Indoles In High Yields Research Articles

Facile synthesis of indoles by K2CO3 catalyzed cyclization reaction of 2-ethynylanilines in water

The cyclization reaction of 2-ethynyl-N-sulfonylanilides proceeded efficiently in water with the presence of a catalytic amount of K2CO3 under transition metal-free condition to give indoles in high yields. The recovery and reusability of the present catalytic system were investigated.

ChemInform Abstract: Stereocontrolled Construction of the Dihydrothiopyrano[2,3‐b]indole Skeleton via an Organocatalyzed Asymmetric Cascade Sulfa‐Michael‐Aldol Reaction.

Abstract We have developed an organocatalyzed asymmetric cascade sulfa-Michael-aldol reaction between 2-mercaptoindole-3-carbaldehydes and enals, which provides efficient access to the stereocontrolled construction of dihydrothiopyrano[2,3- b ]indole skeletons. Under the catalysis of chiral diphenylprolinol TMS ether, the reactions ran smoothly to give the corresponding synthetically useful and pharmaceutically valuable dihydrothiopyrano[2,3- b ]indoles in high yields and with 64–96% ee.

Stereocontrolled construction of the dihydrothiopyrano[2,3-b]indole skeleton via an organocatalyzed asymmetric cascade sulfa-Michael-aldol reaction

We have developed an organocatalyzed asymmetric cascade sulfa-Michael-aldol reaction between 2-mercaptoindole-3-carbaldehydes and enals, which provides efficient access to the stereocontrolled construction of dihydrothiopyrano[2,3-b]indole skeletons. Under the catalysis of chiral diphenylprolinol TMS ether, the reactions ran smoothly to give the corresponding synthetically useful and pharmaceutically valuable dihydrothiopyrano[2,3-b]indoles in high yields and with 64–96% ee.

Rhodium‐Catalyzed Decarbonylative Direct C2‐Arylation of Indoles with Aryl Carboxylic Acids

AbstractA RhI‐catalyzed direct C2‐arylation of indoles with diversely substituted aryl carboxylic acids has been developed using 2‐pyrimidyl group as an easily installable and readily removable N‐directing group. The reaction proceeded smoothly without the need for any external oxidants under relatively mild conditions to produce the C2‐arylated indoles in high yields with excellent regioselectivity. A range of functional groups in both coupling partners were tolerated regardless of their electronic properties and positions. With the assistance of the 2‐pyrimidyl group, these C2‐functionalized products could further undergo C7‐arylation to give the C7‐aryl indole products. Mechanistic evidence supports that the reaction involves a decarbonylation step, and the carboxylic acids could be activated in situ by treatment with (tBuCO)2O to generate the active anhydrides.

Indole Synthesis Based On A Modified Koser Reagent

A new metal-free method for the rapid and productive preparation of indoles has been developed. This process is based on sterically congested hypervalent iodine compounds of the family of Koser reagents, and iodosobenzene in combination with 2,4,5-tris-isopropylbenzene sulfonic acid provides the highest yields and fastest reaction times. This reagent alone promotes the chemoselective oxidative cyclization of 2-amino styrenes to indoles in high yields under mild conditions.

Transition‐Metal‐Catalyzed Regioselective Alkylation of Indoles with Alcohols

AbstractThe regioselective alkylation of indoles with alcohols as alkylating reagents was developed by using Pd/C or RuCl2(PPh3)3/DPEphos {DPEphos = bis[(2‐diphenylphosphanyl)phenyl] ether}as catalysts. The reaction of indole with benzyl alcohol in the presence of Pd/C and K2CO3 at 80 °C for 24 h without any solvent under in air yielded 90 % of 3‐benzylindole. The corresponding 3‐benzylindole was obtained in 99 % yield when the reaction was catalyzed by RuCl2(PPh3)3/DPEphos in the presence of K3PO4 at 165 °C for 24 h under argon. Several types of alcohols were treated with indoles under these conditions to give the corresponding 3‐alkylated indoles in high yields (up to 99 %). This reaction may involve the catalyst‐mediated transformation of alcohols to aldehydes, nucleophilic addition of indole to the resulting aldehydes accompanied by dehydration, and then hydrogenation.

Indoles Synthesized from Amines via Copper Catalysis

N-substituted indoles are synthesized from primary amines through a tandem reaction sequence. Initial condensation of the amine with an α-(o-haloaryl)ketone or aldehyde is followed by intramolecular aryl amination catalyzed by CuI. A variety of anilines and alkyl amines, including those with significant steric demands, are converted to indoles in high yields and with varying indole substitution.

ChemInform Abstract: Rhodium Acetate/Base‐Catalyzed N‐Silylation of Indole Derivatives with Hydrosilanes.

In the presence of Rh(2)(OAc)(4) (OAc = acetate) and TBA(2)WO(4) (TBA = tetra-n-butylammonium), the N-silylation of indole derivatives with hydrosilanes efficiently proceeded to give the corresponding N-silylated indoles in high yields. Pyrrole and carbazole were also N-silylated with the combined catalysts.

Cyclopentadiene–Phosphine/Palladium-Catalyzed Cleavage of C–N Bonds in Secondary Amines: Synthesis of Pyrrole and Indole Derivatives from Secondary Amines and Alkenyl or Aryl Dibromides

An efficient Pd-catalyzed cleavage of C(sp(3))-N bonds in secondary amines and a consequent C(sp(2))-N and C(sp(3))-N coupling process was developed. Various secondary amines could be used to react with alkenyl or aryl dibromides, affording pyrroles and indoles in high yields. Cyclopentadiene-phosphine ligands, a new type of P-olefin ligand, were found to be able to promote the efficiency of this Pd-catalyzed process remarkably. A reactive Pd complex coordinated with a cyclopentadiene-phosphine ligand was successfully isolated and structurally characterized.

Facile Access to Polysubstituted Indoles via Three Component One - Pot Reactions

A simple and efficient method for the synthesis of a novel series of 2, 3, 5 trisubstituted indoles in high yields is discribed from an one-pot, three-component reaction of p-aniline, the phenylglyoxals and barbituric acid or dimedon in HOAc.

Rhodium acetate/base-catalyzed N-silylation of indole derivatives with hydrosilanes

In the presence of Rh(2)(OAc)(4) (OAc = acetate) and TBA(2)WO(4) (TBA = tetra-n-butylammonium), the N-silylation of indole derivatives with hydrosilanes efficiently proceeded to give the corresponding N-silylated indoles in high yields. Pyrrole and carbazole were also N-silylated with the combined catalysts.

Synthesis of Polysubstituted Indoles via Three-Component Reaction

A copper-catalyzed three-component reaction of 2-ethynylanilines, tosyl azide, and nitroolefins is reported. It proceeds under mild conditions and generates functionalized indoles in high yields.

2-Vinylindoles As the Four-Atom Component in a Catalytic [4+1] Cycloaddition with a Silylene-Palladium Species Generated from (Aminosilyl)boronic Ester

The palladium-catalyzed silylene transfer to 2-alkenylindoles from a silylboronic ester bearing a diethylamino group on the silicon atom takes place efficiently, resulting in the formation of a 1-sila-3-cyclopentene ring fused with the indole ring. Further silylene transfer proceeds in the reaction of 2-(1-alkenyl)indoles, giving bissilylated tricyclic indoles in high yields.

Highly Efficient InBr3 Catalyzed Michael Addition of Indoles to α,β‐Unsaturated Esters

AbstractA highly efficient synthetic strategy toward Michael addition of indoles to α,β‐unsaturated esters has been developed using Lewis acid InBr3 as catalyst. The reactions generated 3‐substituted indoles in high yields with excellent regio‐selectivity in the presence of catalytic amount of InBr3 under mild reaction conditions. The method is simple, efficient and practical.

Friedel−Crafts Acylation of Pyrroles and Indoles using 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) as a Nucleophilic Catalyst

1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) has been shown to be an effective catalyst for the regioselective Friedel-Crafts C-acylation of pyrroles and indoles in high yields. A detailed mechanistic study implies that DBN is acting as a nucleophilic organocatalyst, with the X-ray crystal structure of a key N-acyl-amidine intermediate having been determined for the first time.

Iridium-Catalyzed Heteroannulation Route to Benzofurans and Indoles

Previous studies on the rhodium- and iridium-catalyzed C-H activation of aryl ­ketones form the basis of the reported directed cyclodehydration route of α-aryloxy and α-aryl­amino ketones to benzofuran derivatives. After screening conditions, rhodium was found to be ineffective, but the [Ir(cod)2]BARF complex afforded the corresponding 4-substituted benzofurans and indoles in high yields. Esters, amides, and the acetyl group were found to be applicable as directing group (DG) in the reaction, albeit only one example is provided for esters and amides. The regioselectivity is presumably driven by iridium coordination of DG and the incipient carbonyl involved in the cyclodehydration step. Interestingly, chiral BINAP was successfully applied in the reaction to afford a chiral oxindole with moderate enantioselectivity.

Iridium‐Catalyzed Selective Synthesis of 4‐Substituted Benzofurans and Indoles via Directed Cyclodehydration

AbstractA directed cyclization‐dehydration cascade of α‐aryloxy ketones and α‐arylamino ketones was efficiently catalyzed by a cationic iridium‐BINAP complex, which afforded various types of 4‐substituted benzofurans and indoles in high yields with complete regioselectivity. The newly developed protocol also enabled the enantioselective preparation of chiral 4‐acetyloxindole using a chiral iridium catalyst.

A Flexible Synthesis of 2,3-Disubstituted Indoles from Aminobenzyl Phosphonium Salts. A Direct Synthesis of Rutaecarpine

The reaction of substituted (2-aminobenzyl)triphenylphosphonium bromides with aromatic aldehydes or alpha,beta-unsaturated aldehydes constitutes a new synthesis of 2,3-disubstitued indoles in high yields. The adduct from 4-oxo-3,4-dihydroquinazoline-2-carbaldehyde was an advanced intermediate in the synthesis of several rutaecarpines.

Palladium-free zinc-mediated hydroamination of alkynes: efficient synthesis of indoles from 2-akynylaniline derivatives

Reaction of 2-phenylethynyl N-tosylanilide prepared by Pd-free procedure with ZnBr 2 (3 equiv) in refluxing toluene gave N-tosyl-2-phenylindole in 93% yield. Treatment of 2-phenylethynylaniline with ZnBr 2 (1 equiv) in refluxing toluene resulted in the formation of 2-phenylindole in 91% yield. Catalytic ZnBr 2 (0.05 equiv) effectively reacted with 2-alkynylanilines to afford 2-substituted indoles in high yields. Thus, complete Pd-free zinc catalyzed hydroamination of 2-alkynylanilines was achieved.

One-Pot Synthesis of 2-Substituted Indoles from 2-Aminobenzyl Phosphonium Salts. A Formal Total Synthesis of Arcyriacyanin A

The reaction of (2-aminobenzyl) triphenylphosphonium bromide with aromatic aldehydes or alpha,beta-unsaturated aldehydes under microwave-assisted conditions constitutes a new synthesis of 2-substituted indoles in high yields (81-97%) in a one-pot reaction. The adduct from indole-4-carboxaldehyde was an advanced intermediate in the synthesis of arcyriacyanin A.