Thiocyanation of indoles

Treatment of indole, 2-phenylindole, 2-methylindole, and ethyl indole-2-carboxylate with thiocyanogen in acetic acid at 0° afforded the corresponding 3-thiocyanatoindoles in quantitative yields, whereas similar treatment of 3-methyl-2-phenylindoles and 2,3-diphenylindoles gave the corresponding 6-thiocyanatoindoles in high yields.     

Alkylation of indoles

Reaction of indole with tert-butyl chloride in the presence of zinc chloride or acetate gives 3-tert-butylindole, with 1,3-di-tert-butylindole as a by-product.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 620–621, May, 1970.     

Chemistry of indoles

It is shown on the basis of data from the UV and IR spectra that keto acids of the indole series exist in the open acid form. The anomalies in the spectral behavior in alkaline media are determined by the formation of an anion involving the indole hydrogen atom.     

Tetrahalosubstituted condensed indoles

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1696–1697, December, 1990.     

Nucleophilic reactivities of indoles

The kinetics of the coupling of indole (1a), N-methylindole (1b), 5-methoxyindole (1c), and 5-cyanoindole (1d) with a set of reference benzhydryl cations have been investigated in acetonitrile and/or dichloromethane. The second-order rate constants for the reactions correlate linearly with the electrophilicity parameter E of the benzhydryl cations. This allows the determination of the reactivity parameters, N and s, characterizing the nucleophilicity of 1a-d according to the linear free enthalpy relationship log k(20 degrees C) = s(N + E) (Acc. Chem. Res. 2003, 36, 66). The nucleophilicity parameters thus defined describe nicely the reactions of 1a-d with 4,6-dinitrobenzofuroxan (2), a neutral superelectrophilic heteroaromatic whose electrophilicity (E) has been recently determined. On this ground, the kinetics of the coupling of 2 with a large variety of indole structures have been studied in acetonitrile, leading to a ranking of this family of pi-excessive carbon nucleophiles over a large domain of the nucleophilicity scale N. Importantly, two linear and parallel correlations are obtained on plotting the measured N values versus the pK(a)(H(2)O) values for protonation at C-3 of 5-X-substituted indoles and 5-X-substituted 2-methylindoles, respectively. This splitting reveals that the presence of the 2-methyl group causes steric hindrance to the approach of 2 from the adjacent C-3 position of an indole structure. The N vs pK(a)(H(2)O) correlation for 5-X-substituted indoles is used for a rapid determination of the C-3 basicity of indoles whose acidity constants cannot be measured through equilibrium studies in strongly acidic aqueous media.     

Cascades to substituted indoles

This paper describes the synthesis of dithioindoles from the free-radical cyclizations of arylisonitriles having pendant alkynes. Also described is the synthesis of substituted indoles and spiro-fused indoles from the coupling of dithioindoles with active hydrogen-containing compounds.     

Friedel-Crafts alkylation of indoles

The alkylation of indole and 2-methylindole with alkyl halides in the presence of a complex catalyst — dipyridinezinc chloride — was investigated. Nitromethane was used as the solvent. 3-Alkylindoles were obtained in 30–80% yields in all cases. The reaction mechanism is discussed. Data from the PMR and mass spectra are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 921–924, July, 1978.     

The chemistry of indoles

It has been established that when -oxonitrile arylhydrazones are boiled in glacial acetic acid substituted -carbolines are formed.It has been established that when -oxonitrile arylhydrazones are boiled in glacial acetic acid substituted -carbolines are formed.For part XIV, see [1].     

A trans diacyloxylation of indoles

A trans diacyloxylation of indoles is accomplished by employing PhI(OAc)(2) as the oxidant. A broad range of functional groups are well tolerated. Both the electronic properties of the N-protecting groups of indoles and the acidity of the reaction media play important roles in the selectivity of indole acyloxylation reactions.     

Intramolecular diels-alder reactions of indoles

The first examples of intramolecular Diels-Alder reactions on indoles indicate that this reaction may be employed for the direct preparation of highly functionalized dihydroindoles. The hybridization of the atoms in the tether plays a crucial role.     

Efficient palladium-catalyzed N-arylation of indoles

[equation--see text] The N-arylation of indoles, including a variety of substituted ones, has been carried out using bulky, electron-rich phosphines as the supporting ligand in combination with Pd(2)(dba)(3). Using this catalyst system, the efficient coupling of indole and a variety of substituted indoles with aryl iodides, bromides, chlorides, and triflates can be achieved.     

The copper-catalyzed N-arylation of indoles

A general method for the N-arylation of indoles using catalysts derived from CuI and trans-1,2-cyclohexanediamine (1a), trans-N,N'-dimethyl-1,2-cyclohexanediamine (2a), or N,N'-dimethyl-ethylenediamine (3) is reported. N-Arylindoles can be produced in high yield from the coupling of an aryl iodide or aryl bromide with a variety of indoles.     

Synthesis of noval benzoylated indoles

It has been shown that Friedel-Crafts p-nitrobenzoylation of 2,2-dicarbethoxybis(5-indoyl)methane occurs at the bridging group. From the products of p-nitrobenzoylation of 2-carbethoxy-5-methylindole, 2-carbethoxy-5-hydroxy-indole and 2,7-dicarbethoxy-1H,6H-pyrrolo[2,3-e]indole there were obtained corresponding amines and an oxime.Iv. Dzhavakhishvili State University, Tbilisi 380028. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1202–1205, September, 1994. Original article submitted September 15, 1994.     

Synthesis of 2-substituted indoles

2-Substituted indoles are obtained upon the cyclocondensation of (2-R-2-oxoethyl) trimethylammonium bromides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 509–511, February, 1991.     

Radical cyclisation reactions with indoles

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.     

Reaction of indoles with aldehydes. Synthesis of dihydropyrrolo[3,4-b]indoles

Aromatic aldehydes react with amides of 1-methylindole-2-carboxylic acid under acid catalysis conditions to give 1-aryl-4-methyldihydropyrrolo[3,4-b]indol-3-ones. The intermediate 1-methyl-2-CONHR-3(-X-benzyl)indoles, which are subsequently converted to the indicated cyclic compounds, were isolated. o-Acetyl derivatives were obtained by the action of acetic anhydride on derivatives of unsubstituted amides. Dihydropyrrolo[3,4-b] indol-3-ones were reduced by LiAlH₄ to the corresponding dihydropyrrolo[3,4-b] indoles. A mechanism for the formation of dihydropyrrolo[3,4-b] indoles is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1516–1523, November, 1976.     

Synthesis of indoles via amidoselenation

The reaction of 2-styrylacetanilides (2) with N-phenylselenosuccinimide affords 1-N-acetyl-2-phenyl-3-phenylselenoindoles (3) and 1-N-acetyl-2-phenylindoles (4) . The reaction of 2-vinylacetanilides (5) with phenylselenenyl bromide proceeds to form indoles via an intramolecular amidoselenation.     

New MCR-Heck-isomerization cascade toward indoles

The use of ortho-iodonitrophenol in Ugi-Smiles reaction coupled with Heck cyclization gives new access to indole scaffolds. The sequence can be performed in a one-pot reaction if the residual isocyanide is neutralized prior to the addition of the palladium catalyst.