[Cp*IrCl2]2 Catalyzed Formation of 2,2′-Biindoles from 2-Ethynylanilines

Efficient approach to 1,1'-bisindoles via copper(I)-catalyzed double domino reaction

A highly efficient copper(I)-catalyzed approach for the synthesis of 1,1'-bisindoles that is based on the formation of four bonds in one step has been developed. The unprecedented three component reaction between one molecule of a 1,2-bis(2-bromoaryl)hydrazine and two molecules of a 1,3-diketone employing 10 mol% CuI as a catalyst and Cs2CO3 as a base in DMSO at 100 °C for 24 h delivers substituted 1,1'-bisindoles with yields up to 92%. The new method proceeds as a double domino condensation/Ullmann type C-C coupling. It allows an efficient and practical access to substituted 1,1'-bisindoles in one step from easily available starting materials.

One-Pot Synthesis of 1,2-Disubstituted Indoles from 2-Ethynylanilines and Benzaldehydes

An efficient synthesis of a variety of 1,2-disubstituted indoles from 2-ethynylanilines was developed. Using 2-ethynylanilines and benzaldehydes as starting materials, the target products (1,2-disubstituted indoles) were obtained smoothly through condensation, reduction, and subsequent cyclization. Various functional groups attached to the aryl ring of 1,2-disubstituted indoles were well tolerated. The protocol features easy performance, easily available starting materials, good yield, and a broad substrate scope, showing potential synthetic value for the preparation of a variety of biologically or pharmaceutically active compounds.

Nickel-Catalyzed trans-Carboamination across Internal Alkynes to Access Multifunctionalized Indoles

A Ni-catalyzed reaction was developed for the synthesis of multifunctionalized indoles. The reaction proceeded through oxidative cyclization of the Ni(0)/P^N complex with an enyne system, 2-alkynyl anilinoacrylate, to provide a nickelacycle intermediate. The trans-carboamination around the internal alkyne was achieved by syn/anti-rotation of the Ni-carbenoid intermediate formed by C-N bond cleavage of the nickelacycle, and 3-alkenylated indoles were formed by C-N bond-forming reductive elimination. Notably, the synthesized indoles could be successfully transformed to functionalized carbazoles.

Rh-Catalyzed nitrene alkyne metathesis/formal C–N bond insertion cascade: synthesis of 3-iminoindolines

A Rh-catalyzed nitrene/alkyne metathesis (NAM) cascade reaction terminated by a formal C–N bond insertion has been developed, which provides facile access to the tricyclic 3-iminoindolines in good yields with broad substrate scope.

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

This review highlights ten years of success in the synthesis of indoles using alkynes and nitrogen sources as substrates.

Metal-Free Oxidative Cross Coupling of Indoles with Electron-Rich (Hetero)arenes

A new method for the synthesis of bi-heteroaryls is reported, based on the umpolung of indoles with benziodoxol(on)e hypervalent iodine reagents (IndoleBX). The oxidative coupling of IndoleBX with an equimolar amount of electron-rich benzenes, indoles, pyrroles, and thiophenes proceeded under mild transition-metal-free conditions. Functionalized non-symmetrical bi-indolyl heterocycles were accessed efficiently. Introduction of a new type of C2-substituted indole benziodoxole reagents further allowed extending the scope of the reaction to NH unprotected and C3-alkylated indoles. The obtained bi-heterocycles are important building blocks in synthetic and medicinal chemistry, and could be easily transformed into more complex heterocyclic systems.

Computational study of Ru-catalyzed cycloisomerization of 2-alkynylanilides

The reaction mechanism of Ru-catalyzed cycloisomerization of 2-alkynylanilides to 3-substituted indole or 2-substituted indole was analyzed at the B3LYP level of density functional theory. The solvation effect of the system was also considered by SMD model. The calculation results show that the reaction system first forms a ruthenium π-alkyne complex. On the one hand, the cyclization reaction of the amino group and the alkyne carbon in the reaction precursor complex directly forms the 2-substituted indole product. On the other hand, the benzene ring in the reaction complex undergoes 1,2-carbon migration on the C≡C triple bond to form the vinylidene complex. After cyclization and hydrogen transfer, the catalyst is regenerated to obtain 3-substituted indole product. The latter reaction process has relatively lower activation free energy and is also the main reaction channel for this reaction, which is consistent with published experimental results. This study provides a reasonable reaction mechanism and effective experimental supplement.

Ruthenium-Catalyzed Cycloisomerization of 2-Alkynylanilides: Synthesis of 3-Substituted Indoles by 1,2-Carbon Migration

We developed ruthenium-catalyzed cycloisomerization of alkynylanilides that gave 3-substituted indoles in high yields. The reaction proceeded via the disubstituted vinylidene ruthenium complex that was formed by the 1,2-carbon migration.

Titanium complexes supported by imidazo[1,5-a]pyridine-containing pyrrolyl ligand as catalysts for hydroamination and polymerization reactions, and as an antitumor reagent

The syntheses, structures, catalytic properties and antitumor activities of three titanium complexes supported by an imidazo[1,5-a]pyridine-containing pyrrolyl ligand are reported.

Flexible and practical synthesis of 3-oxyindoles through gold-catalyzed intermolecular oxidation of o-ethynylanilines

A novel gold-catalyzed intermolecular oxidation of o-ethynylanilines has been developed, which provides a reliable access to synthetically useful 3-oxyindoles. Importantly, this gold-catalyzed oxidative process outcompetes the typical indole formation.