity of Indolylmethylium Ions: Scope and Limitations in Synthetic Applications
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Eight substituted aryl(indol-3-yl)methylium tetrafluoroborates 3(a-h)-BF4 and three bis(indol-3-yl)methylium tetrafluoroborates 3(i-k)-BF4 have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Their reactions with π-nucleophiles 8(a-j) (silylated enol ethers and ketene acetals) were studied kinetically using photometric monitoring at 20 °C. The resulting second-order rate constants were found to follow the correlation log k(20 °C) = sN(N + E), in which nucleophiles are characterized by the two solvent-dependent parameters N and sN, and electrophiles are characterized by one parameter, E. From the previously reported N and sN parameters of the employed nucleophiles and the measured rate constants, the electrophilicities of the indol-3-ylmethylium ions 3(a-k) were derived and used to predict potential nucleophilic reaction partners. A discrepancy between published rate constants for the reactions of morpholine and piperidine with the (2-methylindol-3-yl)phenylmethylium ion 3h and those calculated from E, N, and sN was analyzed and demonstrated to be due to a mistake of the value reported in the literature.
- Follet, Elsa,Berionni, Guillaume,Mayer, Peter,Mayr, Herbert
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p. 8643 - 8656
(2015/09/15)
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- Probing the molecular and structural elements of ligands binding to the active site versus an allosteric pocket of the human farnesyl pyrophosphate synthase
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In order to explore the interactions of bisphosphonate ligands with the active site and an allosteric pocket of the human farnesyl pyrophosphate synthase (hFPPS), substituted indole and azabenzimidazole bisphosphonates were designed as chameleon ligands. NMR and crystallographic studies revealed that these compounds can occupy both sub-pockets of the active site cavity, as well as the allosteric pocket of hFPPS in the presence of the enzyme's Mg2+ ion cofactor. These results are consistent with the previously proposed hypothesis that the allosteric pocket of hFPPS, located near the active site, plays a feed-back regulatory role for this enzyme.
- Gritzalis, Dimitrios,Park, Jaeok,Chiu, Wei,Cho, Hyungjun,Lin, Yih-Shyan,De Schutter, Joris W.,Lacbay, Cyrus M.,Zielinski, Michal,Berghuis, Albert M.,Tsantrizos, Youla S.
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supporting information
p. 1117 - 1123
(2015/02/19)
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- Synthesis of indoles through Rh(III)-catalyzed C-H cross-coupling with allyl carbonates
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A practical Rh-catalyzed reaction was developed to achieve 2-alkyl-substituted indole synthesis. The reaction can tolerate a variety of synthetically important functional groups. The indole products can also be transformed into other important skeletons. Two bioactive compounds, that is indomethacin and pravadoline were prepared using the new method.
- Gong, Tian-Jun,Cheng, Wan-Min,Su, Wei,Xiao, Bin,Fu, Yao
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p. 1859 - 1862
(2014/03/21)
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- Mild aminoacylation of indoles and pyrroles through a three-component reaction with ynol ethers and sulfonyl azides
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An effective method for aminoacylation of indoles and pyrroles has been achieved. The transformation involves a multicomponent one-pot cascade reaction between indoles or pyrroles, ynol ethers, and sulfonyl azides, creating four different bonds regioselectively through N-sulfonyltriazole intermediates. The oxo-tryptamines and oxo-pyrroloethanamines are generated in moderate to high yields under mild reaction conditions.
- Alford, Joshua S.,Davies, Huw M. L.
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supporting information
p. 10266 - 10269
(2014/08/05)
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- New reactions of N-tert-butylimines; Formation of N-heterocycles by methyl radical elimination on flash vacuum thermolysis of N-benzylidene- and N-(2-pyridylmethylidene)-tert-butylamines
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Thermal reactions of N-benzylidene- and N-(2-pyridylmethylidene)-tert- butylamines (5 and 13) under FVT conditions have been investigated. Unexpectedly, at 800 °C, compound 5 yields 1,2-dimethylindole and 3-methylisoquinoline. In the reaction of 13 at 800 °C, 3-methylimidazo[1,5- a]pyridine was obtained as the major product. Mechanisms of these reactions have been proposed on the basis of DFT calculations. Furthermore, UV-photoelectron spectroscopy combined with FVT has been applied for direct monitoring and characterization of the thermolysis products in situ. Copyright
- Vu, Thien Y,Chrostowska, Anna,Huynh, Thi Kieu Xuan,Khayar, Said,Dargelos, Alain,Justyna, Katarzyna,Pasternak, Beata,Lesniak, Stanislaw,Wentrup, Curt
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supporting information
p. 14983 - 14988
(2013/11/06)
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- Copper-promoted decarboxylative direct C3-acylation of N-substituted indoles with α-oxocarboxylic acids
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A novel and efficient Cu-promoted decarboxylative direct C3-acylation of N-substituted indoles with α-oxocarboxylic acids for the synthesis of 3-acylindoles was developed. The Royal Society of Chemistry.
- Yu, Lin,Li, Pinhua,Wang, Lei
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supporting information
p. 2368 - 2370
(2013/06/27)
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- Catalytic generation of borenium ions by cooperative B-H bond activation: The elusive direct electrophilic borylation of nitrogen heterocycles with pinacolborane
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The B-H bond of typical boranes is heterolytically split by the polar Ru-S bond of a tethered ruthenium(II) thiolate complex, affording a ruthenium(II) hydride and borenium ions with a dative interaction with the sulfur atom. These stable adducts were spectroscopically characterized, and in one case, the B-H bond activation step was crystallographically verified, a snapshot of the σ-bond metathesis. The borenium ions derived from 9-borabicyclo[3.3.1] nonane dimer [(9-BBN)2], pinacolborane (pinBH), and catecholborane (catBH) allowed for electrophilic aromatic substitution of indoles. The unprecedented electrophilic borylation with the pinB cation was further elaborated for various nitrogen heterocycles.
- Stahl, Timo,Muether, Kristine,Ohki, Yasuhiro,Tatsumi, Kazuyuki,Oestreich, Martin
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supporting information
p. 10978 - 10981
(2013/08/23)
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- Visible light-induced 3-sulfenylation of N-methylindoles with arylsulfonyl chlorides
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The synthesis of 1-methyl-3-(arylthio)-1H-indoles has been achieved by the photoredox reaction of N-methylindoles with readily available arylsulfonyl chlorides in moderate yields.
- Chen, Min,Huang, Zhi-Tang,Zheng, Qi-Yu
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supporting information
p. 11686 - 11688,3
(2012/12/12)
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