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.     

2-取代吲哚的染料敏化光氧化反应

2-苯基吲哚 (1a) 在甲醇中的染料敏化光氧化反应给出2-苯基-2-(2'-苯基-3'-吲哚基)二氢吲哚-3-酮 (2a) 和2-甲氧基-2-苯基二氢吲哚-3-酮 (4a), 相应N-甲基取代产物由1-甲基-2-苯基吲哚 (1b) 的类似反应获得。发现反应产物分布随吲哚 (1) 的浓度和介质酸度的变化而变化。对反应机理进行了推测, 其中当1a的反应在乙腈中进行时, 分离到了相应的反应中间体: 2-苯基-3H-吲哚-3-酮 (3a)。     

Cyclization of alpha-Oxo-oximes to 2-substituted benzoxazoles

Reactions of oximes 9, 17, and 19 with electrophiles 15a-f and 24 in the presence of anhydrous potassium carbonate or triethylamine give 2-substituted condensed ring oxazoles 10, 16a-c, 18a-d, 20a-c, and 25 in a new general route to these compounds.     

Synthesis of 2-substituted indoles by palladium-catalyzed heteroannulation with Pd-NaY zeolite catalysts

Various 2-substituted indoles were prepared by heteroannulation of o-iodoanilines and terminal alkynes in a one-pot reaction with a Pd(II)-NaY zeolite catalyst. The product formation largely depended on the solvent, base, and reaction temperature. The recycled catalyst showed good reusability in the heteroannulation reaction.     

A highly selective Ir-catalyzed borylation of 2-substituted indoles: a new access to 2,7- and 2,4,7-substituted indoles

The selective CH-functionalization of 2-substituted indoles is presented. Using bis(pinacolato)diboron (2) in the presence of iridium complexes, a novel catalytic mono-borylation is observed preferentially at the 7-position of the indole. This allows for an efficient synthesis of various 2,7-di- and 2,4,7-trisubstituted indoles, which are otherwise difficult to access. The scope and limitation of the method is demonstrated.     

6-substituted indoles from o-halonitrobenzenes

o-Chloro- and o-bromonitrobenzenes are efficiently converted to 6-substituted indoles in a four step synthesis, proceeding through o-trimethylsilylethynylnitrobenzenes, o-nitrophenylacetaldehyde dimethylacetals and o-aminophenylacetaldehyde dimethylacetals as intermediates.o-Chloro- and o-bromonitrobenzenes are efficiently converted to 6-substituted indoles in a four step synthesis. R = CO₂Me(H), COPh, Ph, CF₃ and Me.     

Syntheses of 2-substituted indoles and fused indoles by photostimulated reactions of o-iodoanilines with carbanions by the SRN1 mechanism

2-Substituted indoles (5a,b and 7) and fused indoles (9a-c, 11a,b, and 12) have been obtained by the S(RN)1 mechanism from photostimulated reactions of o-iodoaniline (1) and 1-halo-2-naphthalen-2-ylamines (3a,b) with enolate ions of acyclic (acetophenone (6), 2- (4a) and 4-acetylpyridine (4b)) and cyclic ketones (1- (8a) and 2-indanone (10a), 1- (8b) and 2-tetralone (10b) and 1-benzosuberone (8c)) in DMSO and liquid ammonia as solvents. The carbanions derived from 4a,b, 8a, and 10b are novel nucleophiles that form new C-C bonds by the S(RN)1 mechanism.     

Hydroxyalkylation of 4,5,6,7-tetrahydroindole with polyfluorocarbonyl compounds as a route to 2-substituted indoles

The regioselective hydroxyalkylation of 4,5,6,7-tetrahydroindole at position 2 using highly electrophilic polyfluorocarbonyl compounds was performed for the first time. Oxidation of the products thus formed leads to indoles having 2-hydroxypolyfluoroalkyl and polyfluoroacyl groups.     

A facile synthesis of 3-substituted indoles

1-Benzoyl-3-bromomethylindole (2a) or 1-benzenesulfonyl-3-bromomethylindole (2b) reacts with C, N, O, and P-containing nucleophiles to give potential intermediates for the synthesis of a wide range of indole alkaloids and pharmacologically important substances, in good to excellent yields.     

Benzannulation of 3-substituted pyrroles to indoles

In a new general indole synthesis, the anion derived from benzotriazolyl derivative 5b underwent regioselective 1,4-addition to various alpha,beta-unsaturated ketones; subsequent acid-catalyzed cyclization formed the corresponding indoles 1a-f.     

Solid-state synthesis of novel 3-substituted indoles

Poly(N-bromo-N-ethyl-benzene-1,3-disulfonamide) [PBBS] and N,N,N’,N’-tetrabromobenzene-1,3-disulfonamide [TBBDA] were used as efficient catalysts for the one-pot synthesis of 3-substituted indoles in good to high yields from indole, aldehydes, and arylamines under solid-state conditions at room temperature.     

Alkylation of 5-substituted tetrazoles with mannich bases

Mixtures of N(₁) and N(₂) isomers are formed in the alkylation of 1H-5-R-tetrazoles with N-(2-hydroxy-3-methoxy-5-formylbenzyl)piperidine, whereas primarily one of two possible N(₁) or N(₂) isomers is formed in the case of alkylation with N-(3,5-di-methyl-4-hydroxybenzyl)piperidine, depending on substituent R.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 851–853, June, 1984.     

A convenient synthesis of pyrrolopyridines and 2-substituted indoles by gold-catalyzed cycloisomerization

We have developed a gold-catalyzed intramolecular cyclization of variously substituted acetylenic amines under mild conditions, which yields pyrrolopyridines and 2-substituted indoles, quantitatively. The cycloisomerization of acetylenic amines was achieved with AuCl₃ as catalyst without the use of base, acid or N-protecting group.     

Novel synthesis of fused indoles and 2-substituted indoles by the palladium-catalyzed cyclization of N-cycloalkenyl-o-haloanilines

A new palladium-catalyzed cyclization of N-alkenyl-o-haloanilines with selective isomerization of a double bond followed by formal 5-endo-trig cyclization was developed. A variety of fused and 2-substituted indoles were synthesized from enaminoesters prepared by condensation of β-ketoesters and o-iodoaniline.     

Synthesis of 3-substituted indoles via N-acylindolium ions

3-Substituted N-(N′N′-diethylcarbamyl)indoles are prepared from indole-3-carboxaldehyde in good overall yield via N-acylindolium ion intermediates.     

Ruthenium-catalyzed regioselective synthesis of 2-substituted indoles via ring-opening of epoxides by anilines

Anilines react with epoxides in dioxane at 180°C in the presence of a catalytic amount of a ruthenium catalyst along with tin(II) chloride to afford 2-substituted indoles in moderate to good yields.     

Synthesis of 2-substituted indoles via a palladium-catalyzed domino Heck reaction and dealkylation

A palladium-catalyzed domino Heck reaction and dealkylation for the preparation of 2-substituted indoles is described. This novel transformation is based on an intramolecular Heck reaction followed by dealkylation.     

ZnCl2 and Pd/C catalyzed synthesis of 2-substituted indoles

A facile, mild, efficient, and copper-free method has been developed for the synthesis of 2-substituted indoles via domino Sonogashira coupling/cyclization reaction catalyzed by ZnCl₂ and palladium on carbon with simultaneous formations of C–C and C–N bonds.