- Nickel-Catalyzed Straightforward and Regioselective C-H Alkenylation of Indoles with Alkenyl Bromides: Scope and Mechanistic Aspect
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Nickel-catalyzed regioselective C-H bond alkenylation of indoles and related heteroarenes with alkenyl bromides is accomplished under relatively mild conditions. This method allows the straightforward synthesis of C-2 alkenylated indoles employing an air-stable and well-defined nickel catalyst, (bpy)NiBr2, providing a solution to the limitations associated with hydroindolation and oxidative alkenylation. The reaction conceded the coupling of indole derivatives with various alkenyl bromides, such as aromatic and heteroaromatics, α- and β-substituted as well as exo- and endo-cyclic alkenyl compounds. An extensive mechanistic investigation, including controlled study, reactivity experiments, kinetics and labeling studies, and EPR and XPS analyses, highlights that the alkenylation proceeds through a single-electron transfer process comprising an odd-electron oxidative addition of alkenyl bromide. Furthermore, the alkenylation operates via a probable Ni(I)/Ni(III) pathway involving the rate-limiting C-H nickelation of indole.
- Jagtap, Rahul A.,Vinod,Punji, Benudhar
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- Organocatalytic diels-alder reaction of 2-vinylindoles with methyleneindolinones: An efficient approach to functionalized carbazolespirooxindoles
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An unprecedented asymmetric Diels-Alder reaction of 2-vinylindoles with methyleneindolinones has been disclosed. Under bifunctional organocatalysis by cinchona-derived squaramide catalyst, a series of diversely functionalized carbazolespirooxindole derivatives bearing three contiguous stereocenters are rapidly constructed under mild conditions (48-90% yields, up to >20:1 dr and 99% ee).
- Huang, Lin-Jie,Weng, Jiang,Wang, Sheng,Lu, Gui
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- Rhodium-Catalyzed Aryl Migratory/Decarbonylation of Diaryl Ketones via the Activation of Unstrained C-C Bonds
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A Rh-catalyzed aryl migratory/decarbonylation of unstrained ketones has been developed. This viable transformation provides a complementary decarbonylative method using diaryl ketones to afford a variety of alkenylated heterocycles in good yields with moderate to good stereoselectivity and broad substrate scope. The synthetic utility of this protocol is also demonstrated by the conversion of the alkenylated heterocycles to tetrahydrocarbazole derivatives.
- Yu, Tian-Yang,Lu, Hong,Shao, Peng-Cheng,Qi, Xiu-Juan,Wei, Hao
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p. 124 - 132
(2021/09/08)
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- One-Pot Reaction between N-Tosylhydrazones and 2-Nitrobenzyl Bromide: Route to NH-Free C2-Arylindoles
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A one-pot Barluenga coupling between N-tosylhydrazones and nitro-benzyl bromide, followed by deoxygenation of ortho-nitrostyrenes, and subsequent cyclization has been developed, providing a new way to synthesize various C2-arylindoles. This method exhibits a good substrate scope and functional group tolerance, and it allows an access to NH-free indoles, which can present a potential utility in medicinal chemistry applications.
- Bzeih, Tourin,Zhang, Kena,Khalaf, Ali,Hachem, Ali,Alami, Mouad,Hamze, Abdallah
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p. 228 - 238
(2019/01/04)
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- Cobalt(III)?Catalyzed C?H Activation: A Secondary Amide Directed Decarboxylative Functionalization of Alkynyl Carboxylic Acids Wherein Amide NH-group Remains Unreactive
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A Co(III)-catalyzed C?H activation reaction for ortho-alkenylation of benzamides (aryl/heteroaryl) and C2-alkenylation of indole derivatives have been developed using alkynyl carboxylic acid as an alkene source. A high regioselectivity has been achieved i
- Muniraj, Nachimuthu,Prabhu, Kandikere Ramaiah
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p. 1370 - 1375
(2018/02/14)
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- Benzannulation of 2-Alkenylindoles using Aldehydes by Sequential Triple-Relay Catalysis: A Route to Carbazoles and Carbazole Alkaloids
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Benzannulation of 2-alkenylindoles with readily available aldehydes, under one-pot sequential triple-relay-catalysis, provides an easy access to several structurally unique carbazoles including 2- and 3-alkenylcarbazoles. This protecting group-free method enabled one-pot synthesis of alkaloids such as hyellazole and 6-chlorohyellazole, and the formal syntheses of seven other alkaloids. Construction of the core structure, present in murastifoline A, murrafoline E, and related alkaloids was also demonstrated. Even conjugated 3,3′-biscarbazoles can also be synthesized by one-pot, two-fold sequential triple-relay catalysis. (Figure presented.).
- Banerjee, Ankush,Sahu, Samrat,Maji, Modhu Sudan
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supporting information
p. 1860 - 1866
(2017/06/09)
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- A Scalable Method for Regioselective 3-Acylation of 2-Substituted Indoles under Basic Conditions
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Privileged structures such as 2-arylindoles are recurrent molecular scaffolds in bioactive molecules. We here present an operationally simple, high yielding and scalable method for regioselective 3-acylation of 2-substituted indoles under basic conditions
- Johansson, Henrik,Urruticoechea, Andoni,Larsen, Inna,Sejer Pedersen, Daniel
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p. 471 - 481
(2015/08/25)
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- Palladium-catalyzed α-arylation of enones in the synthesis of 2-alkenylindoles and carbazoles
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A new unified strategy has been developed for the synthesis of substituted 2-alkenylindoles and carbazoles. The strategy uses palladium-catalyzed α-arylation of TES-enol ethers of enones as the key step. The method is highly regioselective, provides good yields, and is expected to have wide application.
- Kale, Ajit Prabhakar,Kumar, Gangam Srikanth,Mangadan, Arun Raj Kizhakkayil,Kapur, Manmohan
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supporting information
p. 1324 - 1327
(2015/03/14)
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- Rh(i)-catalyzed decarbonylative direct C2-olefination of indoles with vinyl carboxylic acids
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A general and efficient Rh(i)-catalyzed decarbonylative direct C2-olefination of indoles with vinyl carboxylic acids has been developed. The reaction exhibits excellent functional group tolerance, regioselectivity and stereoselectivity, giving a broad range of C2-alkenylated indoles in good to excellent yields. This journal is
- Zhang, Lingjuan,Qiu, Ruiying,Xue, Xiao,Pan, Yixiao,Xu, Conghui,Wang, Doudou,Wang, Xinyu,Xu, Lijin,Li, Huanrong
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supporting information
p. 12385 - 12388
(2015/01/08)
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- Synthesis of indole substituted twistenediones from a 2-quinonyl boronic acid
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Indole substituted twistane-like derivatives resulted in a reaction between 3,5-dimethyl-2-quinonyl boronic acid and 2-alkenyl indoles. Their MCPBA oxidation gave 6/6/9 caged systems. Boronic acid acts as a temporal promoter allowing a site-selective conjugate addition of the heteroaromatic system to the methyl substituted C-3 quinone carbon, giving an intermediate diene which is regioselectively trapped by intramolecular [4 + 2] cycloaddition.
- Rojas-Martin, Jaime,Veguillas, Marcos,Ribagorda, Maria,Carreno, M. Carmen
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supporting information
p. 5686 - 5689
(2013/12/04)
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- PdII-catalysed C-H functionalisation of indoles and pyrroles assisted by the removable N-(2-pyridyl)sulfonyl group: C2-alkenylation and dehydrogenative homocoupling
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The easily installed and removed N-(2-pyridyl)sulfonyl group exerts complete C2 regiocontrol over the PdII-catalysed C-H alkenylation of indoles and pyrroles, affording the corresponding products in good isolated yields (typically ≥ 70%). A remarkable feature of this catalyst system is that it tolerates a wide variety of substituted alkenes, including conjugated electrondeficient alkenes, styrenes and 1,3- dienes, as well as conjugated 1,1- and 1,2-disubstituted olefins. The final reductive desulfonylation affords the C2- substituted, free-NH indoles and pyrroles in good yield. This N-(2-pyridyl)- sulfonyl-directing strategy has also been extended to the development of a protocol for the intermolecular, dehydrogenative homocoupling of indoles, providing 2,2'-biindoles. Mechanistic work based upon reactions with isotopically labelled starting materials and competitive kinetic studies of electronically varied substrates suggests a chelation- assisted electrophilic aromatic substitution palladation mechanism.
- Garcia-Rubia, Alfonso,Urones, Beatriz,Arrayas, Ramon Gomez,Carretero, Juan Carlos
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supporting information; experimental part
p. 9676 - 9685
(2010/10/18)
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- A highly selective tandem cross-coupling of gem-dihaloolefins for a modular, efficient synthesis of highly functionalized indoles
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(Chemical Equation Presented) A highly efficient method of indole synthesis using gem-dihalovinylaniline substrates and an organoboron reagent was developed via a Pd-catalyzed tandem intramolecular amination and an intermolecular Suzuki coupling. Aryl, alkenyl, and alkyl boron reagents are all successfully employed, making for a versatile modular approach. The reaction tolerates a variety of substitution patterns on the aniline leading to indoles with group at C2-C7. The orthogonal approach of the sequential copper- and palladium-mediated synthesis of 1,2-diarylindoles exploited the wide availability of diverse organoboron reagents.
- Fang, Yuan-Qing,Lautens, Mark
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p. 538 - 549
(2008/09/17)
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- 2-SUBSTITUTED INDOLES, THEIR PRECURSORS AND NOVEL PROCESSES FOR THE PREPARATION THEREOF
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Disclosed are processes for the preparation of 2-substituted indole compounds wherein the 2-substituent comprises an R4 group, wherein R4 is selected from the group consisting of monocyclic aromatic, polycyclic aromatic, monocyclic heteroaromatic, polycyclic heteroaromatic, 1° alkyl, and alkenyl, all of which are optionally substituted at one or more substitutable positions with one or more suitable substituents, and wherein R4 is bonded to the 2-position of the indole ring via a C-C bond; the process comprising reacting an ortho-gem-dihalovinylaniline compound of the formula (I): wherein Halo comprises Br, Cl, or I; each of the one or more R1 is independently selected from the group consisting of H, fluoro, lower alkyl, lower alkenyl, lower alkoxy, aryloxy, lower haloalkyl, lower alkenyl, -C(O)O-lower alkyl, monocyclic or polycyclic aryl or heteroaryl moiety, or R1 is an alkenyl group bonded so to as to form a 4- to 20-membered fused monocycle or polycyclic ring with the indole ring; all of which are optionally substituted with one or more suitable substituents at one or more substitutable positions; R2 comprises H, alkyl, cycloalkyl, aryl, heteroaryl, aryl-loweralkyl-, or heteroaryl-loweralkyl-, all of which are optionally substituted at one or more substitutable positions with one or more suitable substituents; R3 comprises H, alkyl, haloalkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, heterocycle, aryl-(C1-6)alkyl-, or heteroaryl-loweralkyl-, all of which are optionally substituted at one or more substitutable positions with one or more suitable substituents; with an organoboron reagent selected from the group consisting of a boronic ester of R4, a boronic acid of R4, a boronic acid anhydride of R4, a trialkylborane of R4 and a 9-BBN derivative of R4; in the presence of a base, a palladium metal pre-catalyst and a ligand under reaction conditions effective to form the 2-substituted indole compound. Also disclosed are processes for the preparation of ortho-gem-dihalovinylaniline compounds. Novel compounds prepared by the processes and novel uses of the compounds are likewise disclosed.
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Page/Page column 64; 101-102
(2010/11/08)
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- Gold(III)-catalyzed annulation of 2-alkynylanilines: A mild and efficient synthesis of indoles and 3-haloindoles
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Gold(III)-catalyzed annulation of 2-alkynylanilines in EtOH or EtOH-water mixtures at room temperature gives indoles derivatives in good yields. One-flask protocol for the gold-catalyzed conversion of 2-alkynylanilines to 3-bromo and 3-iodoindoles is also reported.
- Arcadi, Antonio,Bianchi, Gabriele,Marinelli, Fabio
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p. 610 - 618
(2007/10/03)
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- Radical cyclisation reactions with indoles
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Several radical cyclisation reactions involving indoles are described. Most notably, we have shown that radical additions to C3 of an indole are frequently facile. A dichotomy in the course of radical cyclisation reactions to C2 of the indole has also been exposed wherein 6-endo-trig cyclisations are propagated by the loss of a hydrogen atom from C2 while 5-exo-trig cyclisations are propagated by hydrogen atom abstraction at C3 from tributyltin hydride. Cyclisations involving the addition of indolyl radical intermediates to arenes have also been demonstrated.
- Flanagan, Stuart R.,Harrowven, David C.,Bradley, Mark
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p. 1795 - 1798
(2007/10/03)
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- A simple synthesis of 2-substituted indoles
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A simple preparation of 2-(dimethylaminomethyl)indole, indole-2-acetonitrile and 2-(2-arylvinyl)indoles from 2-methylindole is described.
- Nagarathnam
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p. 743 - 745
(2007/10/02)
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- Studies on the Fischer Indole Synthesis: Rearrangements of Five-, Six- and Seven-membered Cyclic Hydrazones of Pyrazoline, Tetrahydropyridazine and Tetrahydro-1,2-diazepine Series in Polyphosphoric Acid
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The rearrangements of a few cyclic phenylhydrazones structurally related to 1-phenyl-Δ2-pyrazoline, 1-phenyl-1,4,5,6-tetrahydropyridazine, and 1-phenyl-4,5,6,7-tetrahydro-1,2-diazepine in hot polyphosphoric acid (PPA) are described.The five-membered-ring substrates (the pyrazolines) did not undergo the sigmatropic rearrangement typical of the Fischer indolization, the main reaction course being homolytic N-N bond cleavage, leading to benzidine and its 4-(2-benzoylethyl)-4'-(3-phenyl-Δ2-pyrazolin-1-yl) derivative.The six-membered heterocycles underwent two different reactions, both involving the tautomeric enehydrazine form: the first one is the sigmatropic rearrangement, expected for open-chain hydrazones, affording 4-acyl-1,2,3,4-tetrahydroquinoline derivatives; the second one is a retro-Diels-Alder reaction producing methyleneaniline and α,β-unsaturated carbonyl compounds.The seven-membered-ring substrate gave a 5-acyltetrahydrobenzazepine, resulting from the rearrangement, together with both a pyrrolidine and a pyrazine by-product; their formation involves homolytic N-N bond cleavage of the ring, a δ hydrogen abstraction, followed by intramolecular or intermolecular ring closure.Chemical proofs are given for the new structures.
- Benincori, Tiziana,Brenna, Elisabetta,Sannicolo, Franco
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p. 2139 - 2145
(2007/10/02)
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- Selective Wittig Reactions for the Synthesis of Variously Substituted 2-Vinylindoles
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Three selective variants of the Wittig reaction for the syntheses of 2-vinylindoles are described.The reactions are relatively easy to perform, exhibit E-selectivity, and are characterized by a good flexibility with regard to the functional groups present in the vinyl moiety.
- Eitel, Manfred,Pindur, Ulf
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p. 364 - 367
(2007/10/02)
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- SYNTHESIS OF CARBAZOLES VIA 2-VINYLINDOLES.
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2-Vinylindoles are obtained from the Fischer indolization of α,β-unsaturated ketones.Heating 2-(2-methylpropenyl)indole (4) with the Vilsmeier reagent (DMF/POCl3) gave 2-methylcarbazole in good yield, presumably via an electrocyclic ring closure of a hexatrienic intermediate.
- Bergman, J.,Pelcman, B.
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p. 6389 - 6392
(2007/10/02)
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- STUDIES ON THE FISCHER INDOLE SYNTHESIS: BEHAVIOUR OF CYCLIC HYDRAZONES OF TETRAHYDROPYRIDAZINE AND PYRAZOLINE SERIES IN POLYPHOSPHORIC ACID.
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Heating 1,3-diphenyl-1,4,5,6-tetrahydropyridazine in PPA affords mainly 4-benzoyl-1,2,3,4-tetrahydroquinoline and 2-anilinopropiophenone.In analogous conditions 1,5-diphenyl-3-methyl-2-pyrazoline gives 2-styrylindole, benzidine and benzylideneacetone.
- Sannicolo, Franco
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p. 3101 - 3102
(2007/10/02)
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- PALLADIUM(O) AND PHASE TRANSFER CATALYZED CONVERSION OF AZIRINES TO STYRYLINDOLES
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2-Styrylindoles were obtained in modest yields by the exposure of azirines to carbon monoxide, a palladium(O) catalyst, sodium hydroxide, benzene as the organic phase, and benzyltriethylammonium chloride as the phase transfer agent.The reaction is sensitive to the atmosphere used.
- Alper, Howard,Mahatantila, Chulangani P.
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p. 2025 - 2028
(2007/10/02)
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