Recent advances in the chemistry of triaryl- and triheteroarylmethanes

Organocatalytic enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides: access to unsymmetrical triarylmethanes

The enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides has been achieved with the aid of a chiral phosphoric acid. Importantly, the reaction took place with excellent chemo- and regioselectivities. In addition, the protocol features a low catalyst loading, mild reaction conditions, and enables the formation of unsymmetrical triarylmethanes in good to high yields with generally high enantioselectivities.

The enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides has been achieved with the aid of a chiral phosphoric acid.

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.

Fluorinated Alcohol-Promoted Reaction of Chlorohydrocarbons with Diverse Nucleophiles for the Synthesis of Triarylmethanes and Tetraarylmethanes

This article reports an efficient synthesis of triarylmethanes and tetraarylmethanes from chlorohydrocarbons with miscellaneous nucleophiles in fluorinated alcohols, featuring metal-free, wide substrate scope, excellent functional group tolerance, and mild reaction conditions.

(-)- and (+)-Securidanes A and B, Natural Triarylmethane Enantiomers: Structure and Bioinspired Total Synthesis

Two pairs of enantiomers, (-) and (+)-securidanes A (1 and 2) and B (3 and 4) featuring unprecedented triarylmethane (TAM) skeletons, were isolated from Securidaca inappendiculata. Their structures were established by spectroscopic data, X-ray crystallography, and CD analysis. A plausible biosynthetic pathway for 1-4 based on the co-isolated precursors was proposed. Bioinspired total synthesis of 1-4 was completed in high yield, which in turn corroborated the biosynthetic hypothesis. Compounds 1-4 showed good inhibition against protein tyrosine phosphatase 1B (PTP1B). The molecular docking demonstrated that the strongest inhibitor 3 (IC₅₀ = 7.52 μM) reaches deeper into the binding pocket and has an additional H-bond.

Chiral Phosphoric Acid Catalyzed Asymmetric Synthesis of Hetero-triarylmethanes from Racemic Indolyl Alcohols

The direct enantioselective 1,4- and 1,8-arylations of 7-methide-7H-indoles and 6-methide-6H-indoles, respectively, generated in situ from diarylmethanols, with electron-rich arenes as nucleophiles, has been achieved in the presence of chiral phosphoric acids (CPAs). These two remote activation protocols provide an efficient approach for the construction of diverse hetero-triarylmethanes in high yields (up to 97 %) and with excellent enantioselectivities (up to 96 %). Mechanistically inspired experiments tentatively indicate that the catalytic enantioselective 1,4-addition as well as the formal S_N 1 substitution could proceed efficiently in the similar catalytic systems. Furthermore, the modification of the catalytic system and diarylmethanol structure successfully deviates the reactivity toward a remote, highly enantioselective 1,8-arylation reaction. This flexible activation mode and novel reactivity of diarylmethanols expand the synthetic potential of chiral phosphoric acids.

Catalyst-Free 1,6-Conjugate Addition/Aromatization/Sulfonylation of para-Quinone Methides: Facile Access to Diarylmethyl Sulfones

An efficient, catalyst-free strategy to construct diarylmethyl sulfones via 1,6-conjugate addition/aromatization/sulfonylation reaction of para-quinone methides with sulfonyl hydrazides under mild and environmentally benign conditions has been developed. The established protocol provided a highly chemo- and regioselectivity synthesis of a diverse array of novel diarylmethyl sulfones with excellent yields, and the reaction could be scaled up.

Unmasking Dipole Character of Acyl Ketene Dithioacetals via a Cascade Reaction with Arynes: Synthesis of Benzo[b]thiophenes

An unusual strategy toward novel substituted benzo[b]thiophenes has been developed. The generation of arynes in the presence of acyl ketene dithioacetals resulted in a cascade reaction involving [3 + 2] cycloaddition, and a dealkylative arylation of a thioether moiety to afford 2,3-disubstuted benzo[b]thiophenes. This route represents an expeditious approach to benzothiophenes that employs acyl ketene dithioacetals as dipoles.

Self-reversible mechanochromism and aggregation induced emission in neutral triarylmethanes and their application in water sensing

Neutral triarylmethanes exhibit intramolecular exciplex formation, self-reversible mechanochromism, and aggregation induced/viscosity-dependent emission and sense water in organic solvents.

Silver-catalyzed direct benzylation of acetanilide: a highly efficient approach to unsymmetrical triarylmethanes

A highly efficient silver-catalyzed dibenzylation of acetanilides by employing the benzhydrol derivatives as the coupling partners to yield triphenylmethane derivatives has been developed. Various functional groups were tolerated, leading to the corresponding products in moderate to good yields. Preliminary experimental results indicated that the silver ions activate the arene rings and the strong acid TfOH provides the carbocations.

An efficient approach for the synthesis of triphenylmethanes through the direct combination of acetanilides and diphenylmethanol derivatives using AgOTf as the catalyst has been developed.

A highly efficient nucleophilic substitution reaction between R2P(O)H and triarylmethanols to synthesize phosphorus-substituted triarylmethanes

A highly efficient nucleophilic substitution reaction between R₂P(O)H and triarylmethanols was reported, which provides phosphorus-substituted triarylmethanes in rich diversity with 40–96% yields.

Fe(OTf)3-catalysed Friedel-Crafts reaction of benzenoid arenes with α,β-unsaturated carbonyl compounds: easy access to 1,1-diarylalkanes

A simple and efficient method for the synthesis of 1,1-diarylalkanes via the Friedel-Crafts-type alkylation reaction of electron-rich arenes with cinnamic acid ester derivatives or chalcones is reported. Iron triflate has been found to be the best catalyst for the Friedel-Crafts-type alkylation reaction with α,β-unsaturated carbonyl compounds. This reaction afforded β,β-diaryl carbonyl compounds in good yields (65-93%) and with excellent regioselectivities. Remarkably, this method is also compatible with a variety of indoles to provide 3-indolyl-aryl carbonyl compounds in excellent yields. Great efforts have been made to deduce a plausible reaction mechanism based on isotopic labelling experiments.

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.

Access to Enantiopure Triarylmethanes and 1,1-Diarylalkanes by NHC-Catalyzed Acylative Desymmetrization

We present herein an unprecedented, efficient and enantioselective synthesis of triarylmethanes and 1,1-diarylalkanes through N-heterocyclic carbene-catalyzed acylative desymmetrization of bisphenols. This method utilizes readily available substrates, reagents and a simple procedure to deliver the valuable products in excellent enantiopurity. DFT calculations reveal that the selectivity is governed by the C-C bond cleavage step of the tetrahedral intermediate leading to the ester product. A transition state model featuring a combination of intramolecular hydrogen bond and steric effect is developed to explain the enantioselectivity.

Efficient access to triarylmethanes through decarboxylation

A new approach has been developed for diverse triarylmethanes by palladium catalyzed decarboxylative sp²–sp³ cross coupling where benzoic acids reacted with diaryl methyl iodides having both electron donating and withdrawing functionalities.

Physicochemical and Electronic Properties of Cationic [6]Helicenes: from Chemical and Electrochemical Stabilities to Far-Red (Polarized) Luminescence

The physicochemical properties of cationic dioxa (1), azaoxa (2), and diaza (3) [6]helicenes demonstrate a much higher chemical stability of the diaza adduct 3 (pKR+ =20.4, Ered1/2 =-0.72 V) compared to its azaoxa 2 (pKR+ =15.2, Ered1/2 =-0.45 V) and dioxa 1 (pKR+ =8.8, Ered1/2 =-0.12 V) analogues. The fluorescence of these cationic chromophores is established, and ranges from the orange to the far-red regions. From 1 to 3, a bathochromic shift of the lowest energy transitions (up to 614 nm in acetonitrile) and an enhancement of the fluorescence quantum yields and lifetimes (up to 31 % and 9.8 ns, respectively, at 658 nm) are observed. The triplet quantum yields and circularly polarized luminescence are also reported. Finally, fine tuning of the optical properties of the diaza [6]helicene core is achieved through selective and orthogonal post-functionalization reactions (12 examples, compounds 4-15). The electronic absorption is modulated from the orange to the far-red spectral range (560-731 nm), and fluorescence is observed from 591 to 755 nm with enhanced quantum efficiency up to 70 % (619 nm). The influence of the peripheral auxochrome substituents is rationalized by first-principles calculations.

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.

Novel stilbene-based Fischer base analog of leuco-TAM - (2E,2'Z)-{2-(4-(E)-styrylphenyl)propane-1,3-diylidene}bis(1,3,3-trimethylindoline) - derivatives: synthesis and structural consideration by 1D NMR and 2D NMR spectroscopy

We report the synthesis of a series of novel stilbene-based (St) Fischer base analogs of leuco-triarylmethane (LTAM) dyes by treating Fischer base with (E)-4-styrylbenzaldehyde derivatives. All St-LTAM molecules examined herein are characterized by 1D and 2D NMR. They were found to exhibit ZE configuration and isomerize to their diastereomers EE and ZZ in 2-3 h. They exhibit type I behavior of diastereomeric isomerization.

Chiral phosphoric acid catalyzed asymmetric addition of naphthols to para-quinone methides

An asymmetric addition of naphthols to in situ generated para-quinone methides catalyzed by a chiral phosphoric acid is described.

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.

Bismuth(iii)dichalcogenones as highly active catalysts in multiple C–C bond formation reactions

Thirteen new bismuth(iii) dichalcogenone derivatives with diversified structural motifs were successfully isolated and used as potential catalysts for the synthesis of triaryl- or triheteroarylmethanes.

Expedient access to unsymmetrical triarylmethanes through N-heterocyclic carbene catalysed 1,6-conjugate addition of 2-naphthols to para-quinone methides

A direct and atom-economical protocol for the synthesis of unsymmetrical triarylmethanes through 1,6-conjugate addition of 2-naphthols topara-quinone methides using N-heterocyclic carbene as a Brønsted base catalyst is described.