Metal-free N-arylation of secondary amides at room temperature

BODIPY(aryl)iodonium salts in the efficient synthesis of diversely functionalized BODIPYs and selective detection of serum albumin

BODIPY(aryl)iodonium salts were readily accessible from the high-yielding reaction of BODIPY with iodoarenes or hydroxyl(tosyloxy)iodoarenes in the presence of m-CPBA. The prepared BODIPY(aryl)iodonium salts bearing substituents of varied electronic nature were utilized for the direct syntheses of thiocyanate, azide, amine and acrylate functionalized BODIPYs and β,β'-bis-BODIPYs. The regioselective syntheses of α-piperidinyl and β-piperidinyl substituted BODIPYs were achieved through the reaction of BODIPY(aryl)iodonium salts with piperidine in the absence and presence of copper(I). Expeditious and high yielding (79-82%) synthesis of β,β'-bis-BODIPYs was also developed through the palladium-catalyzed reductive coupling of the easily accessible BODIPY(aryl)iodonium salts. Some of the indole-appended BODIPYs and bis-BODIPYs displayed strong absorption in the visible region (∼610 nm). The BODIPY(aryl)iodonium salts also showed significant binding with serum albumin and were observed to be selective serum protein sensors with estimated limits of detection as low as 7 μg mL-1 in some cases.

Copper-Catalyzed Chemoselective O-Arylation of Oxindoles: Access to Cyclic Aryl Carboxyimidates

We have developed a highly efficient base- and additive-free chemoselective CuO-catalyzed strategy for the O-arylation of 2-oxindoles to synthesize 2-phenoxy-3H-indole and 2-phenoxy-1H-indole derivatives in the presence of diaryl iodonium salts. This method offers a variety of O-arylated oxindoles in good to excellent yields under relatively milder reaction conditions. Furthermore, this methodology was extended for the O-arylation of 2-pyridinone and isoindoline-1-one derivatives as well.

Exploiting the Marcus inverted region for first-row transition metal-based photoredox catalysis

Second- and third-row transition metal complexes are widely employed in photocatalysis, whereas earth-abundant first-row transition metals have found only limited use because of the prohibitively fast decay of their excited states. We report an unforeseen reactivity mode for productive photocatalysis that uses cobalt polypyridyl complexes as photocatalysts by exploiting Marcus inverted region behavior that couples increases in excited-state energies with increased excited-state lifetimes. These cobalt (III) complexes can engage in bimolecular reactivity by virtue of their strong redox potentials and sufficiently long excited-state lifetimes, catalyzing oxidative C(sp2)-N coupling of aryl amides with challenging sterically hindered aryl boronic acids. More generally, the results imply that chromophores can be designed to increase excited-state lifetimes while simultaneously increasing excited-state energies, providing a pathway for the use of relatively abundant metals as photoredox catalysts.

Metal-Free Chemoselective S-Arylation of Sulfenamides To Access Sulfilimines

A novel and efficient S-arylation of sulfenamides with diaryliodonium salts for the synthesis of sulfilimines is developed. The reaction proceeds smoothly under transition-metal-free and air conditions, giving rapid access to sulfilimines in good to excellent yields via selective S-C bond formation. This protocol is scalable and exhibits a broad substrate scope, good functional group tolerance, and excellent chemoselectivity.

Utilization of Aryl(TMP)iodonium Salts for Copper-Catalyzed N-Arylation of Isatoic Anhydrides: An Avenue to Fenamic Acid Derivatives and N,N'-Diarylindazol-3-ones

Herein, we report a general method for copper-catalyzed N-arylation of isatoic anhydrides with unsymmetrical iodonium salts at room temperature. The developed catalytic protocol is mild and operationally simple, and aryl(TMP)iodonium trifluoroacetate is employed as the arylating partner. The methodology offers the broad applicability of both structurally and electronically diverse aryl groups from aryl(TMP)iodonium salts to access N-arylated isatoic anhydrides in moderate to excellent yields (53-92%). Moreover, the substituted isatoic anhydrides are equally compatible with the protocol too. To demonstrate the synthetic utilities of the N-arylation process, we also report an alternative approach for biologically relevant fenamic acid derivatives and N,N'-diarylindazol-3-ones in a one-pot step economical system. In addition, the scale-up synthesis of flufenamic acid is also illustrated.

Selective Hydrolysis of Primary and Secondary Amides Enabled by Visible Light

Amide hydrolysis is a fundamentally important transformation in organic chemistry. Developing hydrolysis procedures under mild conditions with a broad substrate scope is desirable. Herein, by leveraging a photoresponsive auxiliary o-nitroanilide, we established a mild two-step protocol for the hydrolysis of primary and secondary amides. This protocol is driven by visible light irradiation at room temperature under neutral conditions, which tolerates numerous acid- and base-sensitive functional groups. Various drugs, natural product-, and amino acid-derived amides can be selectively hydrolyzed.

Synthesis of 3-(2-oxopropyl)-2-arylisoindolinone derivatives via a three-component reaction of diaryliodonium salts with 2-formylbenzonitriles and phenylacetylenes

A copper-catalyzed multicomponent cascade cyclization using readily available substrates, including 2-formylbenzonitriles, phenylacetylenes, and diaryliodonium salts, is achieved. A broad reaction scope is presented with good functional group compatibility, giving rise to a range of 3-(2-oxopropyl)-2-arylisoindolinones in moderate to good yields.

Visible Light Photoredox-Catalyzed Direct C-H Arylation of Quinoxalin-2(1H)-ones with Diaryliodonium Salts

A photoredox-catalyzed direct arylation of quinoxalin-2-(1H)-ones using diaryliodonium triflates as the convenient, stable, and cheap aryl source is described. A broad variety of quinoxalin-2-(1H)-ones are shown to react with structurally and electronically diverse diaryliodonium triflates, allowing efficient access to a wide variety of pharmaceutically important 3-arylquinoxalin-2-(1H)-ones. The presented method is attractive with regard to operational simplicity, mild conditions, broad scope, scalability, and high functional group tolerance.

Organocatalytic Synthesis of Phenols from Diaryliodonium Salts with Water under Metal-Free Conditions

The metal-free synthesis of phenols from diaryliodonium salts with water was developed by using N-benzylpyridin-2-one as an organocatalyst. In this process, sterically congested, functionalized, and heterocycle-containing iodonium salts were smoothly converted to the desired products, and the clofibrate and mecloqualone derivatives were also synthesized in high yields. In addition, the gram-scale experiment was successfully carried out with 10 mmol of a sterically congested substrate.

Tandem cyclization/arylation of diaryliodoniums via in situ constructed benzoxazole as a directing group for atom-economical transformation

Linear diaryliodoniums often undergo only single arylation and leave equivalent aryl iodide as waste.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Diaryliodonium Salt-Based Synthesis of N-Alkoxyindolines and Further Insights into the Ishikawa Indole Synthesis

A diaryliodonium salt-based strategy enabled the first systematic synthesis of rarely accessible N-alkoxyindolines. Mechanistic analyses suggested that the reaction likely involves reductive elimination of iodobenzene from iodaoxazepine via a four-membered transition state, followed by Meisenheimer rearrangement. Substrates with N-carbamate protection afforded indole in a manner similar to that of the Ishikawa indole synthesis. Preinstallation of a stannyl group as an iodonium salt precursor greatly expanded the substrate scope, and further mechanistic insights are discussed.

Multicomponent Synthesis of Biologically Relevant S-Aryl Dithiocarbamates Using Diaryliodonium Salts

A transition-metal-free one-pot three-component annulation between diaryliodonium triflates, cyclic and acyclic aliphatic amines, and carbon disulfide providing a convenient and efficient access to biologically relevant S-aryl dithiocarbamates is developed. The reaction does not require metal, base, or any other additive and operates under mild and ambient conditions. This methodology is robust, scalable, and exhibits a broad substrate scope. The in silico analysis revealed that the majority of the compounds have a drug-likeness and good ADMET characteristics.

O-Cyclopropyl hydroxylamines: gram-scale synthesis and utility as precursors for N-heterocycles

O-Cyclopropyl hydroxylamines, now accessible via a novel and scalable synthetic route, have been demonstrated to be bench-stable and practical precursors for the synthesis of N-heterocycles via a di-heteroatom [3,3]-sigmatropic rearrangement. In order to study the reactivity of these compounds in depth, a robust synthesis of both ring-substituted and ring-unsubstituted O-cyclopropyl hydroxylamines has been developed. Metal-free conditions for the facile N-arylation of these precursors were also identified. It was found that the N-arylated O-cyclopropyl hydroxamates can efficiently undergo a one-pot [3,3]-sigmatropic rearrangement/cyclization/rearomatization cascade under base-mediated conditions to furnish a structurally diverse set of substituted tetrahydroquinolines.

Recent Advances in Transition-Metal-Free Late-Stage C-H and N-H Arylation of Heteroarenes Using Diaryliodonium Salts

Transition-metal-free direct arylation of C-H or N-H bonds is one of the key emerging methodologies that is currently attracting tremendous attention. Diaryliodonium salts serve as a stepping stone on the way to alternative environmentally friendly and straightforward pathways for the construction of C-C and C-heteroatom bonds. In this review, we emphasize the recent synthetic advances of late-stage C(sp2)-N and C(sp2)-C(sp2) bond-forming reactions under metal-free conditions using diaryliodonium salts as arylating reagent and its applications to the synthesis of new arylated bioactive heterocyclic compounds.

Direct para-Selective C-H Amination of Iodobenzenes: Highly Efficient Approach for the Synthesis of Diarylamines

Iodine(III)-mediated synthesis of 4-iodo-N-phenylaniline from iodobenzene has been achieved, and the reaction can proceed under mild conditions. A variety of functional groups were well tolerated, providing the corresponding products in moderate to good yields. The remaining iodine group provides an effective platform for converting the products into several valuable asymmetric diphenylamines. Most importantly, this reaction can be easily scaled up to the ten-gram scale, highlighting its synthetic utility. The mechanistic study revealed that the in situ generated aryl hypervalent iodine intermediate is the key factor to realize this para-selective C-H amination reaction.

Copper-catalyzed transformation of alkyl nitriles to N-arylacetamide using diaryliodonium salts

This work reports a simple and efficient method for the copper-catalyzed redox-neutral transformation of alkyl nitriles using eco-friendly diaryliodonium salts and leading to N-arylacetamides. The method features high efficiency, broad substrate scope and good functional group tolerance.

N-Alkenylation of hydroxamic acid derivatives with ethynyl benziodoxolone to synthesize cis-enamides through vinyl benziodoxolones

The stereoselective synthesis of cis-β-N-alkoxyamidevinyl benziodoxolones (cis-β-N-RO-amide-VBXs) from O-alkyl hydroxamic acids in the presence of an ethynyl benziodoxolone-acetonitrile complex (EBX-MeCN) is reported herein. The reaction was performed under mild conditions including an aqueous solvent, a mild base, and room temperature. The reaction tolerated various O-alkyl hydroxamic acids derived from carboxylic acids, such as amino acids, pharmaceuticals, and natural products. Vinyl dideuterated cis-β-N-MeO-amide-VBXs were also synthesized using deuterium oxide as the deuterium source. Valine-derived cis-β-N-MeO-amide-VBX was stereospecifically derivatized to hydroxamic acid-derived cis-enamides without the loss of stereoselectivity or reduction in the deuterium/hydrogen ratio.

Nucleophilic Aromatic Substitution of Polyfluoroarene to Access Highly Functionalized 10-Phenylphenothiazine Derivatives

Nucleophilic aromatic substitution (S_NAr) reactions can provide metal-free access to synthesize monosubstituted aromatic compounds. We developed efficient S_NAr conditions for p-selective substitution of polyfluoroarenes with phenothiazine in the presence of a mild base to afford the corresponding 10-phenylphenothiazine (PTH) derivatives. The resulting polyfluoroarene-bearing PTH derivatives were subjected to a second S_NAr reaction to generate highly functionalized PTH derivatives with potential applicability as photocatalysts for the reduction of carbon–halogen bonds.

Oxidative cross-dehydrogenative coupling between iodoarenes and acylanilides for C–N bond formation under metal-free conditions

A metal-free oxidative cross-dehydrogenative coupling between iodoarenes and acylanilides was developed. It gave highly para-selectivie C–N coupling products with the retention of iodine atom which enables further transformations.

Utilization of Unsymmetric Diaryliodonium Salts in α-Arylation of α-Fluoroacetoacetamides

The use of unsymmetric diaryliodonium salts as a versatile class of arylating agents has been demonstrated by developing a novel strategy to quickly access α-arylated α-fluoroacetoacetamides. The protocol provides a convenient metal-free method for the α-arylation of a diverse class of fluorinated acetoacetamides, and the products are obtained in good yields. The strategy, upon use of electron-deficient diaryliodonium salts as an arylating agent, provides α-fluoroacetamides through a spontaneous arylation/deacylation cascade.

N- and O-arylation of pyridin-2-ones with diaryliodonium salts: base-dependent orthogonal selectivity under metal-free conditions

Metal-free N- and O-arylation reactions of pyridin-2-ones as ambident nucleophiles have been achieved with diaryliodonium salts on the basis of base-dependent chemoselectivity. In the presence of N,N-diethylaniline in fluorobenzene, pyridin-2-ones were very selectively converted to N-arylated products in high yields. On the other hand, the O-arylation reactions smoothly proceeded with the use of quinoline in chlorobenzene, leading to high yields and selectivities. In these methods, a variety of pyridin-2-ones in addition to pyridin-4-one and a set of diaryliodonium salts were accepted as suitable reaction partners.

Bimetallic Catalyzed N-arylation Used in Synthesis of Novel β-carbolines Derivatives

Background:

Natural occurring β-Carbolines alkaloids are abundant in the plant kingdom or other organisms, and they were found to possess good antitumor activity through multiple mechanisms. Based on previous summarized SARs of β-carboline derivatives, the modification on pyridine ring would have a great impact on their antitumor activities. Therefore, we plan to synthesized arylated β-carboline-3-amides to find more valuable β-Carbolines derivatives.

Methods:

A novel bimetallic Pd(OAc)2/AgOAc catalyst system was developed for the amidation of aryl iodides under acid condition. A series of N-arylated β-carbolines derivatives were synthesized using this method. The structures of these compounds were confirmed by 1H NMR, 13C NMR and HRMS, and their in vitro antiproliferative activity was investigated against HepG2 and Hela tumor cell lines by MTT assay.

Results:

Eleven N-arylated β-carboline-3-amides were synthesized using this bimetallic catalyzed method in 58-98% yields. These synthesized N-arylated compounds showed no antiproliferative activity at 20 μM.

Conclusion:

We have discovered an efficient and bimetallic catalytic system allowing the Narylation of secondary acyclic amides. This is the first report that N-arylation of aliphatic secondary acyclic amides under acid condition.

Metal-free α-arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts

Herein, we present a mild and efficient metal-free arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts. A broad range of diaryliodonium salts and α-fluoro-α-nitroacetamides containing sensitive functional groups was successfully employed in this protocol to yield the arylated products in good yields. The synthetic value of this novel protocol was further highlighted by extending the α-arylation to α-cyano-α-fluoroacetamides.

Transition-Metal-Free N-Arylation of Amines by Triarylsulfonium Triflates

A simple and efficient method for transition-metal-free N-arylation of various amines by triarylsulfonium triflates is described. Both aliphatic and aromatic amines were smoothly converted at 80 °C in the presence of tBuOK or KOH to give the corresponding mono N-arylated products in good to high yields. The molar ratios of the reactants and the choice of bases had a big effect on the reaction. When a large excess of [Ph₃ S][OTf] and tBuOK were employed for primary amines under the standard conditions, the bis(N-phenyl) products were predominantly formed. This method was also applicable to the synthesis of bioactive N-phenyl amino acid derivatives. The control experiments, the deuterium labelling study, and the presence of regioisomers of N-arylated products when using 4-substituted triarylsulfonium triflates suggested that the reaction might proceed through an aryne intermediate. The present protocol demonstrated that triarylsulfonium salts are versatile arylation reagents in the construction of C_Ar -N bonds.

Sterically Congested 2,6-Disubstituted Anilines from Direct C-N Bond Formation at an Iodine(III) Center

2,6‐Disubstituted anilines are readily prepared from the direct reaction between amides and diaryliodonium salts. As demonstrated for 24 different examples, the reaction is of unusually broad scope with respect to the sterically congested arene and the nitrogen source, occurs without the requirement for any additional promoter, and proceeds through a direct reductive elimination at the iodine(III) center. The efficiency of the coupling procedure is further demonstrated within the short synthesis of a chemerin binding inhibitor.

Regiospecific N-Arylation of Aliphatic Amines under Mild and Metal-Free Reaction Conditions

A transition metal‐free N‐arylation of primary and secondary amines with diaryliodonium salts is presented. Both acyclic and cyclic amines are well tolerated, providing a large set of N‐alkyl anilines. The methodology is unprecedented among metal‐free methods in terms of amine scope, the ability to transfer both electron‐withdrawing and electron‐donating aryl groups, and efficient use of resources, as excess substrate or reagents are not required.

Metal-free formal synthesis of phenoxazine

A transition metal-free formal synthesis of phenoxazine is presented. The key step of the sequence is a high-yielding O-arylation of a phenol with an unsymmetrical diaryliodonium salt to provide an ortho-disubstituted diaryl ether. This species was cyclized to acetylphenoxazine in moderate yield. The overall yield in the three-step sequence is 72% based on recovered diaryl ether. An interesting, unusually stable iodine(III) intermediate in the O-arylation was observed by NMR and could be converted to the product upon longer reaction time.

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

Hypervalent iodine reagents have been developed as highly valuable reagents in synthetic organic chemistry during the past few decades. These reagents have been identified as key replacements of various toxic heavy metals in organic synthesis. Various synthetically and biologically important scaffolds have been developed using hypervalent iodine reagents either in stoichiometric or catalytic amounts. In addition, hypervalent iodine reagents have been employed for the synthesis of spirocyclic scaffolds via dearomatization processes. In this review, various approaches for the synthesis of spirocyclic scaffolds using hypervalent iodine reagents are covered including their stereoselective synthesis. Additionally, the applications of these reagents in natural product synthesis are also covered.

One-pot synthesis of diaryliodonium salts from arenes and aryl iodides with Oxone-sulfuric acid

A facile synthesis of diaryliodonium salts utilizing Oxone as versatile and cheap oxidant has been developed. This method shows wide applicability and can be used for the preparation of iodonium salts containing electron-donating or electron-withdrawing groups in good yields. In addition, this procedure can be applied to the preparation of symmetric iodonium salts directly from arenes via a one-pot iodination-oxidation sequence.

Lewis Acid-Mediated Room-Temperature Cascade Reaction of 3-Hydroxyisoindolin-1-one with Alkynes

An efficient and mild synthesis of a variety of 3-(2-oxopropyl)-isoindolinone derivatives via a BF₃·Et₂O catalyzed cascade reaction among 3-hydroxyisoindolin-1-one and phenylacetylene was achieved. Various isoindolinone derivatives were obtained in good to excellent yields. The process, which avoided several drawbacks such as the requirement of concentrated protic acids and metal catalysts, protecting group of nitrogen, high temperature, and multistep synthesis, includes C(sp³)-OH cleavage, C-C coupling, and hydration of alkyne.

Additive-Free Pd-Catalysed C-2 Arylation of Tryptophan Derivatives with Diaryliodonium Salts

An efficient, mild and Pd-catalysed C-2 arylation of Fmoc-L-tryptophan with diaryliodonium salts has been developed, giving easy access to C-2 arylated tryptophan derivatives. This protocol tolerates a variety of functional groups and proceeds smoothly in high yields without any additives. In addition, the chemoseletive C–H arylation with unsymmetrical salts is described.

SF5-Pyridylaryl-λ3-iodonium salts and their utility as electrophilic reagents to access SF5-pyridine derivatives in the late-stage of synthesis

Electrophilic pentafluorosulfanyl (SF₅) heteroarylation of target molecules using novel reagents is described. Unsymmetrical diaryliodonium reagents 1 having 2-SF₅-pyridine have been synthesized in good yields. They are efficient electrophilic reagents for carbon and heterocentered nucleophiles, producing the corresponding SF₅-pyridine derivatives in good to excellent yields.

Metal-free regioselective formation of C-N and C-O bonds with the utilization of diaryliodonium salts in water: facile synthesis of N-arylquinolones and aryloxyquinolines

Regioselective construction of crucial C-N and C-O bonds leading to N-arylquinolones and aryloxyquinolines has been accomplished by employing easily accessible diaryliodonium salts and quinolones in water under metal- and ligand-free conditions. This operationally simple strategy is significant due to mild reaction conditions, high product yields, recyclability of released iodoarenes and scalability to the gram level. The practical utility of the developed protocol was proved by the arylation of medicinally important heterocycles like acridin-9(10H)-one, 3-methylquinoxalin-2(1H)-one and 1H-benzo[d]imidazol-2(3H)-one.