Access to Indole Derivatives from Diaryliodonium Salts and 2-Alkynylanilines

Camphorsulfonic Acid-Mediated One-Pot Tandem Consecutive via the Ugi Four-Component Reaction for the Synthesis of Functionalized Indole and 2-Quinolone Derivatives by Switching Solvents

A camphorsulfonic acid-mediated one-pot tandem consecutive approach was developed to synthesize functionalized indole and 2-quinolone derivatives from the Ugi four-component reaction by switching solvents. A reaction of the Ugi adduct in an aprotic solvent undergoes 5-exo-trig cyclization to form an indole ring. In a protic solvent, however, the Ugi adduct undergoes an alkyne-carbonyl metathesis reaction to form a 2-quinolone ring.

An approach to unsymmetrical 3,3′-diindolylmethanes through Pd-catalyzed cascade Heck cyclization of allenamides and o-ethynylanilines

A highly efficient synthesis of unsymmetrical 3,3′-diindolylmethanes has been developed by palladium-catalyzed cascade Heck/cyclization reaction.

Hypervalent iodine mediated synthesis of imidazo[1,2-a]pyridine ethers: consecutive methylene linkage and insertion of ethylene glycol

Hypervalent iodine mediated selective synthesis of imidazo[1,2-a]pyridine ethers using ethylene glycol as a methoxy ethanol source as well as solvent under metal-free conditions is described.

Synthesis of indoles from alkynes and a nitrogen source under metal-free conditions

This review deals with the methodologies published in the last ten years, which used metal-free conditions to prepare indoles starting from alkynes and nitrogen compounds.

On water: iodine-mediated direct construction of 1,3-benzothiazines from ortho-alkynylanilines by regioselective 6-exo-dig cyclization

Herein, we report the 6-exo-dig ring closure of ortho-alkynylanilines with readily available aroyl isothiocyanate. An environmentally benign, metal- and base-free, iodine promoted cascade synthesis of highly functionalized (benzo[1,3]thiazin-2-yl)benzimidic acids has been accomplished via in situ generated ortho-alkynylthiourea. The established methodology employs the abundant chemical feedstock of ortho-alkynylanilines and aroyl isothiocyanates and could be applied in the late-stage synthesis of pharmaceutically active 1,3-benzothiazine containing molecules. Furthermore, the discovered protocol exclusively delivers bis (benzo[1,3]thiazin-2-yl)dibenzimidic acid products and preserves the iodo-olefin substitution pattern which can be exploited by further derivatization.

Regioselective three-component synthesis of 1,2-diarylindoles from cyclohexanones, α-hydroxyketones and anilines under transition-metal-free conditions

A facile method for the one-pot synthesis of 1,2-diarylindoles under transition-metal-free conditions is described.

Copper-Catalyzed Synthesis of Substituted Quinazolines from Benzonitriles and 2-Ethynylanilines via Carbon-Carbon Bond Cleavage Using Molecular Oxygen

A copper-catalyzed process for the synthesis of substituted quinazolines from benzonitriles and 2-ethynylanilines using molecular oxygen (O₂) as sole oxidant is described. The mild catalytic system enabled the effective cleavage of the C-C triple bond and construction of new C-N and C-C bonds in one operation. Furthermore, the compound N, N-dimethyl-4-(2-(4-(trifluoromethyl)phenyl)quinazolin-4-yl)aniline (3dj) exhibited obvious aggregation-induced emission phenomenon, and the fluorescence quantum yield (Φ_F,film) and lifetime (τ_film) were measured to be 45.5% and 5.8 ns in thin films state, respectively.

Acid-promoted oxidative methylenation of 1,3-dicarbonyl compounds with DMSO: application to the three-component synthesis of Hantzsch-type pyridines

A series of polysubstituted pyridines and methylene-bridged bis-1,3-dicarbonyl compounds were prepared in high yields from 1,3-dicarbonyl compounds and DMSO, wherein DMSO serves as solvent, carbon source, and oxidant.

Selective C–N coupling reaction of diaryliodonium salts and dinucleophiles

Ligand-free copper-catalyzed selective N-arylation of dinucleophiles including chiral α-amino amides with diaryliodonium salts as aryl electrophile equivalents was realized. Diaryliodonium salts prefer to react with dinucleophiles at the site of stronger basic amino groups.

Metal-free Synthesis of Aryl Amines: Beyond Nucleophilic Aromatic Substitution

A mild and metal-free approach to C-N coupling is described that employs diaryliodonium salt electrophiles and secondary aliphatic amine nucleophiles. This reaction results in direct ipso-substitution of the iodonium moiety and unsymmetrical aryl(TMP)iodonium salts are primarily employed. Moreover, arene substituents and substitution patterns that currently pose a challenge to classical metal-free methods are accommodated and the alicyclic amine nucleophiles used here are unprecedented in other contemporary metal-free C-N coupling reactions.

Direct synthesis of nitroaryl acetylenes from acetylenes and nitroarenes via oxidative nucleophilic substitution of hydrogen

Acetylenic carbanions add to nitroarenes (dinitrobenzenes, nitropyridines, etc.) to form σ^H-adducts that are subsequently oxidized by DDQ according to the oxidative nucleophilic substitution of hydrogen (ONSH) pathway to give nitroaryl acetylenes.

H2O2/DMSO-Promoted Regioselective Synthesis of 3,3'-Bisimidazopyridinylmethanes via Intermolecular Oxidative C(sp(2))-H Bond Activation of Imidazoheterocycles

In the past decade, metal-free approaches for C-C bond formation have attracted a great deal of attention due to their ease of use and low cost. This report represents a novel and metal-free synthesis of 3,3'-bisimidazopyridinylmethanes via intermolecular oxidative C(sp(2))-H bond functionalization of imidazo[1,2-a]pyridines with dimethyl sulfoxide as the carbon synthon (CH2) using H2O2 as a mild oxidant under air. A library of 3,3'-bis(2-arylimidazo[1,2-a]pyridin-3-yl)methanes has been achieved in good to excellent yields. The present methodology has been successfully applied to imidazo[2,1-b]thiazoles and imidazo[2,1-b]benzothiazoles. Furthermore, the current approach was also extended for the synthesis of unsymmetrical 3,3'-bisimidazopyridinylmethanes under optimized reaction conditions. A mechanistic pathway is proposed on the basis of experiments with radical scavengers and DMSO-d6 and ESI-MS observations.