A simple access to triarylmethane derivatives from aromatic aldehydes and electron-rich arenes catalyzed by FeCl3

Generation of C(sp3)-CAr bonds in the synthesis of triarylmethanes (TRAMs): comprehensive progress since 2009

Triarylmethanes are useful compounds in materials science and medicinal chemistry. These moieties are important constituents of dyes and pharmaceuticals. These scaffolds are synthesized either by Friedel-Crafts alkylation of aldehydes and arenes or by the functionalization of diarylmethanes. The development of effective catalytic systems and the discovery of highly regio- and stereoselective methods using Brønsted or Lewis acid catalysts represent particularly important achievements in this field. This review explores the detailed documentation of the various catalytic strategies witnessed since 2009 for the synthesis of triarylmethanes, which could arouse the interest of readers in organic synthesis.

HFIP-Mediated Dual C(Ar)-Alkylation Process Towards the Regioselective Synthesis of Triarylmethanes (TRAMs)

The distinct roles of different chemical species are essential for the discovery of novel chemical transformations in organic synthesis. Here, we have designed a potential strategy for the synthesis of triarylmethanes (TRAMs) using the dual C(aryl)-alkylation process. This protocol was influenced by 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as a pivotal reagent and proceeds through the selective para C-H functionalization method. The described approach has been proven to be highly efficient in terms of substrate scope with excellent functional group tolerance and gram scale synthesis of the desired product with 90 % yield. The recyclability and reusability of HFIP has enhanced the feasibility of this protocol towards the sustainable synthesis of TRAMs.

Synthesis of fluorenes and their related compounds from biaryls and Meldrum's acid derivatives

A new synthetic method for preparing fluorenes from amino group-containing biaryls and Meldrum's acid derivatives was developed. The reaction proceeded without a catalyst and loss of functional groups. The corresponding six- and seven-membered cyclic products were obtained using biaryl ether and ortho-terphenyl as substrates, respectively.

Metal- and solvent-free synthesis of aniline- and phenol-based triarylmethanes via Brönsted acidic ionic liquid catalyzed Friedel-Crafts reaction

A beneficial, scalable and efficient methodology for the synthesis of aniline-based triarylmethanes has been established through the double Friedel-Crafts reaction of commercial aldehydes and primary, secondary or tertiary anilines using Brönsted acidic ionic liquid as a powerful catalyst, namely [bsmim][NTf2]. This protocol was successfully performed under metal- and solvent-free conditions with a broad range of substrates, giving the corresponding aniline-based triarylmethane products in good to excellent yields (up to 99%). In addition, alternative aromatic nucleophiles such as phenols and electron-rich arenes were also studied using this useful approach to achieve a diversity of triarylmethane derivatives in high to excellent yields.

Selective Synthesis of Acylated Cross-Benzoins from Acylals and Aldehydes via N-Heterocyclic Carbene Catalysis

The utility of acylals as building blocks for selective cross-benzoin synthesis was explored in this study. The synthesis of α-acetoxyketones (O-acyl cross-benzoins) was achieved via selective N-heterocyclic carbene-catalyzed cross-benzoin reactions using acylals as aldehyde equivalents. Thus, the combination of ortho-substituted phenyl acylals and aromatic/aliphatic aldehydes as coupling substrates using bicyclic triazolium salts as precatalysts and potassium carbonate as a base in THF at reflux temperature selectively yielded O-acyl cross-benzoins.

Transition-Metal-Free Synthesis of Polyfunctional Triarylmethanes and 1,1-Diarylalkanes by Sequential Cross-Coupling of Benzal Diacetates with Organozinc Reagents

A variety of functionalized triarylmethane and 1,1-diarylalkane derivatives were prepared via a transition-metal-free, one-pot and two-step procedure, involving the reaction of various benzal diacetates with organozinc reagents. A sequential cross-coupling is enabled by changing the solvent from THF to toluene, and a two-step SN 1-type mechanism was proposed and evidenced by experimental studies. The synthetic utility of the method is further demonstrated by the synthesis of several biologically relevant molecules, such as an anti-tuberculosis agent, an anti-breast cancer agent, a precursor of a sphingosine-1-phosphate (S1P) receptor modulator, and a FLAP inhibitor.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

A facile iron-catalyzed dual C–C bond cleavage: an approach towards triarylmethanes

An efficient iron-catalyzed dual C–C bond cleaving reaction has been developed for the synthesis of triarylmethanes.

Synthesis of new mixed-bistriarylmethanes and novel 3,4-dihydropyrimidin-2(1H)one derivatives

Formylated-triarylmethanes were realized as ideal precursors for the design and synthesis of mixed-bistriarylmethanes and 3,4-dihydropyrimidin-2(1H)one-triarylmethane hybrid derivatives.

Detection of therapeutic radiation in three-dimensions

For over the last twenty years there has been a multitude of sophisticated three-dimensional radiation delivery procedures developed which requires a corresponding verification of the impact on patients. This article reviews the state of the art in the development of chemical detectors used to characterize the three-dimensional shape of therapeutic radiation. These detectors are composed of polyurethane, radical initiator and a leuco dye, which is radiolytically oxidized to a dye absorbing at 630 nm.

Additional synthesis on thiophene-containing trisubstituted methanes (TRSMs) as inhibitors of M. tuberculosis and 3D-QSAR studies

We earlier reported thiophene-containing trisubstituted methanes (TRSMs) as novel cores carrying anti-tubercular activity, and identified S006-830 as the phenotypic lead with potent bactericidal activity against single- and multi-drug resistant clinical isolates of Mycobacterium tuberculosis (M. tb). In this work, we carried out additional synthesis of several TRSMs. The reaction scheme essentially followed the Grignard reaction and Friedel-Crafts alkylation, followed by insertion of a dialkylaminoethyl chain. We also performed microbiological evaluations including in vitro screening against the virulent strain M. tb H37Rv, cytotoxicity assessment in the Vero C-1008 cell line, and 3D-QSAR studies with comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA). CoMFA and CoMSIA models yielded good statistical results in terms of q² and r² values, suggesting the validity of the models. It was concluded that a para-substituted benzene ring with bulkier electron-donating groups and aminoalkyl chains are required for higher inhibitory capacity against M. tuberculosis. We believe that these insights will rationally guide the design of newer, optimal, TRSMs.

Copper-mediated arylation with arylboronic acids: Facile and modular synthesis of triarylmethanes

A facile and modular synthesis of triarylmethanes was achieved in good yield via a two-step sequence in which the final step is the copper(II)-catalyzed arylation of diarylmethanols with arylboronic acids. By using this protocol a variety of symmetrical and unsymmetrical triarylmethanes were synthesized. As an application of the newly developed methodology, we demonstrate a high-yielding synthesis of the triarylmethane intermediate towards an anti-breast-cancer drug candidate.

Facile synthesis of nonsymmetrical heteroaryl-substituted triarylmethanes via the FeCl3·6H2O-catalyzed two-step Friedel–Crafts-type reaction

A mild, facile, atom economical and efficient method was described for the synthesis of functionalized nonsymmetrical heteroaryl-substituted triarylmethanes via the two step Friedel–Crafts-type reaction catalyzed by FeCl₃·6H₂O under “open-flask” at room temperature.

Nickel-Catalyzed Arylation of Heteroaryl-containing Diarylmethanes: Exceptional Reactivity of the Ni(NIXANTPHOS)-based Catalyst

Nickel(0)-catalyzed cross-coupling of heteroaryl-containing diarylmethanes with both aryl bromides and chlorides has been achieved. The success of this reaction relies on the introduction of a unique nickel/NIXANTPHOS-based catalyst system, which provides a direct route to triarylmethanes from heteroaryl-containing diarylmethanes. Reactivity studies indicate the Ni(NIXANTPHOS)-based catalyst exhibits enhanced reactivity over XANTPHOS derivatives and other Ni(phosphine)-based catalysts in the reactions examined.

Microwave-assisted synthesis of 6,6′-(aryl(alkyl)methylene)bis(2,4-dialkylphenol) antioxidants catalyzed by multi-sulfonated reduced graphene oxide nanosheets in water

Sulfonated reduced graphene oxide nanosheets were characterized and employed in the synthesis of bisphenolic antioxidants in water under microwave conditions.

The cooperative effect of Lewis pairs in the Friedel–Crafts hydroxyalkylation reaction: a simple and effective route for the synthesis of (±)-carbinoxamine

Lewis acid (with or without a Lewis base) enhances the electrophilicity of aldehydes to react with aromatic π-nucleophiles and generate carbinols.

Highly sulfonated graphene and graphene oxide nanosheets as heterogeneous nanocatalysts in green synthesis of bisphenolic antioxidants under solvent free conditions

Sulfonated functionalized graphene and graphene oxide nanosheets were prepared via chemical approaches and their catalytic activities were investigated in the green synthesis of 6,6′-(arylmethylene)bis(2,4-dialkylphenol) antioxidants.

Regiospecific, one-pot, and pseudo-five-component synthesis of 6,6′-(arylmethylene)bis(2-(tert-butyl)4-methylphenol) antioxidants using highly sulfonated multi-walled carbon nanotubes under solvent-free conditions

This is the first report of an innovative, one-pot, pseudo-five-component, and solvent-free synthesis of 6,6′-(arylmethylene)bis(2-(tert-butyl)4-methylphenol) antioxidants from p-cresol, methyl tert-butyl ether, and aldehydes in the presence of sulfonated multi-walled carbon nanotubes (MWCNTs-SO3H) as heterogeneous, robust, and reusable catalysts under solvent-free conditions. MWCNTs-SO3H was prepared and characterized by some microscopic and spectroscopic techniques including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, dispersibility in different solvent, and thermogravimetric analysis (one functionality every approximately five carbon atoms). The acidity of the catalyst was measured by acid–base titration (1.80 mmol g−1). This reaction proceeds smoothly to give the products in good yields. The catalyst was reused several times without efficient loss of its activity for the preparation of 6,6′-(arylmethylene)bis(2-(tert-butyl)4-methylphenol) antioxidants. In addition, high yields of the products and solvent-free and nontoxicity of the catalyst are other worthwhile advantages of the present method.

Synthesis and X-ray crystal structure of isomeric pyridine-based leuco-TAM dyes, 2,2-(2-(pyridinyl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimethyl indoline) derivatives and unusual stability of 4-pyridinyl compound

The solid-state structures and unequivocal stereochemistries of isomeric pyridine-based leuco-triarylmethane (LTAM) dyes 2,2'-(2-(pyridin-4 or 3-yl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimethylindoline) derivatives were established by X-ray crystallography. Surprisingly, the EE isomer was formed for the 4-pyridinyl compound, whereas the 3-pyridinyl compound formed ZE isomers. In addition, the latter have a so-called three-bladed propeller conformation, whereas the former possess a Y-shaped conformation. These pyridine-based LTAM compounds stack to form a dimer, adopting either an orthorhombic, with Pcmn space group, or monoclinic crystal system with P21/n space group in the crystal unit cell.

Palladium-catalyzed diarylmethyl C(sp3)-C(sp2) bond formation: a new coupling approach toward triarylmethanes

Palladium-catalyzed reductive coupling reactions between N-tosylhydrazones and aryl halides lead to the formation of C(sp(3))-C(sp(2)) bonds. This approach provides a general route for the synthesis of triarylmethanes.

Palladium-catalyzed C(sp3)-H arylation of diarylmethanes at room temperature: synthesis of triarylmethanes via deprotonative-cross-coupling processes

Although metal-catalyzed direct arylation reactions of non- or weakly acidic C-H bonds have recently received much attention, chemists have relied heavily on substrates with appropriately placed directing groups to steer reactivity. To date, examples of intermolecular arylation of unactivated C(sp(3))-H bonds in the absence of a directing group remain scarce. We report herein the first general, high-yielding, and scalable method for palladium-catalyzed C(sp(3))-H arylation of simple diarylmethane derivatives with aryl bromides at room temperature. This method facilitates access to a variety of sterically and electronically diverse hetero- and nonheteroaryl-containing triarylmethanes, a class of compounds with various applications and interesting biological activity. Key to the success of this approach is an in situ metalation of the substrate via C-H deprotonation under catalytic cross-coupling conditions, which is referred to as a deprotonative-cross-coupling process (DCCP). Base and catalyst identification were performed by high-throughput experimentation (HTE) and led to a unique base/catalyst combination [KN(SiMe(3))(2)/Pd-NiXantphos] that proved to efficiently promote the room-temperature DCCP of diarylmethanes. Additionally, the DCCP exhibits remarkable chemoselectivity in the presence of substrates that are known to undergo O-, N-, enolate-, and C(sp(2))-H arylation.

SbCl(3)-catalyzed one-pot synthesis of 4,4'-diaminotriarylmethanes under solvent-free conditions: Synthesis, characterization, and DFT studies

A simple, efficient, and mild procedure for a solvent-free one-step synthesis of various 4,4'-diaminotriarylmethane derivatives in the presence of antimony trichloride as catalyst is described. Triarylmethane derivatives were prepared in good to excellent yields and characterized by elemental analysis, FTIR, (1)H and (13)C NMR spectroscopic techniques. The structural and vibrational analysis were investigated by performing theoretical calculations at the HF and DFT levels of theory by standard 6-31G*, 6-31G*/B3LYP, and B3LYP/cc-pVDZ methods and good agreement was obtained between experimental and theoretical results.

Friedel-Crafts arylation reactions of N-sulfonyl aldimines or sulfonamidesulfones with electron-rich arenes catalyzed by FeCl3 x 6 H2O: synthesis of triarylmethanes and bis-heteroarylarylmethanes

The FeCl(3) x 6H(2)O-catalyzed Friedel-Crafts arylation reactions of N-sulfonyl aldimines or sulfonamidesulfones with electron-rich arenes and heteroarenes, which lead to the formation of triarylmethanes and bis-heteroarylarylmethanes, are developed. The use of mild reaction conditions, low catalytic loading, high yield, and single step synthesis are the advantages of the present procedure.