Efficient N-arylation of azole compounds utilizing selective aryl-transfer TMP-iodonium(III) reagents

Copper-catalyzed N-arylation of 1,2,4-oxadiazin-5(6H)-ones by diaryliodonium salts

Herein, we developed a new synthetic approach for the preparation of N-arylated 1,2,4-oxadiazin-5(6H)-ones by direct arylation with diaryliodonium salts. The reaction with symmetrical diaryliodonium salts using CuI as a catalyst proceeded in toluene in the presence of DIPEA at 60 °C with the formation of the desired products in isolated yields of 46 to 97% (20 examples). The use of more readily available unsymmetrical diaryliodonium salts required higher reaction temperatures (up to 100 °C) to achieve similar yields. The only limitation observed in reaction was with an ortho-substituted iodonium salt. In all other cases, the developed approach allowed the preparation of a broad range of N-arylated 1,2,4-oxadiazin-5(6H)-ones under mild conditions utilizing a cheap and readily available catalyst.

Silver-Catalyzed Coupling of Unreactive Carboxylates: Synthesis of α-Fluorinated O-Aryl Esters

α-Fluorinated aryl esters pose a challenge in synthesis via O-arylation of α-fluorinated carboxylates owing to their low reactivities. This limitation has been addressed by combining a silver catalyst with aryl(trimethoxyphenyl)iodonium tosylates to access α-fluorinated aryl esters. We envision that the catalytic system involves high-valent aryl silver species generated via the oxidation of silver(I) salt. The present method provided a synthetic protocol for various α-fluorinated aryl esters including fluorinated analogs of drug derivatives.

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.

Ligand-free Ullmann-type arylation of oxazolidinones by diaryliodonium salts

The arylation of azaheterocycles can be considered as one of the most important processes for the preparation of various biologically active compounds. In the present work, we describe a method for the copper-catalyzed N-arylation of hindered oxazolidinones using diaryliodonium salts. The method succeeds in good to excellent yields for the arylation of 4-alkyloxazolidinones, including sterically hindered isopropyl- and tert-butyl-substituted. The efficiency of the method was demonstrated for a wide range of diaryliodonium salts - symmetric and unsymmetric as well as ortho-substituted derivatives. The developed approach will provide an important contribution in the development and preparation of novel drugs and bioactive molecules containing oxazolidinone moieties.

13C-NMR Chemical Shifts in 1,3-Benzazoles as a Tautomeric Ratio Criterion

Benzimidazole is an important heterocyclic fragment, present in many biologically active compounds with a great variety of therapeutic purposes. Most of the benzimidazole activities are explained through the existence of 1,3-tautomeric equilibrium. As the binding affinity of each tautomer to a protein target depends on an established bioactive conformation, the effect of tautomers on the ligand protein binding mechanism is determinant. In this work, we searched and analyzed a series of reported ¹³C-NMR spectra of benzazoles and benzazolidine-2-thiones with the purpose of estimating their tautomeric equilibrium. Herein, several approaches to determine this problem are presented, which makes it a good initial introduction to the non-expert reader. This chemical shift difference and C4/C7 signals of benzimidazolidine-2-thione and 1-methyl-2-thiomethylbenzimidazole as references were used in this work to quantitatively calculate, in solution, the pyrrole–pyridine tautomeric ratio in equilibrium. The analysis will help researchers to correctly assign the chemical shifts of benzimidazoles and to calculate their intracyclic or exocyclic tautomeric ratio as well as mesomeric proportion in benzimidazoles.

An Unexpected Reaction between Diaryliodonium Salts and DMSO

Diaryliodonium salts are useful arylating reagents that have been exploited widely. In this Communication, we demonstrate that heating diphenyliodonium triflate in the solvent DMSO leads to an unexpected arylation reaction. It is postulated that arylation of DMSO at oxygen, followed by a thia-Sommelet–Hauser rearrangement, leads to the formation of 2-thiomethylphenols. More substituted diaryliodonium salts and cyclic diaryliodonium salts are shown to be more stable and less likely to react with DMSO. In conclusion, when using iodonium salts dissolved in DMSO, beware of side-reactions.

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.

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.

Aryl(TMP)iodonium Tosylate Reagents as a Strategic Entry Point to Diverse Aryl Intermediates: Selective Access to Arynes

Arenes are broadly found motifs in societally important molecules. Access to diverse arene chemical space is critically important, and the ability to do so from common reagents is highly desirable. Aryl(TMP)iodonium tosylates provide one such access point to arene chemical space via diverse aryl intermediates. Here we demonstrate that controlling reaction pathways selectively leads to arynes with a broad scope of arenes and arynophiles (24 examples, 70% average yield) and efficient access to biologically active compounds.

The selective synthesis of N-arylbenzene-1,2-diamines or 1-arylbenzimidazoles by irradiating 4-methoxy-4'-substituted-azobenzenes in different solvents

The solvent-controllable photoreaction of 4-methoxyazobenzenes to afford 1-aryl-1H-benzimidazoles or N-arylbenzene-1,2-diamines has been studied. The irradiation of 4-methoxyazobenzenes in DMF containing 0.5 M hydrochloric acid provided N²-aryl-4-methoxybenzene-1,2-diamines as the major product, while irradiation in acetal containing 0.16 M hydrochloric acid led to 1-aryl-6-methoxy-2-methyl-1H-benzimidazoles as the major product. A possible reaction mechanism explaining the selectivity was also discussed.

A solvent-controllable photoreaction involving 4-methoxyazobenzenes has been developed to synthesize 1-aryl-1H-benzimidazoles or N-arylbenzene-1,2-diamines in moderate to good yields.

Diaryliodoniums Salts as Coupling Partners for Transition-Metal Catalyzed C- and N-Arylation of Heteroarenes

Owing to the pioneering works performed on the metal-catalyzed sp2 C–H arylation of indole and pyrrole by Sanford and Gaunt, N– and C-arylation involving diaryliodonium salts offers an attractive complementary strategy for the late-stage diversification of heteroarenes. The main feature of this expanding methodology is the selective incorporation of structural diversity into complex molecules which usually have several C–H bonds and/or N–H bonds with high tolerance to functional groups and under mild conditions. This review summarizes the main recent achievements reported in transition-metal-catalyzed N– and/or C–H arylation of heteroarenes using acyclic diaryliodonium salts as coupling partners.

Cu(i) based catalysts derived from bidentate ligands and studies on the effect of substituents for N-arylation of benzimidazoles and indoles

Four Cu(i) complexes [Cu(L^1–4)(Cl)(PPh₃)] (C1–C4) were synthesized, characterized and crystal structure of C1 was determined. Complexes were utilized as catalysts for N-arylation reaction. Probable mechanism for N-arylation reaction was proposed.

High-performance sono/nano-catalytic system: CTSN/Fe3O4-Cu nanocomposite, a promising heterogeneous catalyst for the synthesis of N-arylimidazoles

Herein, a promising heterogeneous nanoscale catalytic system constructed of chitosan (CTSN, as a polymeric basis), iron oxide nanoparticles (Fe3O4 NPs, as the magnetic agent), and copper oxide nanoparticles (CuO NPs, as the main catalytic active site) is presented. Firstly, a convenient synthetic route for preparation of this novel nanocatalyst (CTSN/Fe3O4-Cu) is presented. Further, the synergistic catalytic effect between the novel-designed catalyst and ultrasound waves (USW) in N-arylation coupling reactions of the imidazole derivatives (using various aryl halides) is precisely discussed. Concisely, high reaction yields (98%) have been obtained in short reaction time (10 min) through applying a partial amount (0.01 g) of this nanocatalyst. As the main reason for high catalytic activity of CTSN/Fe3O4-Cu, nanosized cluster-shaped morphology, which provides a wide surface active area, can be expressed. However, as the most distinguished properties of CTSN/Fe3O4-Cu catalytic system, high convenience in separation and excellent reusability could be mentioned. CTSN/Fe3O4-Cu nanocomposite can be easily recovered by using an external magnet and reused at least for eight times with no significant decline in the catalytic activity. Structural characterizations of this novel system have been done by various analytical methods and the obtained results have been well interpreted in the context.

Domino N-/C- or N-/N-/C-arylation of imidazoles to yield polyaryl imidazolium salts via atom-economical use of diaryliodonium salts

Herein, we disclose a Cu-mediated domino di-/triarylation reaction of imidazoles to efficiently access polyaryl imidazolium salts in a single step by using two aryls as well as an anion of a diaryliodonium salt. The diarylation shows high atom economy and excellent selectivity with unsymmetrical iodonium salts.

Dataset on synthesis and crystallographic structure of phenyl(TMP)iodonium(III) acetate

The data in this article are related to research article ‘‘Efficient N-arylation of azole compounds utilizing selective aryl-transfer TMP-iodonium (III) reagents (Koseki et al., 2019). For the title compound, phenyl(2,4,6-trimethoxyphenyl)iodonium(III) acetate (Ph(TMP)IOAc), the single-crystal X-ray diffraction measurement together with NMR analysis, like also the method of synthesis and crystallization are presented. The X-ray structure analysis has revealed that the two types of geometries regarding the acetate anion attached to phenyl (TMP)iodonium (III) cation are found in the crystal states.