Ligandless Copper-Catalyzed Coupling of Heteroaryl Bromides with Gaseous Ammonia

Halogen bonding accelerated aerobic dehydrogenative aromatization for 4-aminoquinoline preparation

This study presents a highly efficient method for 4-aminoquinoline derivative preparation under transition metal-free conditions. The process involves an aerobic oxidative dehydrative coupling of 2,3-dihydroquinolin-4(1H)-ones with various amines, including ammonia, resulting in high yields of the desired products. The method is also applicable to substituted 4-aminoquinoline derivative construction through a cyclization/dehydrative coupling cascade process starting from 2'-amino chalcones. Mechanistic studies reveal that iodine (I2) is consumed to produce 3-iodoquinolin-4-ol, which acts as a true catalyst with high catalytic efficacy (as low as 0.5 mol%). The presence of halogen bonding is critical in the inter-molecular transfer hydrogenation process to generate inactive quinolin-4-ol. Subsequently, using air/oxygen as the terminal oxidant, the iodine anion was oxidized to I2 to regenerate the 3-iodoquinolin-4-ol from quinolin-4-ol in the catalytic cycle. Key benefits of this methodology include its simplicity, transition metal-free conditions, environmentally-benign oxidant, and high atom economy, making it a valuable approach for synthesizing medicinally significant 4-aminoquinoline derivatives.

Ligand-free nickel catalyzed perfluoroalkylation of arenes and heteroarenes

We describe a "ligand-free" Ni-catalyzed perfluoroalkylation of heteroarenes to produce a diverse array of trfiluoromethyl, pentafluoroethyl and heptafluoropropyl adducts. Catalysis proceeds at room temperature via a radical pathway. The catalytic protocol is distinguished by its simplicity, and its wide scope demonstrates the potential in the late-stage functionalization of drug analogues and peptides.

Copper-Catalyzed Reactions of Aryl Halides with N-nucleophiles and Their Possible Application for Degradation of Halogenated Aromatic Contaminants

This review summarizes recent applications of copper or copper-based compounds as a nonprecious metal catalyst in N-nucleophiles-based dehalogenation (DH) reactions of halogenated aromatic compounds (Ar-Xs). Cu-catalyzed DH enables the production of corresponding nonhalogenated aromatic products (Ar-Nu), which are much more biodegradable and can be mineralized during aerobic wastewater treatment or which are principally further applicable. Based on available knowledge, the developed Cu-based DH methods enable the utilization of amines for effective cleavage of aryl-halogen bonds in organic solvents or even in an aqueous solution.

Electrochemical-Oxidation-Promoted Direct N-ortho-Selective Difluoromethylation of Heterocyclic N-Oxides

An efficient and green electrochemical N-ortho-selective difluoromethylation method of various quinoline and isoquinoline N-oxides has been developed. In this method, sodium difluoromethanesulfinate (HCF₂SO₂Na) was used as the source of the difluoromethyl moiety, and various N-ortho-selective difluoromethylation quinoline and isoquinoline N-oxides were obtained in good to excellent yields under a constant current. In addition, the reaction was easy to scale up and maintained a good yield. Preliminary mechanism studies suggested that the reaction undergoes a free-radical addition and hydrogen elimination pathway.

Metal-catalyzed reactions for the C(sp2)–N bond formation: achievements of recent years

The review deals with the main catalytic methods for the C(sp2)–N bond formation, including Buchwald–Hartwig palladium-catalyzed amination of aryl and heteroaryl halides, renaissance of the Ullmann chemistry, i.e., the application of catalysis by copper complexes to form the carbon–nitrogen bond, and Chan–Lam reactions of (hetero)arylboronic acids with amines. Also, oxidative amination with C–H activation, which has been booming during the last decade, is addressed. Particular attention is paid to achievements in the application of heterogenized catalysts.

The bibliography includes 350 references.

Solvated Nickel Complexes as Stoichiometric and Catalytic Perfluoroalkylation Agents*

The acetonitrile-solvated [(MeCN)Ni(C₂ F₅ )₃ ]^- was prepared in order to compare and contrast its reactivity with the known [(MeCN)Ni(CF₃ )₃ ]^- towards organic electrophiles. Both [(MeCN)Ni(CF₃ )₃ ]^- and [(MeCN)Ni(C₂ F₅ )₃ ]^- successfully react with aryl iodonium and diazonium salts as well as alkynyl iodonium salts to give fluoroalkylated organic products. Electrochemical analysis of [(MeCN)Ni^II (C₂ F₅ )₃ ]^- suggests that, upon electro-oxidation to [(MeCN)_n Ni^III (C₂ F₅ )₃ ], reductive homolysis of a perfluoroethyl radical occurs, with the concomitant formation of [(MeCN)₂ Ni^II (C₂ F₅ )₂ ]. Catalytic C-H trifluoromethylations of electron-rich arenes were successfully achieved using either [(MeCN)Ni(CF₃ )₃ ]^- or the related [Ni(CF₃ )₄ ]^2- . Stoichiometric reactions of the solvated nickel complexes reveal that "ligandless" nickel is exceptionally capable of serving as reservoir of CF₃ groups under catalytically relevant conditions.

Solvent-Dependent Cyclization of 2-Alkynylanilines and ClCF2COONa for the Divergent Assembly of N-(Quinolin-2-yl)amides and Quinolin-2(1H)-ones

Herein, we present an expedient Cu-catalyzed [5 + 1] cyclization of 2-alkynylanilines and ClCF₂COONa to divergent construction of N-(quinolin-2-yl)amides and quinolin-2(1H)-ones by regulating the reaction solvents. Notably, nitrile acts as a solvent and performs the Ritter reactions. ClCF₂COONa is used as a C1 synthon in this transformation, which also represents the first example for utilization of ClCF₂COONa as an efficient desiliconization reagent. The current protocol involves in situ generation of isocyanide, copper-activated alkyne, Ritter reaction and protonation.

One-Pot Synthesis of Aminated Benzo-Fused Heterocycles and N-Substituted Dibenzothiophenes via Copper-Catalyzed Ullmann Type Reaction

We report here a direct and effective method to synthesize a primary amine of several polycyclic aromatic compounds. This reaction has been achieved through copper (I)-catalyzed Ullmann C-N coupling. Furthermore, this strategy allows the synthesis of new N-substituted dibenzothiophene derivatives through the coupling of 2-bromodibenzothiophene with various ranges of primary and secondary amines. The use of inexpensive catalysts, aqueous ammonia as the convenient source of ammonia and ligand free, makes this protocol environmentally and economically favorable for the synthesis of these compounds.

Transition-metal-free access to 2-aminopyridine derivatives from 2-fluoropyridine and acetamidine hydrochloride

Under catalyst-free conditions, an efficient method for the synthesis of 2-aminopyridine derivatives through the nucleophilic substitution and hydrolysis of 2-fluoropyridine and acetamidine hydrochloride has been developed. This amination uses inexpensive acetamidine hydrochloride as the ammonia source and has the advantages of a high yield, high chemoselectivity and wide substrate adaptability. The results suggest that other N-heterocycles containing fluorine substituents can also complete the reaction via these reaction conditions and yield the target products.

Palladium-Catalyzed Cyclization of N-Acyl- o-alkynylanilines with Isocyanides Involving a 1,3-Acyl Migration: Rapid Access to Functionalized 2-Aminoquinolines

A simple and expedient approach for the synthesis of functionalized 2-aminoquinolines via palladium-catalyzed annulation of N-acyl- o-alkynylanilines with isocyanides has been developed with high atom economy, in which an unconventional 6- endo-dig cyclization process is observed. Further investigations of the mechanism demonstrated that an intramolecular acyl migration of the N-protecting groups was involved in this transformation.

Tandem cyclization of o-alkynylanilines with isocyanides triggered by intramolecular nucleopalladation: access to heterocyclic fused 2-aminoquinolines

Herein, a novel strategy for the synthesis of various heterocyclic fused 2-aminoquinolines via palladium-catalyzed tandem cyclization of o-alkynylanilines with isocyanides has been developed. This process includes trans-oxy/aminopalladation, isocyanide insertion, elimination and 1,3-hydrogen migration. Besides high atom and step economy, this method shows good functional group compatibility with excellent chemo- and regioselectivities under mild reaction conditions.

In situ generation of ammonia for the copper-catalyzed synthesis of primary aminoquinolines

Primary aminoquinolines were synthesized from iodoquinolines in the presence of a copper(i) iodide catalyst and formamide as both solvent and source of ammonia generated in situ.

Mild and highly selective palladium-catalyzed monoarylation of ammonia enabled by the use of bulky biarylphosphine ligands and palladacycle precatalysts

A method for the Pd-catalyzed arylation of ammonia with a wide range of aryl and heteroaryl halides, including challenging five-membered heterocyclic substrates, is described. Excellent selectivity for monoarylation of ammonia to primary arylamines was achieved under mild conditions or at rt by the use of bulky biarylphosphine ligands (L6, L7, and L4) as well as their corresponding aminobiphenyl palladacycle precatalysts (3a, 3b, and 3c). As this process requires neither the use of a glovebox nor high pressures of ammonia, it should be widely applicable.