Direct palladium-catalyzed C-3 arylation of indoles

On the Barton Copper-Catalyzed C3-Arylation of Indoles using Triarylbismuth bis(trifluoroacetate) Reagents

We disclose herein our detailed investigation into the Barton copper-promoted C3-arylation of indoles using triarylbismuth bis(trifluoroacetates). The arylation of unsubstituted 1H-indole using Barton's conditions gave a low yield of the C3-arylated indole, along with small amounts of the product of double C2/C3-arylation and traces of the product of C2 arylation. On the contrary, the arylation of indoles blocked at the C2 position is highly efficient, affording the desired products of C3-arylation in good to excellent yields. The reaction operates under simple conditions, shows good substrate scope, excellent functional group compatibility, and allows the transfer of electron-neutral or deficient aryl groups. Computational studies propose a mechanism involving a trifluoroacetate-assisted C-H activation step.

Palladium-Catalysed Intermolecular Direct C–H Bond Arylation of Heteroarenes with Reagents Alternative to Aryl Halides: Current State of the Art

Abstract:

Abstract: This unprecedented review with 322 references provides a critical up-to-date picture of the Pd-catalysed intermolecular direct C–H bond arylation of heteroarenes with arylating reagents alternative to aryl halides that include aryl sulfonates (aryl triflates, tosylates, mesylates, and imidazole-1-sulfonates), diaryliodonium salts, [(diacetoxy)iodo]arenes, arenediazonium salts, 1-aryltriazenes, arylhydrazines and N’-arylhydrazides, arenesulfonyl chlorides, sodium arenesulfinates, arenesulfinic acids, and arenesulfonohydrazides. Particular attention has been paid to summarise the preparation of the various arylating reagents and to highlight the practicality, versatility, and limitations of the various developed arylation protocols, also comparing their results with those achieved in analogous Pd-catalysed arylation reactions involving the use of aryl halides as electrophiles. Mechanistic proposals have also been briefly summarised and discussed. However, data concerning Pd-catalysed direct C–H bond arylations involving the C–H bonds of aryl substituents of the examined heteroarene derivatives have not been taken into account.

C3-Arylation of indoles with aryl ketones via C-C/C-H activations

C3-Arylation of indoles with aryl ketones is accomplished via palladium-catalyzed ligand-promoted Ar-C(O) cleavage and subsequent C-H arylation of indole. Various (hetero)aryl ketones are compatible in this reaction, affording the corresponding 3-arylindoles in moderate to good yields. Further introduction of an indole moiety into the natural products desoxyestrone and evodiamine demonstrate the synthetic utility of this protocol.

Copper(II)-Catalyzed Direct C-H (Hetero)arylation at the C3 Position of Indoles Assisted by a Removable N,N-Bidentate Auxiliary Moiety

The regioselective arylation of inert C3-H bonds in indoles reacting with arylboronates via effective copper-mediated catalysis with the aid of a facile and removable 2-pyridinylisopropyl (PIP) group without ligand participation is reported. This newly established method features high compatibility with diverse functional groups between coupling partners, including both indole substrates and arylboron reagents, consequentially leading to operational simplicity and providing access to generate the desired arylated products in good to excellent yields of up to 97%. Synthetically, the PIP-derived amide moiety could subsequently be readily removed under mild reaction conditions to produce useful indole carboxylic acids for further transformation.

Pd/β-cyclodextrin-catalyzed C–H functionalization in water: a greener approach to regioselective arylation of (NH)-indoles with aryl bromides

A greener and more practical approach to the regioselective C3/C2-arylation of (NH)-indoles with (hetero)aryl bromides in water is developed via the Na2PdCl4-catalyzed and β-cyclodextrin ligand-mediated cross-coupling reactions.

Transition metal-catalyzed C–H functionalizations of indoles

This review summarises a wide range of transformations on the indole skeleton, including arylation, alkenylation, alkynylation, acylation, nitration, borylation, and amidation, using transition-metal catalyzed C–H functionalization as the key step.

Palladium-Catalyzed Cross-Coupling Reactions of 4-Tosyl­oxyquinazolines with Indoles: An Efficient Approach to 4-(1H-Indol-1-yl)quinazolines

In this paper, exploration of our continuous interests on late-stage derivation of quinozaline core is described. A wide array of 4-(1H-indol-1-yl)quinazolines were obtained in good to excellent yields through palladium-catalyzed cross-coupling of 4-tosyloxyquinazolines with indole derivatives under mild reaction conditions.

Direct C3-Selective Arylation of N-Unsubstituted Indoles with Aryl Chlorides, Triflates, and Nonaflates Using a Palladium-Dihydroxyterphenylphosphine Catalyst

A palladium-dihydroxyterphenylphosphine (DHTP) catalyst was successfully applied to the direct C3-arylation of N-unsubstituted indoles with aryl chlorides, triflates, and nonaflates. This catalyst showed C3-selectivity, whereas catalysts with other structurally related ligands exhibited N1-selectivity. Complex formation between the lithium salts of the ligand and the indole is assumed to accelerate the arylation at the C3 position. Reactions using 3-alkylindoles afforded 3,3-disubstituted indolenines, which can be further converted to the corresponding indoline derivatives.

Regioselective Pd-catalyzed direct C1- and C2-arylations of lilolidine for the access to 5,6-dihydropyrrolo[3,2,1-ij]quinoline derivatives

The Pd-catalyzed C–H bond functionalization of lilolidine was investigated. The use of a palladium-diphosphine catalyst associated to acetate bases in DMA was found to promote the regioselective arylation at α-position of the nitrogen atom of lilolidine with a wide variety of aryl bromides. From these α-arylated lilolidines, a second arylation at the β-position gives the access to α,β-diarylated lilolidines containing two different aryl groups. The one pot access to α,β-diarylated lilolidines with two identical aryl groups is also possible by using a larger amount of aryl bromide. The synthesis of 5,6-dihydrodibenzo[a,c]pyrido[3,2,1-jk]carbazoles from lilolidine via three successive direct arylations is also described. Therefore, this methodology provides a straightforward access to several lilolidine derivatives from commercially available compounds via one, two or three C–H bond functionalization steps allowing to tune their biological properties.

Coordination chemistry and catalysis with secondary phosphine oxides

Review on synthesis, coordination chemistry and catalysis with secondary phosphine oxides.

A general synthesis of arylindoles and (1-arylvinyl)carbazoles via a one-pot reaction from N-tosylhydrazones and 2-nitro-haloarenes and their potential application to colon cancer

A convergent and effective synthesis of 3-aryl-indoles, 2,3-diaryl indoles, and (1-arylvinyl)carbazoles from a one-pot sequence involving the coupling of N-tosylhydrazones with ortho-nitro-haloarenes followed by a cyclization has been developed. Compound 5i exhibits excellent antiproliferative activity in the low nM range against colon cancer cell lines.

Regioselective direct arylation of indoles on the benzenoid moiety

Recent advances in transition metal-catalyzed selective C–H functionalization of indoles have garnered tremendous attention.

Transition metal-catalyzed site- and regio-divergent C–H bond functionalization

The regioselectivity of C–H functionalization reactions can be redirected to obtain regioisomeric products form the same starting materials.

Synthesis of 3-arylindole derivatives from nitroalkane precursors

3-Arylindole derivatives were synthesized by Cu(i) catalysed intramolecular Ullmann coupling of 2-bromoarylaminoalkanes.

Regioselectivity in palladium-catalysed direct arylation of 5-membered ring heteroaromatics

In the past few years, several results using modified catalysts and new reaction conditions have been reported permitting better control of the regioselectivity of Pd-catalysed arylations.

Friedel–Crafts reaction of indoles with vicinal tricarbonyl compounds generated in situ from 1,3-dicarbonyl compounds and TEMPO: highly selective synthesis of tertiary alcohols

A novel Friedel–Crafts reaction of indoles with vicinal tricarbonyl compounds generated in situ has been developed, forming indolyl tertiary alcohols. The process involves disproportionation of TEMPO, α-oxyamination, N–O bond cleavage and, finally, addition of the indole.

Palladium nanoparticles supported on modified single-walled carbon nanotubes: a heterogeneous and reusable catalyst in the Ullmann-type N-arylation of imidazoles and indoles

Application of SWCNT-Met/Pd as an efficient and heterogeneous catalyst in the Ullmann coupling of imidazoles and indoles with aryl iodides.

Advances in direct C–H arylation of 5,5- 6,5- and 6,6-fused-heterocycles containing heteroatoms (N, O, S)

This report aims to review the advances made in C–H arylation of 5,6, 6,6 and 5,5 fused-heterocyclic systems.

KO(t)Bu-mediated aerobic transition-metal-free regioselective β-arylation of indoles: synthesis of β-(2-/4-nitroaryl)-indoles

A KO(t)Bu-mediated intermolecular oxidative C-C coupling of nitroarenes with indoles is presented in DMSO at room temperature in an open flask. By using this mild and economical methodology, syntheses of β-(2/4-nitroaryl)-indoles with sensitive functionalities such as bromo, iodo, cyano, and nitro were achieved chemo- and regioselectively. Synthesized β-(2/4-nitroaryl) indoles were transformed into densely functionalized biindoles, indoloindoles, and (4-aminoaryl)-indoles which demonstrate post-transformation utility of the developed methodology.

Exploration of C-H and N-H-bond functionalization towards 1-(1,2-diarylindol-3-yl)tetrahydroisoquinolines

The synthesis of 1,2,3-trisubstituted indoles was investigated. More specifically, straightforward synthetic routes towards 1-(1,2-diarylindol-3-yl)-N-PG-THIQs (PG = protecting group, THIQ = tetrahydroisoquinoline) employing transition metal-catalyzed C-H and N-H-bond functionalization were explored. It was found that the synthesis of the target compounds is strongly dependent on the order of events. Hence, depending on the requirements of a synthetic problem the most suitable and promising pathway can be chosen. Additionally, a new synthetic approach towards 1,2-diarylindoles starting from 1-arylindole could be established in the course of our investigation by using a palladium-catalyzed protocol. Such 1,2-diarylindoles were successfully reacted with N-Boc-THIQ to furnish 1,2,3-trisubstituted indoles as target compounds. Furthermore, regioselective N-arylation of protected and unprotected 1-(indol-3-yl)-THIQs was successfully conducted using either simple iron or copper salts as catalysts.

A highly efficient and recyclable Fe3O4 magnetic nanoparticle immobilized palladium catalyst for the direct C-2 arylation of indoles with arylboronic acids

An efficient and reusable Fe₃O₄-nanoparticle-immobilized-palladium catalyst was prepared and applied to the direct C-2 arylation of indoles with arylboronic acids.

Methyl 4-(5-methoxy-1H-indol-3-yl)benzoate

In the title compound, C₁₇H₁₅NO₃, the dihedral angle between the benzene ring and the indole ring system is 22.5 (3)°. In the crystal, mol­ecules are linked by N—H⋯π and C—H⋯O inter­actions.