- Mild and Practical Indole C2 Allylation by Allylboration of in situ Generated 3-Chloroindolenines
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C2 allylation of indole derivatives is a challenging but important transformation given the biological relevance of the products. Herein we report a selective C2 allylation strategy that proceeds via allylboration of in situ-generated 3-chloroindolenines. The reaction is mild, practical, and compatible with a wide range of C3-substituted indoles. As allylboronates are readily accessible from commercial precursors, various substituted allyl moieties can be introduced using the same protocol. To showcase the utility of this method we applied it to the synthesis of the natural product, tryprostatin B.
- Saya, Jordy M.,van Wordragen, Ellen D. H.,Orru, Romano V. A.,Ruijter, Eelco
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p. 5156 - 5160
(2019/01/25)
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- PdBr2-catalyzed direct synthesis of 2,3-disubstituted indoles via a tandem reaction between arylamines and α-diketones
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A direct PdBr2(BINAP)-complex catalyzed method has been developed to produce 2,3-disubstituted indoles by the reaction of arylamines with α-diketones under reductive (H2) conditions. The synthetic methodology involves a tandem reaction of three steps and all the organic intermediates were isolated and characterized, the reduction products in this sequence are chiral and present interesting enantiomeric excess. This report constitutes a new and different route to synthesize indoles and a plausible mechanism is also suggested.
- Cabrera,Sharma,Ayala,Rubio-Perez,Amézquita-Valencia, Manuel
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supporting information; experimental part
p. 6758 - 6762
(2012/01/04)
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- Efficient synthesis of 2-mono and 2,3-disubstituted indoles via palladium-catalyzed oxidation of aminoalcohols
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Efficient synthesis of 2-mono- and 2,3-disubstituted indoles has been accomplished via palladium-catalyzed oxidation of aminoalcohols.
- Aoyagi, Yutaka,Shishikura, Masahiro,Mizusaki, Toshihiko,Komine, Takashi,Yoshinaga, Tokuji,Inaba, Haruko,Ohta, Akihiro,Takeya, Koichi
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p. 1055 - 1059
(2008/12/20)
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- Zeolites as Catalysts in the Fischer Indole Synthesis. Enhanced Regioselectivity for Unsymmetrical Ketone Substrates
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The use of zeolites as catalysts in the Fischer indole synthesis has been studied on five unsymmetrical ketone substrates with 14 different zeolites.Both the corresponding phenylhydrazone and the parent ketone in the presence of phenylhydrazine were used as substrates.Zeolites which catalysed the indolization of the phenylhydrazones were also active in the direct conversion of the parent ketone.For substrates which gave mixtures of isomeric indoles under homogeneous, classical indolization conditions in acetic acid, it was found that the distribution of regioisomersof the indoles formed was altered considerably by zeolite catalysis and that the distribution was dependent on the type of zeolite used.A one-pot synthetic procedure for indole synthesis from the parent ketone and phenylhydrazine is described.
- Prochazka, Michal P.,Eklund, Lars,Carlson, Rolf
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p. 610 - 613
(2007/10/02)
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- One-Pot Fischer Indole Synthesis by Zeolite Catalysis
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A one-pot procedure for the synthesis of substituted indoles by heating the parent ketone and a phenylhydrazine in the presence of an acid zeolite catalyst is described.Using 3-hexanone as a unsymmetrical model ketone and a para-substituted phenylhydrazine as the co-reagent (H, NO2, MeO, Cl as substituents) it was found that the ratio of the possible regioisomers of the indoles is highly dependent on the type of zeolite used as the catalyst.Isolated yields of the indoles were in the range 54-98percent.It is also shown that zeolites can be used as catalysts in a flow-reactor system to achieve indole synthesis.
- Prochazka, Michal P.,Carlson, Rolf
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p. 614 - 616
(2007/10/02)
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- On the Role of Lewis Acid Catalysts and Solvents in the Fischer Indole Synthesis
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The influence of the Lewis acid catalyst and solvent on the Fischer indole reaction has been studied with regard to the distribution of indole isomers in the reaction of phenylhydrazones derived from unsymmetrical ketones.Five ketones, ten solvents and twelve Lewis acids were studied.A multivariate experimental design based on the principal pproperties of the reactants was used to select test systems (substrate, Lewis acid, solvent).A total of 296 of different systems were studied, of which 162 afforded indoles.Analysis of how the properties of these systems are related to the distribution of isomeric indoles was done by PLS modeling.A three-components model was significant according to cross validation and described 87percent of the variance of the isomer distribution.The model showed that the structure of the phenylhydrazone has a dominant influence on isomer distribution; that solvent properties are only wealky involved; and that the properties of the Lewis acid catalyst does not exert any systematic influence on the regioselectivity of the Fischer indole reaction.
- Prochazka, Michal P.,Carlson, Rolf
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p. 651 - 659
(2007/10/02)
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- Regioselective Indolization of Unsymmetrical Phenylhydrazones by Reaction, at Room Temperature, with PCl3
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Unsymmetrical ketone phenylhydrazones (1) (R1 ae R2) react with PCl3, at room temperature to give predominantly one, (2), of the two possible 2,3-disubstituted indoles in good to excellent overall yield.When the R1 and R2 groups are very different (R1 = Ph or Me; R2 = alkyl or H) the reaction is highly regioselective leading to exclusive or prevalent formation of the corresponding 3-R1 indoles (2), whereas when R1 and R2 are very similar (R1, R2 = alkyl chains) the regioselectivity is decreased and the indole having the shorter chain in the 3-position predominates, but only slightly.Inspection of the results enables the direction of indolization to be predicted and the positions of the substituents in the 2,3-disubstituted indoles to be assigned with certainty, features not inherent in the classical Fischer indolization.
- Baccolini, Graziano,Bartoli, Giuseppe,Marotta, Emanuela,Todesco, Paolo E.
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p. 2695 - 2697
(2007/10/02)
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- C-2 SIDE CHAIN ALKYLATION OF 2-METHYL-3-ALKYLINDOLES VIA 3-METHOXYINDOLENINES
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3-Methoxyindolenines derived from 2-methyl-3-alkylindoles by bromination-methanolysis undergo base induced alkylation and aldol condensations at the C-2 methyl group.The modified indolenines can be efficiently converted to C-2-side chain alkylated indoles
- Vice, Susan F.,Gross, Edward A.,Friesen, Richard W.,Dmitrienko, Gary I.
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p. 829 - 832
(2007/10/02)
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- Palladium-Assisted N-Alkylation of Indoles: Attempted Application to Polycyclization
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The palladium(II) complexes of the olefins ethene, propene, and 1-hexene reacted with 1-lithioindole to produce N-alkylated indoles exclusively.Attempts to perform this N-alkylation intramoleculary (to form tricyclic material from 2-allylskatole) failed.Anilines with dienic side chains in the 2-position were subjected to Pd(II)-assisted cyclization conditions in attempts to induce polycyclization.However, only monocyclization was observed.
- Hegedus, Louis S.,Winton, Peter M.,Varaprath Sudarsanan
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p. 2215 - 2221
(2007/10/02)
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