Iodine-catalyzed Friedel–Crafts alkylation of electron-rich arenes with aldehydes: efficient synthesis of triarylmethanes and diarylalkanes

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.

I2-Promoted Chemoselective Annulative Coupling of 2-Aminobenzamides with Sulfoxonium Ylides: Easy Access to Quinazolinones

A flexible and metal-free synthetic approach for synthesizing 2-benzoyl quinazolinones and 2-aryl quinazolinones via molecular iodine-mediated annulative coupling of sulfoxonium ylides with 2-aminobenzamides has been disclosed. The method demonstrates remarkable chemoselectivity and efficiency, leading to high yields of 2-benzoyl quinazolinones and 2-aryl quinazolinones under optimized conditions. The broad substrate scope, scalability, and practical utility were highlighted through diverse applications, including gram-scale reactions and the synthesis of biologically significant compounds such as tryptanthrin and the chemo/biosensor derivative.

Gram-Scale Synthesis of Substituted Triarylmethanes

In this paper, a high-yield, open-vessel route for the facile-operational, gram-scale synthesis of functionalized triarylmethanes (TRAMs) is described via silica coated magnetic nanoparticles of modified polyphosphoric acid (NiFe2O4@SiO2-PPA)-mediated intermolecular Friedel-Crafts reaction of substituted arylaldehydes with 2 equivalents of oxygenated arenes under environmentally friendly reaction conditions. Among the overall reaction process, only water was generated as the byproduct. Various reaction conditions are investigated for efficient transformation.

Recent Advancement in the One-Pot Synthesis of the Tri-Substituted Methanes (TRSMs) and Their Biological Applications

The history of tri-substituted methanes (TRSMs) in chemical industries is much older. Tri-substituted methanes were previously used as dyes in the chemical industries. Still, there is a significant surge in researchers' interest in them due to their wide range of bioactivities. Tri-substituted methane derivatives show a wide range of biological activities like anti-tumor, antimicrobial, antibiofilm, antioxidant, anti-inflammatory, anti-arthritic activities. Due to the wide range of medicinal applications shown by tri-substituted methanes, most of the methodologies reported in the literature for the synthesis of TRSMs are focused on the one-pot method. This review explored the recently reported one-pot processes for synthesizing tri-substituted methanes and their various medicinal applications. Based on the substitution attached to the -CH carbon, this review categorizes them into two major classes: (I) symmetrical and (II) unsymmetrical trisubstituted methanes. In addition, this review gives an insight into the growing opportunities for the construction of trisubstituted scaffolds via one-pot methodologies. To the best of our knowledge, no one has yet reported a review on the one-pot synthesis of TRSMs. Therefore, here we present a brief literature review of the synthesis of both symmetrical and unsymmetrical TRSMs covering various one-pot methodologies along with their medicinal applications.

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.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Novel Aryl-Imidazolium Ionic Liquids with Dual Brønsted/Lewis Acidity as Both Solvents and Catalysts for Friedel–Crafts Alkylation

Unique tunable aryl-imidazolium magnetic ionic liquids with dual functions as a solvent–catalyst and dual Brønsted–Lewis acidity (B-L MILs) are applied for Friedel–Crafts alkylation without additional solvents. The catalytic properties of these B-L MILs in the Friedel–Crafts alkylation of p-xylene with benzyl chloride are investigated. The various reaction parameters, including the catalyst dosage, reaction time, reaction temperature, molar ratio of reactants, and reusability, are discussed. The results show that the B-L MIL 5c has more excellent product selectivity (>99%) and reactant conversion (>99%) under the following optimum conditions (reaction temperature = 80 °C, reaction time = 0.5 h, molar ratio of p-xylene to benzyl chloride = 6:1, and catalyst 5c dosage = 1.0 mole %) than traditional catalysts reported in the previous literature. Specifically, due to the mesomeric effect between the FeCl4 anion and hydrogen atom at cationic moiety, the catalyst B-L MILs with the molar fraction of FeCl3 equal to 0.5 can be easily recovered and provide satisfactory catalytic activity after being re-used six times.

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.

Evaluation of Dual 5-Lipoxygenase/Microsomal Prostaglandin E2 Synthase-1 Inhibitory Effect of Natural and Synthetic Acronychia-Type Isoprenylated Acetophenones

Among the pathways responsible for the development of inflammatory responses, the cyclooxygenase and lipoxygenase pathways are among the most important ones. Two key enzymes, namely, 5-LO and mPGES-1, are involved in the biosynthesis of leukotrienes and prostaglandins, respectively, which are considered attractive therapeutic targets, so their dual inhibition might be an effective strategy to control inflammatory deregulation. Several natural products have been identified as 5-LO inhibitors, with some also being dual 5-LO/mPGES-1 inhibitors. Here, some prenylated acetophenone dimers from Acronychia pedunculata have been identified for their dual inhibitory potency toward 5-LO and mPGES-1. To gain insight into the SAR of this family of natural products, the synthesis and biological evaluation of analogues are presented. The results show the ability of the natural and synthetic molecules to potently inhibit 5-LO and mPEGS-1 in vitro. The potency of the most active compound (10) has been evaluated in vivo in an acute inflammatory mouse model and displayed potent anti-inflammatory activity comparable in potency to the drug zileuton used as a positive control.

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.

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.

Deep eutectic solvent catalyzed Friedel–Crafts alkylation of electron-rich arenes with aldehydes

In this study, six deep eutectic solvents were synthesized. Research shows that [ChCl][ZnCl₂]₂ can be used for catalyzing F–C alkylations of electron-rich arenes with aldehydes successfully. After five cycles, the yields remain about 89–94%.

Synthetic methodologies of achiral diarylmethanols, diaryl and triarylmethanes (TRAMs) and medicinal properties of diaryl and triarylmethanes-an overview

This review covers the synthesis of achiral diarylmethanols, diaryl and triarylmethanes and the bioactivities of diaryl and triarylmethanes during 1995 to 2013.

Tandem regioselective synthesis of tetrazoles and related heterocycles using iodine

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.

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.

Synthesis of cinnamyl ethers from α-vinylbenzyl alcohol using iodine as catalyst

Reactions of α-vinylbenzyl alcohol with other alcohols using iodine as a catalyst were investigated. The corresponding cinnamyl ethers were obtained as products. This suggested that α-vinylbenzyl alcohol was converted to cinnamyl ethers via 1-phenylallyl cation. Cinnamyl ethyl ether was obtained in 75% yield by the reaction of α-vinylbenzyl alcohol and ethanol in acetonitrile with iodine under the following conditions: temperature = 50 °C, molar ratio of α-vinylbenzyl alcohol:ethanol:iodine = 1:3.0:0.2, and time period = 6 h. Generally, the yields of the reactions using primary alcohols were higher than those using secondary and tertiary alcohols. Ether interchange also occurred by the reaction of α-vinylbenzyl alcohol and iodine, but proceeded smoothly only when an allyl group was used as the other substituent of the starting ether.