ortho-Induced transition-metal-free C-arylation cyclization reaction for the synthesis of polysubstituted isocoumarins

A new protocol for the synthesis of polysubstituted isocoumarins from 2-iodobenzoic acid and β-diketone compounds has been developed. The occurrence of C-arylation cyclization reaction in transition-metal-free systems and ortho-induced substrates has been exploited. Reactions using these inexpensive conditions have displayed high functional group tolerance and excellent yields.     

Heck reactions of 2-substituted enol ethers with aryl bromides catalysed by a tetraphosphine/palladium complex

cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyses the Heck reaction of β-substituted enol ethers with aryl bromides. Employing β-methoxystyrene, 3-ethoxyacrylonitrile or methyl 3-methoxyacrylate, the regioselective α-arylation of these enol ethers was observed in all cases, and mixtures of Z and E isomers were generally obtained, which in many cases yielded a single ketone product after acid treatment. The stereoselectivity of this reaction depends on steric and electronic factors, and better stereoselectivities in favour of Z isomers were observed with electron-rich or sterically congested aryl bromides. Better yields were obtained for this reaction with electron-rich or sterically congested aryl bromides than with electron-poor aryl bromides. This observation suggests that with these β-substituted enol ethers the rate-limiting step of the catalytic cycle is not the oxidative addition of the aryl bromide to the palladium complex.     

Palladium-catalyzed redox cascade for direct β-arylation of ketones

Herein we report a full article about the detailed design and development of two palladium-catalyzed redox cascade methods that enable direct β-arylation of ketones. Palladium-catalyzed ketone dehydrogenation, aryl-X bond activation and conjugate addition were merged into a redox-neutral catalytic cycle. Non-metal-based aryl electrophiles were used as both the oxidant and the aryl source. The β-arylation with aryl iodides was achieved site-selectively with Pd(TFA)₂/P(i-Pr)₃ as the precatalyst and AgTFA as the iodide scavenger. Both cyclic and linear ketones can react to give β-aryl ketones with excellent functional group tolerance. The β-arylation with diaryliodonium salts was realized without stoichiometric heavy metal additives, and proved to be redox-neutral. A wider substrate scope regarding aryl groups and ketones was obtained for the arylation with diaryliodonium salts, and the possible involvement of palladium nanoparticles as the active catalyst was examined and discussed.     

Recent Progress Concerning the N-Arylation of Indoles

This review summarizes the current state-of-the-art procedures in terms of the preparation of N-arylindoles. After a short introduction, the transition-metal-free procedures available for the N-arylation of indoles are briefly discussed. Then, the nickel-catalyzed and palladium-catalyzed N-arylation of indoles are both discussed. In the next section, copper-catalyzed procedures for the N-arylation of indoles are described. The final section focuses on recent findings in the field of biologically active N-arylindoles.     

Nickel-Catalyzed Amination of (Hetero)aryl Halides Facilitated by a Catalytic Pyridinium Additive

An efficient and operationally simple Ni-catalyzed amination protocol has been developed. This methodology features a simple Ni^II salt, an organic base and catalytic amounts of both a pyridinium additive and Zn metal. A diverse number of (hetero)aryl halides were coupled successfully with primary and secondary alkyl amines, and anilines in good to excellent yields. Similarly, benzophenone imine gave the corresponding N-arylation product in an excellent yield.     

Reactivity of polyhydroxyalkyl-heterocycles towards Lewis acids

We report the reactivity of different polyhydroxyalkyl-heterocycles towards ceric ammonium nitrate (CAN) and ferric chloride. The behaviour of 2-methyl-5-(tetritol-1-yl)-pyrroles and -furans is different towards CAN oxidation. Pyrroles afford 2,5-diformylheterocycles, while furans give access to 1,4-dicarbonyl compounds containing three stereogenic centres. Ferric chloride promotes an intramolecular C-arylation reaction on O-benzylated-polyhydroxyalkyl furans, yielding an isochroman moiety, which is the basic skeleton of a variety of natural products.     

Synthesis and reactivity of chiral pentavalent bismuth derivatives

Eight new pentavalent organobismuth derivatives were synthesized by the reactions of triphenylbismuth or phenyl-2,2"-biphenylenebismuth with chiral (1R)-(–)-camphor-10-sulfonic, (–)-menthyloxyacetic, or (R)-3-phenylbutyric acids. Enantioselective C-arylation of enolizable substrates with organobismuth reagents was carried out for the first time. Unlike iodine, sulfur, and selenium derivatives, which contain a five-membered heterocycle including the 2,2"-biphenylene fragment, phenyl-2,2"-biphenylene organobismuth analogs enter into C-arylation reactions accompanied by the selective transfer exclusively of the phenyl group to the organic substrate.     

A rapid stereoselective C-glycosidation of indoles and pyrrole via indium trichloride promoted reactions of glycosyl halides

Various C-glycosyl indoles and pyrroles were synthesized within a few minutes through coupling acetobromo sugars with suitably substituted indoles and pyrrole in the presence of catalytic amounts of InCl₃ at room temperature. Most of the glycosylations proceeded with a high stereoselectivity.     

Trans-selective γ-arylation of macrocyclic N-picolinoylcycloalkylamines through palladium-catalyzed methylene sp3 carbon–hydrogen bond activation

While numerous stereoselective methylene β- and γ-carbon–hydrogen activation reactions are reported, there are no examples of trans-selective γ-carbon–hydrogen activation of cyclic compounds. Herein I report the first trans-selective palladium-catalyzed γ-arylation of N-picolinoylcycloalkylamine with aryl iodides. Trans-arylation of macrocyclic N-picolinoylcyclododecylamine proceeded to give trans-3-aryl-N-picolinoylcyclododecylamine as a sole mono-arylated product in up to 85% yield. Other, larger substrates were also applicable to trans-arylation, albeit with lower efficiency. The picolinoyl group of the trans-arylated product was easily removed with zinc and diluted hydrochloric acid.     

Development of a scalable palladium-catalyzed α-arylation process for the synthesis of a CGRP antagonist

The Pd-catalyzed α-arylation of cycloheptapyridyl ketone is a key complexity-building step in the synthesis of BMS-846372, a CGRP antagonist. A first-generation process utilized Pd(OAc)₂/P^tBu₃·HBF₄ catalyst system with a strong base NaO^tBu. Although this process was demonstrated on multi-kilo scale, the harsh conditions led to non-selective metal catalyzed processes, which generated several operational, quality, and throughput issues. By acquiring detailed knowledge around several important process parameters, we were able to design an efficient and scalable second-generation α-arylation process using a Pd(OAc)₂/RuPhos catalyst system with the weaker base, K₃PO₄ in tert-amyl alcohol. This new weak base process was high yielding, efficient, and superior in several respects compared to the strong base process. The strategy behind the reaction and isolation development and the process considerations important to scaling a catalytic reaction from laboratory to manufacturing scale will be discussed.     

Palladium(II)-N-heterocyclic carbene-catalyzed direct C2- or C5-arylation of thiazoles with aryl bromides

Herein we report, a series of new benzimidazolium chlorides as N-heterocyclic carbene (NHC) ligand and their corresponding palladium(II)-NHC complexes with the general formula [PdCl₂(NHC)₂] were synthesized. All new compounds were characterized by ¹H NMR, ¹³C NMR, IR spectroscopy and elemental analysis techniques. The catalytic activity of palladium(II)-NHC complexes was investigated in the direct C2- or C5-arylation of thiazoles with aryl bromides in presence of palladium(II)-NHC at 150?°C for 1?h. These complexes exhibited the good catalytic performance for the direct arylation of thiazoles. The arylation of thiazoles regioselectively produced C2- or C5-arylated thiazoles in moderate to high yields.     

Potassium tert-butoxide-mediated generation of arynes from o-bromoacetophenone derivatives

o-bromoacetophenone derivatives as new versatile aryne precursors are induced to selectively eliminate the C_ArBr and C_ArC_(Ac) bonds in the help of t-BuOK. Furthermore, the active aryne intermediates are successfully applied in a substantial set of reactions including N-arylation and copper-catalyzed coupling with various terminal alkynes. It is important to note that the generation of benzyne intermediate is demonstrated through cycloadditon reaction experiment with furan.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

2-Aminophenones,a common precursor to N-aryl isatins and acridines endowed with bioactivities

Because N-arylation of isatin only worked with iodoferrocene (and in low yield), we employed N-arylation of 2-aminophenones and subsequent oxidative cyclization to access various N-arylated isatins. In the course of this work, we observed that N-arylation using 2-iodofuran, 2-iodobenzofuran and 2-iodobenzothiophene did not lead to the expected derivatives, but to (benzo)furo- and (benzo)thieno[2,3-b]quinolines. Separate cyclization was also performed under acidic conditions on 2-(arylamino)phenones in order to obtain acridines and related compounds. Most of the synthesized compounds were screened for their antiproliferative activity in A2058 melanoma cells, and against a panel of disease-relevant kinases such as mammalian CDK5/p25, PIM1, CLK1, DYRK1A, GSK3α/β, Haspin and leishmanial CK1. The biological results are reported.     

CuI catalyst heterogenized on melamine-pyridines immobilized SBA-15: Heterogeneous and recyclable nanocatalyst for Ullmann-type CN coupling reactions

The present study reports the procedure conducted in SBA-15/CCPy/CuI preparation as a new Mesoporous nanocatalyst, whereas melamine bearing pyridine groups on SBA-15 are used to secure CuI catalyst as capping agent. The resultant catalyst was specified by conducting TEM, FESEM, WDX, ICP, and EDS. The SBA-15/CCPy/CuI catalytic behavior was studied to N-arylation of indole, imidazole, pyrazole, benzyl amine, and aniline by coupling reactions of Ullmann-type CN. Also, the heterogeneous catalyst may simply be recovered via filtration and used again for seven cycles with no considerable loss in activity. The findings revealed the privileges of the present method, including the high product yield, experimental simplicity, low catalyst loading, broad substrate scope, and short reaction times.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

C4-arylation and domino C4-arylation/3,2-carbonyl migration of indoles by tuning Pd catalytic modes: Pd(i)–Pd(ii) catalysis vs. Pd(ii) catalysis

Efficient C4-arylation and domino C4-arylation/3,2-carbonyl migration of indoles have been developed. The former route enables C4-arylation in a highly efficient and mild manner and the latter route provides an alternative straightforward protocol for synthesis of C2/C4 disubstituted indoles. The mechanism studies imply that the different reaction pathways were tuned by the distinct acid additives, which led to either the Pd(i)–Pd(ii) pathway or Pd(ii) catalysis.

C4-arylation via Pd(i)–Pd(ii) catalysis and domino C4-arylation/3,2-carbonyl migration of indoles via Pd(ii) catalysis tuning by acids have been developed.     

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

It was determined that diaryliodonium(III) triflates bearing a trimethoxybenzene (TMP) auxiliary are more reactive than the reported selective aryl-transfer iodonium salts in the N-arylation of benzimidazoles and other types of azole compounds under catalytic conditions. The TMP-iodonium(III) salts can thus effectively facilitate the reaction at 50?°C or below, producing the corresponding N-arylated biaryls without the formation of TMP-derived coupling byproducts. Utilization of this TMP reagent under mild conditions would prevent the underlying problem of participation of the auxiliary group in the coupling reactions, which is observed while using the iodonium(III) salts that require elevated temperatures.     

Chan-Lam cross-coupling reaction based on the Cu2S/TMEDA system

A catalyst based on the readily available Cu₂S/TMEDA system using a stable copper(I) source was developed for the Chan-Lam cross-coupling reaction. The capability of the catalyst was demonstrated with 1H-benzo[d]imidazol-2(3H)-one, 1H-benzo[d]imidazole, and 1H-imidazole together with electron-deficient, electron-rich, and sterically demanding boronic acids at room temperature in the presence of atmospheric oxygen to give the cross-coupling products in moderate to excellent yields. In addition, the coupling reaction of 1H-benzo[d]imidazole with several pinacol or neopentylglycol boronates indicated further potential of the catalyst. The reaction conditions tolerate the hydroxyl and bromo functional groups. The catalytic system also enables to synthesize the mono-N-substituted anilines from primary aliphatic amines. However, the two model compounds for the secondary and aromatic amines, piperidine and aniline, do not react. Two sterically demanding products with the restricted CN bond rotation, synthesized by the N-arylation of 1H-benzo[d]imidazol-2(3H)-one with o-tolylboronic acid, enabled to confirm the atropisomers prepared by the Chan-Lam cross-coupling reaction. Furthermore, an example of one-pot Chan-Lam and Suzuki-Miyaura reaction has been reported.     

Chiral Primary Amine Catalyzed α-Arylation of Simple Ketones via Asymmetric Retro-Claisen Cleavage

Highly enantioselective α-arylation of simple ketones has been achieved by chiral primary amine catalyzed asymmetric retro-Claisen cleavage of β-diketones. This mild organocatalytic strategy enables the construction of α-aryl tertiary carbon stereocenters in good yields and excellent enantioselectivities (up to 98 % ee) with the para-quinone monoimines as aryl sources. Furthermore, oxidative catalytic asymmetric α-arylation has also been realized with free p-aminophenols.