A transition-metal-free synthesis of arylcarboxyamides from aryl diazonium salts and isocyanides

General Approach to Amides through Decarboxylative Radical Cross-Coupling of Carboxylic Acids and Isocyanides

Herein, we report a silver-catalyzed protocol for decarboxylative cross-coupling between carboxylic acids and isocyanides, leading to linear amide products through a free-radical mechanism. The disclosed approach provides a general entry to a variety of decorated amides, accommodating a diverse array of radical precursors, including aryl, heteroaryl, alkynyl, alkenyl, and alkyl carboxylic acids. Notably, the protocol proved to be efficient for decarboxylative late-stage functionalization of several elaborate pharmaceuticals, demonstrating its potential applications.

Arylazo sulfones: multifaceted photochemical reagents and beyond

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-N2SO2R) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, viz. aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).

Dual Role of Oxoaldehydes: Divergent Synthesis of 3-Aryl- and 3-Aroylcoumarins

A facile and efficient synthetic approach to various valuable 3-aryl- and 3-aroylcoumarins by the direct arylation and aroylation of coumarins with glyoxals in a metal-free manner is presented. The aryl glyoxal is for the first time recognized to serve as an aryl surrogate in addition to its role as an aroyl transfer reagent via a simple switch in reaction conditions. The approach accommodates a broad substrate scope and high yields of the two types of cross-coupling reactions starting from identical starting materials.

Photochemical regioselective C–H arylation of imidazo[1,2-a]pyridine derivatives using chlorophyll as a biocatalyst and diazonium salts

This communication describes the development of a mild method for the arylation of imidazo[1,2-a]pyridine with diazonium salt derivatives and using chlorophyll as a biocatalyst via visible-light catalysis.

Direct C-H aminocarbonylation of N-heteroarenes with isocyanides under transition metal-free conditions

A C-C bond forming amide synthesis through direct C-H aminocarbonylation of N-heteroarenes with isocyanides was developed. The reaction was mediated by an inorganic persulfate salt under transition metal-free conditions. Mechanistic studies suggested a radical pathway for this reaction without the participation of H₂O and O₂. This method also showed merits of substrate availability, easy operation and atom economy. It provided an efficient route for straightforward synthesis of N-heteroaryl amides.

Nickel-Catalyzed Formal Aminocarbonylation of Unactivated Alkyl Iodides with Isocyanides

Herein, we disclose a Ni-catalyzed formal aminocarbonylation of primary and secondary unactivated aliphatic iodides with isocyanides to afford alkyl amide, which proceeds via the selective monomigratory insertion of isocyanides with alkyl iodides, subsequent β-hydride elimination, and hydrolysis process. The reaction features wide functional group tolerance under mild conditions. Additionally, the selective, one-pot hydrolysis of reaction mixture under acid conditions allows for expedient synthesis of the corresponding alkyl carboxylic acid.

Chlorophyll-catalyzed photochemical regioselective coumarin C–H arylation with diazonium salts

A metal-free, direct C–H arylation of coumarins with aryl diazonium salts at room temperature using chlorophyll as a green photosensitizer is devised.

Gold redox catalysis for cyclization/arylation of allylic oximes: synthesis of isoxazoline derivatives

Base-assisted diazonium activation has been employed to promote gold(i)/(iii) redox catalysis toward allylic oxime cyclization/aryl coupling. Functional isoxazolines were prepared with good to excellent yields, while the alternative photoactivation method provided trace amounts of the isoxazoline products. This study further broadens the scope of gold redox chemistry.

Iodine-Catalyzed Odorless Synthesis of S-Thiocarbamates with Sulfonyl Chlorides as a Sulfur Source

A general and efficient protocol for the direct preparation of various S-thiocarbamates with readily available and inexpensive sulfonyl chlorides as an odorless sulfur source was developed. The employment of easily available reactants, excellent functional group tolerability, and mild reaction conditions make this process very practical.

Molecular iodine-mediated synthesis of thiocarbamates from thiols, isocyanides and water under metal-free conditions

A simple and practical molecular iodine-mediated method for the efficient construction of thiocarbamates from isocyanides, thiols and water under metal-free and mild conditions has been developed. A variety of thiocarbamates were easily synthesized through this methodology, which has the advantages of simple operation, eco-friendly conditions, good functional group tolerance, and readily accessible raw materials.

A radical approach to the copper oxidative addition problem: Trifluoromethylation of bromoarenes

Transition metal-catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper's capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical-capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.

Gold promoted arylative cyclization of alkynoic acids with arenediazonium salts

Arylgold(iii) species generated from arenediazonium salts and Au(i) under thermal conditions promote the arylative cyclization of alkynoic acids leading to tetrasubstituted lactones.

Aromatic substitutions of arenediazonium salts via metal catalysis, single electron transfer, and weak base mediation

Radical aromatic substitutions of arenediazonium salts can be initiated by various methods. The recent developments of weak base-mediated protocols provide great advantages over conventional metal-mediated or photoredox reactions by their operational simplicity, price, hazard potential and scalability.

Gold Redox Catalysis through Base-Initiated Diazonium Decomposition toward Alkene, Alkyne, and Allene Activation

The discovery of photoassisted diazonium activation toward gold(I) oxidation greatly extended the scope of gold redox catalysis by avoiding the use of a strong oxidant. Some practical issues that limit the application of this new type of chemistry are the relative low efficiency (long reaction time and low conversion) and the strict reaction condition control that is necessary (degassing and inert reaction environment). Herein, an alternative photofree condition has been developed through Lewis base induced diazonium activation. With this method, an unreactive AuI catalyst was used in combination with Na2 CO3 and diazonium salts to produce a AuIII intermediate. The efficient activation of various substrates, including alkyne, alkene and allene was achieved, followed by rapid AuIII reductive elimination, which yielded the C-C coupling products with good to excellent yields. Relative to the previously reported photoactivation method, our approach offered greater efficiency and versatility through faster reaction rates and broader reaction scope. Challenging substrates such as electron rich/neutral allenes, which could not be activated under the photoinitiation conditions (<5 % yield), could be activated to subsequently yield the desired coupling products in good to excellent yield.

Palladium/Copper-Catalyzed Oxidative Coupling of Arylboronic Acids with Isocyanides: Selective Routes to Amides and Diaryl Ketones

An efficient and alternative oxidative cross-coupling strategy starting from arylboronic acids and isocyanides for the selective synthesis of amides and diaryl ketones with palladium/copper catalysis is developed. Various substituted benzamides and benzophenones could be obtained in good yields. The reaction represents an efficient and alternative strategy for the synthesis of carbonyl compounds.

Direct carboxamidation of cyclic 2-diazo-1,3-diketones by Rh2(OAc)4-catalyzed isocyanide insertion–hydrolysis

A novel and efficient strategy for the synthesis of 2-hydroxy-6-oxocyclohex-1-enecarboxamides through a Rh₂(OAc)₄-catalyzed direct carboxamidation of cyclic 2-diazo-1,3-diketones has been developed.

Silver-mediated radical coupling reaction of isocyanides and alcohols/phenols in the presence of water: unprecedented hydration and radical coupling reaction sequence

The first radical coupling of isocyanides and alcohols/phenols promoted by silver in the presence of water is reported.

Palladium-catalyzed chemoselective synthesis of indane-1,3-dione derivatives via tert-butyl isocyanide insertion

A simple and efficient strategy for the synthesis of indane-1,3-dione derivatives through a palladium(0)-catalyzed reaction incorporating tert-butyl isocyanide has been developed. In addition, by applying this protocol as the key step, indenopyrazole derivatives can be easily synthesized in high yields in a one-pot procedure. This methodology is tolerant of a wide range of substrates and applicable to library synthesis.

Recent progress in imidoyl radical-involved reactions

This review discusses the recent progress in imidoyl radical-involved reactions including the synthesis of functionalized heterocycles, nitriles, imines, amines,etc.

Palladium-Catalyzed Domino Synthesis of 4-Amino-3-acyl-2- naphthols via Isocyanide Chemoselective Insertion

A novel and efficient strategy for the synthesis of sterically hindered 4-amino-3-acyl-2-naphthols through a palladium-catalyzed coupling reaction involving isocyanide chemselective insertion and domino isomerization has been developed. The methodology, which is in accordance with the principle of "atom and step economy", efficiently constructs 4-amino-3-acyl-2-naphthols in moderate to good yields.

Silver-Catalyzed Cross-Coupling of Isocyanides and Active Methylene Compounds by a Radical Process

Isocyanides are versatile building blocks, and have been extensively exploited in C-H functionalization reactions. However, transition-metal-catalyzed direct C-H functionalization reactions with isocyanides suffer from over-insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross-coupling of isocyanides with active methylene compounds through silver-catalysis. The method solves the over-insertion issue and affords a variety of otherwise difficult to synthesize β-aminoenones and tricarbonylmethanes under base- and ligand-free conditions. This report presents a new fundamental C-C bond-forming reaction of two basic chemicals.

Double functionalization of 2-amino-2′-hydroxy-1,1′-biaryls: synthesis of 4-nitro-dibenzofurans and benzofuro-indoles

A TM-free double functionalization of 2-amino-2′-hydroxy-1,1′-biaryls (see Scheme above) has been presented for the synthesis of 4-nitro-dibenzofurans.

Metal-free C(3)–H arylation of coumarins promoted by catalytic amounts of 5,10,15,20-tetrakis(4-diethylaminophenyl)porphyrin

Metal-free, Meerwein-type C(3)–H arylation of coumarins was achieved in the presence of catalytic amounts of 5,10,15,20-tetrakis(4-diethylaminophenyl)porphyrin.

When aryldiazonium salts meet vinyl diazoacetates: a cobalt-catalyzed regiospecific synthesis of N-arylpyrazoles

A cobalt-catalyzed C-N bond formation between aryl diazonium salts and vinyl diazoacetates has been developed under relatively mild conditions. The N-arylpyrazoles have been prepared in moderate to high yields in a regiospecific way.