Pd(II)-catalyzed synthesis of indoles from α-aryloxime O-pentafluorobenzoates via intramolecular aromatic C-H amination

α-Aryl-α-aminocarbonyloxime O-pentafluorobenzoates are found to be promising precursors for synthesis of 2,3-disubstituted indole derivatives catalyzed by PdCl₂(MeCN)₂ in the presence of MgO as a base. The reaction is supposed to proceed via intramolecular aromatic C-H amination of a vinyl nitrene-palladium intermediate.     

Cu(II)-catalyzed acetoxylation of arenes by 1,2,3-triazole-directed C–H activation

A facile and efficient method for the regioselective acetoxylation of 1-benzyl 1,2,3-triazoles through C–H bond activation was developed. Cu(OAc)₂ and 1,2,3-triazole were applied as catalyst and elegant directing group, respectively, to convert aromatic C–H bonds directly into highly regioselective C–O bonds. The conversion can result in the synthesis of 1,2,3-triazoles bearing acetoxyl groups.     

Recent advances in Palladium(II)-catalyzed activation of aromatic ring C–H bonds

Palladium is a precious metal, which has been widely used for various organic transformations in the past decades. Currently, the palladium-catalyzed direct activation of the aromatic ring C–H bonds is one of the frontier areas in organic chemistry, and the progress of research in this field is very rapid. Compared with other transition metals, palladium has the advantages of high catalytic activity and strong selectivity. Combining the domestic and foreign scholars' research on this aspect, this paper summarizes the research progress of the palladium-catalyzed activation of aromatic ring C–H bonds in the past ten years.     

Synthesis of indenoquinolinone through aryne-mediated Pd(II)-catalysed remote C–H activation

Research on Chemical Intermediates - Indenoquinolinones have been synthesized from 2-haloquinoline-3-carbaldehyde through Pd-mediated simultaneous C–H (aldehyde) and C–X bond...     

Palladium(II)-catalyzed oxidative annulation of alkenylindoles with alkynes initiated by C–H activation

A palladium(II)-catalyzed annulation of alkenylindoles with diarylethynes initiated by C–H bond activation was developed. This method provided a convenient way for the synthesis of dihydrocyclopenta[b]indoles by enyne cyclization initiated by C–H bond activation.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Monoligated Pd(0)-catalyzed intramolecular ortho- and para-arylation of phenols for the synthesis of aporphine alkaloids. Synthesis of (−)-lirinine

An intramolecular palladium(0)-mediated ortho-arylation of phenols applied to the synthesis of various substituted aporphines is reported. Most significantly, the efficiency of the transformation was enhanced by the use of monoligated Pd(0) complexes. This methodology was extended to para-arylation of phenols and employed in the synthesis of the aporphine alkaloid (?)-lirinine.     

Pd(II)-catalyzed cascade Heck/intramolecular C(sp2)–H amidation reaction: An efficient route to 4-aryl-2-quinolinones

A Pd(II)-catalyzed cascade Heck/intramolecular C(sp²)–H amidation reaction is described for the synthesis of 4-aryl-2-quinolinone derivatives. Substituted cinnamamide containing 2-(pyridin-2-yl)ethanamine unit reacts with aryl iodide to form intermediate by Heck reaction. Then, the intermediate takes place intramolecular amidation via C(sp²)–H activated process promoted by orientation group.     

Asymmetric intramolecular C–H insertion of sulfonyldiazoacetates catalyzed by Rh(II)

The asymmetric C–H insertion of alkyldiazosulfones has been studied. High selectivity was achieved using a combination of a chiral catalyst and a chiral auxiliary (Rh₂(S-pttl)₄ and menthyl ester).     

Regioselective copper(I)-catalyzed C–H hydroxylation/C–S coupling: expedient construction of 2-(styrylthio)phenols

Regioselective copper(I)-catalyzed C–H hydroxylation/C–S coupling of aryl thiols with vinyl halides was developed. Starting from substituted aryl thiols and vinyl halides, various 2-(styrylthio)phenol derivatives were efficiently prepared. The application of the synthetic methodology to generate the bioactive organic intermediate was also exemplified.     

Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

Ruthenium(II)-catalyzed C(3)–H arylation of furan moiety in fuberidazole derivatives

An efficient selective C(3)–H arylation of furan ring in 2-(furan-2-yl)benzimidazoles, derivatives of fuberidazole fungicide, with aryl bromides catalyzed by [RuCl₂(cymene)]₂/ pivalic acid system has been accomplished. High selectivity of the process may be accounted for by the action of benzimidazol-2-yl substituent as the directing group.     

Direct synthesis of benzoxazinones via Cp*Co(III)-catalyzed C–H activation and annulation of sulfoxonium ylides with dioxazolones

A highly novel and direct synthesis of benzoxazinones was developed via Cp*Co(III)-catalyzed C–H activation and [3 + 3] annulation between sulfoxonium ylides and dioxazolones. The reaction is conducted under base-free conditions and tolerates various functional groups. Starting from diverse readily available sulfoxonium ylides and dioxazolones, a variety of benzoxazinones could be synthesized in one step in 32%-75% yields.     

Development of the radical C–O coupling reaction of phenols toward the synthesis of natural products comprising a diaryl ether skeleton

Compounds comprising a diaryl ether skeleton exist among natural phenols. The diaryl ether skeleton is thought to be biosynthesized through the coupling of two or more phenols. It is an important structural feature in medicines and agrochemicals, and it is imperative to develop methods for constructing such skeletons in organic synthesis. However, by the synthesis method through the coupling of phenols, coupling occurs preferentially at the ortho-substituted carbon atom of phenols. In this study, various radical-generating reagents and conditions were investigated with the aim of developing a short-step construction method of the diaryl ether skeleton by the radical homo-coupling of two phenol molecules. In addition, cross-coupling reactions between radicals of 2,4,6-tri-tert-butylphenol and p-substituted phenol were conducted to synthesize eight C (ortho)–O coupling products. Based on the results, a computational chemical approach was employed to verify the cause of C (ortho)–O bond formation.     

Highly effective activation of aryl chlorides for Suzuki coupling in aqueous media using a ferrocene-based Pd(II)–diimine catalyst

The Suzuki coupling of aryl chlorides with boronic acids using a ferrocene-containing Pd(II)–diimine complex as catalyst, in aqueous media, under microwave heating is reported. A small amount of the catalyst (0.1%) was found to be highly effective for coupling unactivated aryl chlorides with boronic acids to form sterically hindered ortho-substituted biaryls. The same catalyst also enabled the coupling of aryl bromides and iodides with various boronic acids in very high yields. The catalyst is air stable and the catalytic reaction can be completed in 15 min.     

Cp*Co(III) catalyzed annulation of N-Cbz hydrazones for the redox-neutral synthesis of isoquinolines via C–H/N–N bond activation

Abstract

A new cascade oxidative cyclization reaction of N-Cbz hydrazones with internal alkynes has been explored for the preparation of isoquinoline derivatives using Cp*Co^III-catalyst through C–H and N–N bond functionalization. N-Cbz hydrazones are rarely explored as directing group for redox-neutral [4?+?2] cyclization reaction through the cyclometallation and this catalyst system does not require any external oxidizing agent, as well as, silver or antimony salt. The current efficient approach has been utilized for the synthesis of different isoquinoline derivatives with good regioselectivity and yields.     

Pd(II)-Mediated C−H Activation for Cysteine Bioconjugation

Selective bioconjugation remains a significant challenge for the synthetic chemist due to the stringent reaction conditions required by biomolecules coupled with their high degree of functionality. The current trailblazer of transition-metal mediated bioconjugation chemistry involves the use of Pd(II) complexes prepared via an oxidative addition process. Herein, the preparation of Pd(II) complexes for cysteine bioconjugation via a facile C−H activation process is reported. These complexes show bioconjugation efficiency competitive with what is seen in the current literature, with a user-friendly synthesis, common Pd(II) sources, and a more cost-effective ligand. Furthermore, these complexes need not be isolated, and still achieve high conversion efficiency and selectivity of a model peptide. These complexes also demonstrate the ability to selectively arylate a single surface cysteine residue on a model protein substrate, further demonstrating their utility.     

Cobalt (II)-catalyzed direct C3-selective C–H acyloxylation of indoles with tert-butyl peresters

A Co(II)-catalyzed direct C3-selective C–H acyloxylation of indoles has been realized with tert-butyl peresters serving as both an acyloxy source and an oxidant. This reaction features highly C3 regioselectivity and good functional group tolerance, which provides a convenient and versatile approach to the construction of valuable 3-acyloxyindoles in moderate to excellent yields.     

Enantioselective synthesis of β-lactams via the IndaBox-Cu(II)-catalyzed Kinugasa reaction

The enantioselective Kinugasa reaction of nitrones with terminal alkynes in the presence of 20 mol % of IndaBox-Cu(OTf)₂ and di-sec-butylamine (1.5 equiv) produced β-lactams with the highest level of enantiomeric excesses among the catalytic enantioselective Kinugasa reactions reported so far.     

Intramolecular Diels–Alder reaction for the synthesis of tetracyclic carbazoles and isocanthines

One pot intramolecular Diels–Alder reaction has been efficiently used as a new route for the synthesis of four tetracyclic carbazoles and four isocanthine analogues where a dialdehyde is utilised as a common intermediate for both the scaffolds. Biological activity was evaluated for some molecules, which demonstrated moderate activity against HeLa cervical cancer cell lines.