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

Access to N-Aryl (Iso)quinolones via Aryne-Induced Three-Component Coupling Reaction

N-Aryl (iso)quinolones are of increasing interest in material and medicinal chemistry, although general routes for their provision remain underexplored, especially when compared with its N-alkyl counterparts. Herein, we report a modular and transition-metal-free, aryne-induced three-component coupling protocol that allows the facile synthesis of structurally diverse N-aryl (iso)quinolones from readily accessible halo-(iso)quinolines in the presence of water. Preliminary results highlight the applicability of our method through scale-up synthesis, downstream derivatization, and flexible synthesis involving other types of aryne precursors.

P(NMe2)3-Mediated Regioselective N-Alkylation of 2-Pyridones via Direct Deoxygenation of α-Keto Esters

A practical and regioselective direct N-alkylation of 2-pyridones is enabled by use of α-keto esters in the P(NMe2)3-mediated deoxygenation process. The reaction proceeds under mild conditions to produce N-alkylated 2-pyridones with high selectivity and generality, and the protocol is shown to be applicable for the scale-up synthesis, which makes it promising for practical applications.

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.

Diversification of Complex Diaryl Ethers via Diaryliodonium Intramolecular Aryl Rearrangement

In this study, we present an efficient site-selective O-arylation method applicable to a broad range of complex arenes involving intramolecular aryl rearrangement. The reaction was facilitated by diaryliodonium salts bearing vicinal trifluoromethanesulfonate (OTf) groups. The procedure was initiated with selective C-H bond activation of arenes, which were then converted into diaryl ethers through nucleophilic aromatic substitution (SNAr). This synthetic method successfully affords complex diaryl ether derivatives, showcasing its practicality for the diversification of functionalized arenes and pharmaceutical agents.

Rh(II)-Catalyzed Synthesis of N-Aryl 2-pyridone Using 2-Oxypyridine and Diazonaphthoquinone Via 1,6-Benzoyl Migratory Rearrangement

A Rh(II)-catalyzed simple and efficient synthesis of N-arylated 2-pyridone derivatives is described using 2-oxypyridine and diazonaphthoquinone as coupling partners. The reaction proceeds through the insertion of the nitrogen atom of the 2-oxypyridine derivative into quinoid carbene and subsequent 1,6-benzoyl migratory rearrangement. The reaction is broadened with sufficient scope and has the potential to offer axially chiral N-arylated 2-pyridone derivatives under suitable asymmetric conditions.

Rhodium-Catalyzed N-Arylation of 2-Pyridones Enabled by 1,6-Acyl Migratory Rearrangement of 2-Oxypyridines

An efficient rhodium-catalyzed dearomative rearrangement of 2-oxypyridines with quinone diazides has been developed for the direct synthesis of N-arylated pyridones, in which a novel 1,6-O-to-O rather than 1,4-O-to-C acyl rearrangement has been achieved under mild reaction conditions.

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.

Umpolung Synthesis of Pyridyl Ethers by BiV -Mediated O-Arylation of Pyridones

We report that O-selective arylation of 2- and 4-pyridones with arylboronic acids is affected by a modular, bismacycle-based system. The utility of this umpolung approach to pyridyl ethers, which is complementary to conventional methods based on S_N Ar or cross-coupling, is demonstrated through the concise synthesis of Ki6783 and picolinafen, and the formal synthesis of cabozantib and golvatinib. Computational investigations reveal that arylation proceeds in a concerted fashion via a 5-membered transition state. The kinetically-controlled regioselectivity for O-arylation-which is reversed relative to previous Bi^V -mediated pyridone arylations-is attributed primarily to the geometric constraints imposed by the bismacyclic scaffold.

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.

Rhodium-NHC-Catalyzed gem-Specific O-Selective Hydropyridonation of Terminal Alkynes

The dinuclear complex [Rh(μ-Cl)(η² -coe)(IPr)]₂ is an efficient catalyst for the O-selective Markovnikov-type addition of 2-pyridones to terminal alkynes. DFT calculations support a hydride-free pathway entailing intramolecular oxidative protonation of a π-alkyne by a κ¹ N-hydroxypyridine ligand. Subsequent O-nucleophilic attack on a metallacyclopropene species affords an O-alkenyl-2-oxypyridine chelate rhodium intermediate as the catalyst resting state. The release of the alkenyl ether is calculated as the rate-determining step.

Coordination effect enabled palladium-catalyzed regioselective O-alkylation of 2-pyridones

A novel tactic for the regioselective O-alkylation of 2-pyridones has been realized through palladium catalysis in moderate to high yields. The coordination effect between palladium and nitrogen on the pyridine ring plays a versatile role.

Updates on hypervalent-iodine reagents in metal-free organic synthesis

Hypervalent iodine (HVI) chemistry is a rapidly growing subdomain of contemporary organic chemistry because of its enormous synthetic applications. The high nucleofugality of the phenyliodonio group (I+Ph) and their radical...

Orbital analysis of bonding in diarylhalonium salts and relevance to periodic trends in structure and reactivity

Diarylhalonium compounds provide new opportunities as reagents and catalysts in the field of organic synthesis. The three center, four electron (3c–4e) bond is a center piece of their reactivity, but structural variation among the diarylhaloniums, and in comparison with other λ³-iodanes, indicates that the model needs refinement for broader applicability. We use a combination of Density Functional Theory (DFT), Natural Bond Orbital (NBO) Theory, and X-ray structure data to correlate bonding and structure for a λ³-iodane and a series of diarylchloronium, bromonium, and iodonium salts, and their isoelectronic diarylchalcogen counterparts. This analysis reveals that the s-orbital on the central halogen atom plays a greater role in the 3c–4e bond than previously considered. Finally, we show that our revised bonding model and associated structures account for both kinetic and thermodynamic reactivity for both acyclic phenyl(mesityl)halonium and cyclic dibenzohalolium salts.

A revised bonding model for diarylhalonium salts, that involves partial s-orbital contribution, provides new insight into periodic trends in structure and reactivity.

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...

Synthesis of 1-(1-Arylvinyl)pyridin-2(1H)-ones from Ketones and 2-Fluoropyridine

We describe a simple and efficient procedure for the synthesis of N-vinyl-substituted pyridones from ketones and 2-fluoropyridine in the presence of trifluoromethane sulfonic anhydride, followed by a base treatment. Various ketones with electron-donating or electron-withdrawing groups at the benzene rings can be used in this reaction. A preliminary mechanistic study indicates that it is not very likely that both vinyl triflates and vinyl cations play major roles as intermediates in this transformation.

A Mild and Highly Diastereoselective Preparation of N-Alkenyl-2-Pyridones via 2-Halopyridinium Salts and Aldehydes

An experimentally simple one-pot preparation of N-alkenyl-2-pyridones is reported. The reaction features mild conditions using readily available 2-halopyridinium salts and aldehydes. N-Alkenyl-2-pyridone formation proceeds with high diastereoselectivity, and a wide range of aldehyde reaction partners is tolerated. Pyridone products are also amenable to further manipulation, including conversion to N-alkyl pyridones and polycyclic ring systems.

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.

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.

Recent developments in selective N-arylation of azoles

Transition-metal based carbon-heteroatom (C-X) bond formation has attracted the attention of synthetic chemists over the past few years because the resultant aryl/heteroaryl motifs are important substructures in many natural products, pharmaceuticals, etc. Several efficient protocols such as Buchwald-Hartwig amination, Ullmann coupling, Chan-Lam coupling and metal-free approaches have proved beneficial in C-X bond formation. Selective arylation of one hetero-centre over other centres without protection/deprotection thus allowing minimum synthetic manipulation has been achieved for several substrates using these protocols. Azoles are one such novel five-membered heterocyclic core with huge pharmaceutical applications. Though N-arylation on azole-bearing analogues has been extensively practised, selective N-arylation either on one N-centre or the exocyclic N-site of the azole ring in competition with other hetero-centres in the framework has been recently explored for azole-carrying systems. Thus, this review would focus on recent advances in chemo- and regio-selective N-arylation (either on one N-centre or the exocyclic N-site of the azole ring) on azole-containing frameworks.

Visible-light-promoted selective O-alkylation of 2-pyridones with α-aryldiazoacetates

A visible-light-promoted O-H insertion reaction between 2-pyridones and α-aryldiazoacetates has been developed. Upon visible light irradiation, the reaction proceeds smoothly under mild and catalyst-free conditions. A wide scope of 2-pyridones and α-aryldiazoacetates are well tolerated, and various O-alkylated 2-pyridones are obtained with perfect selectivity and good functional group tolerance. A photoinduced radical process is probably responsible for the excellent selectivity.