Synthesis of Distorted 1,8,13-Trisilyl-9-hydroxytriptycenes by Triple Cycloaddition of Ynolates to 3-Silylbenzynes

1,8,13-Trialkyl(aryl)silyl-9-hydroxytriptycenes (trisilyltriptycenes) were synthesized by the triple addition of ynolates and 3-silylbenzynes with high regioselectivity. Benzene rings in the resulting triptycenes were highly distorted where the dihedral angles between the substituents were as high as 35°. The distortion energy induced step-by-step halogenation reactions to yield halogenated triptycenes, including chiral triptycenes. The 1,8,13-trihalogenated triptycenes were then converted to 1,8,13-functionalized triptycenes.     

Regioselective One‐Pot Synthesis of Triptycenes via Triple‐Cycloadditions of Arynes to Ynolates

We developed the novel one‐pot synthetic method of substituted triptycenes by the reaction of ynolates and arynes. This four‐step process involves three cycloadditions and electrocyclic ring opening of the strained Dewar anthracene. Each of the three related but structurally distinct classes of nucleophiles (ynolate, enolate, and anthracenolate) reacts with o‐benzyne in the same predictable manner controlled by chelation and negative hyperconjugation. The resulting functionalized C₃‐symmetrical triptycenes hold promise in the design of functional materials.     

Quadruple Role of Pd Catalyst in Domino Reaction Involving Aryl to Alkyl 1,5-Pd Migration to Access 1,9-Bridged Triptycenes

A Pd-catalyzed domino reaction of 1,8,13-tribromo-9-methoxytriptycenes is reported. Under conventional Suzuki coupling conditions, the triptycenes underwent multiple transformations to give 1,9-bridged triptycenes. Based on mechanistic investigations, a single Pd catalyst functions as Pd⁰, Pd^II and Pd^IV species to catalyze four distinct processes: (1) aryl to alkyl 1,5-Pd migration, (2) intramolecular arylation, (3) homocoupling of phenylboronic acid and (4) Suzuki coupling. DFT calculations revealed that 1,5-Pd migration likely proceeds via both concerted Pd^II and stepwise Pd^IV routes. Asymmetric synthesis of the chiral triptycenes, as well as optical resolution, and further transformation are also reported.     

Tetrathiafulvalene-functionalized triptycenes: synthetic protocols and elucidation of intramolecular Coulomb repulsions in the oxidized species

A large selection of triptycenes functionalized with tetrathiafulvalene (TTF) units as well as triptycenes containing extended TTFs as a part of the triptycene core have been synthesized utilizing new triptycene di- and tetraaldehydes as well as bis-, tetrakis- and hexakis(bromomethyl) derivatives. The largest scaffold contains a total of 12 TTFs around the central triptycene core. From spectroelectrochemical and chemical oxidation studies, we have elucidated the extent to which an increasing number of electrostatic interactions among oxidized TTF units exert an influence on the absorption characteristics.     

Using "internal free volume" to increase chromophore alignment

Triptycenes have general applicability for increasing the alignment of fluorescent and dichroic dyes in LC hosts. Dyes containing varying numbers of triptycenes were synthesized to study the effect of free-volume alignment of triptycenes on the alignment of dyes. These dyes were designed such that multiple triptycenes could be incorporated and the triptycene-free volume is coincident to the aspect ratio of the dye, allowing a cooperative effect to increase their overall average alignment. With increasing triptycene incorporation, a stepwise increase in the alignment parameters of each dye was seen. It was also found that the attachment of one triptycene group has a negligible effect on the optical switching response times of the dyes. This can be a powerful tool for designing dyes with higher alignments for a variety of applications including guest-host reflective LCDs and holographic data storage.     

Chiral Iodotriptycenes: Synthesis and Catalytic Applications

Invited for this month′s cover picture is the group of Thomas Wirth at Cardiff University (UK). The cover picture shows two structures of triptycenes. In each of these molecules all three aromatic rings are different with the rigid structure of the molecules making them chiral. The two sp³-carbons shown in red and green are the stereocentres with defined configuration. These molecules contain the crucial iodine functionality which are utilised to generate hypervalent iodine(III)-catalysts in situ . The authors acknowledge Dr. Yu Wang for the creation of the cover image. Read the full text of their Research Article at 10.1002/open.202200145 .     

Enantioselective Synthesis of Distorted π-Extended Chiral Triptycenes Consisting of Three Distinct Aromatic Rings by Rhodium-Catalyzed [2+2+2] Cycloaddition

The enantioselective synthesis of distorted π-extended chiral triptycenes, consisting of three distinct aromatic rings, has been achieved with high ee value of 87 % by the cationic rhodium(I)/segphos complex-catalyzed enantioselective [2+2+2] cycloaddition of 2,2′-di(prop-1-yn-1-yl)-5,5′-bis(trifluoromethyl)-1,1′-biphenyl with 6-methoxy-1,2-dihydronaphthalene followed by the diastereoselective Diels–Alder reaction and aromatization. Demethoxy derivatives were also synthesized by the C−O bond cleavage. In this synthesis, the use of the electron-deficient diyne and the electron-rich alkene is crucial to suppress the undesired strain-relieving carbocation rearrangement and stabilize the distorted triptycene structure.     

Naphthalimide‐Based Triptycenes: Synthesis and Optoelectronic Properties

In the past decades, the naphthalimide structure has found application in many areas of chemistry due to its unique photophysical properties. Naphthalimide has two isomers, 1,8‐naphthalimide containing a six‐membered imide ring and 2,3‐naphthalimide containing a five‐membered imide ring. The former has been widely investigated while studies on the latter are considerably more rare. On the other hand, naphthalimide can also be regarded as a building block to construct polycyclic aromatic hydrocarbons (PAHs), which have found wide applications in optical materials. Here we report the synthesis and optoelectronic properties of three 2,3‐naphthalimide‐based triptycenes. These three triptycene derivatives enrich the family of triptycenes.     

Synthesis of self-orienting triptycene adsorbates for STM investigations

The syntheses of three C₂ symmetric triptycenes containing two pendant groups are described. The pendant groups are designed to promote oriented adsorption to graphite or gold electrodes such that the unfunctionalized aryl group extends perpendicular to the surface. Initial STM studies are consistent with oriented adsorption on graphite.     

Chiral Triptycenes in Supramolecular and Materials Chemistry

Triptycenes are an intriguing class of organic molecules with several unusual characteristics, such as a propeller-like shape, saddle-like cavities around a symmetrical scaffold, a rigid π-framework. They have been extensively studied and proposed as key synthons for a variety of applications in supramolecular chemistry and materials science. When decorated with an appropriate substitution pattern, triptycenes can be chiral, and, similarly to other popular chiral π-extended synthons, can express chirality robustly, efficiently, and with relevance to chiroptical spectroscopies. This minireview highlights and encompasses recent advances in the synthesis of chiral triptycenes and in their introduction as molecular scaffolds for the assembly of functional supramolecular materials.     

Synthesis and structures of triptycene-derived Tröger's base molecular clips

A series of triptycene-derived Tröger’s bases with molecular clip shaped structures have been efficiently synthesized by one-pot condensation of corresponding amino-substituted triptycenes with paraformaldehyde in trifl uoroacetic acid.     

Triptycene polymers

New, bifunctional, bridgehead-substituted triptycenes were synthesized and used to prepare a series of triptycene polymers, including polyesters, polyamides, polyurethanes, and a polyoxadiazole. Certain of these partially aliphatic polymers were thermally stable. Clear and colorless films were obtained in some instances.     

New Procedure for the Synthesis of 2-Alkylbenzimidazoles

Simple, economical, and environmentally friendly method to synthesize 2-alkylbenzimidazoles was developed by modifying the conventional method between o-phenylenediamine and aldehyde.     

The synthesis of perfluoro-1,6-disubstituted triptycenes containing group IV and group V elements

The step-wise syntheses, starting from 1,2-dibromotetrafluorobenzene, of eight fully-fluorinated 1,6-disubstituted triptycenes is described. In each case the intermediate tris(2-bromotetrafluorophenyl) compounds were isolated and characterized.     

Synthesis and structures of Hexa-peri-hexabenzocoronene-based triptycenes

A series of Hexa-peri-hexabenzocoronene-based triptycenes bearing mono-, di-, or tri-HBC moieties were synthesized from iodotriptycenes. Their structures were determined by NMR, MS spectra, and X-ray analysis. The planar HBC moieties displayed strong deshielding effect to triptycene scaffold, resulting in significant downfield chemical shift of the two methenyl protons. Moreover, the HBC units are well separated in the triptycene scaffold, without quenching the fluorescent properties of each HBC unit.     

Synthesis and structure of 2,6,14- and 2,7,14-trisubstituted triptycene derivatives

A series of 2,6,14- and 2,7,14-trisubstituted triptycene derivatives were efficiently synthesized and their structures were determined by NMR, MS spectra, and X-ray analysis. These trisubstituted triptycenes are potential building blocks for constructing novel receptors and synthetic molecular machines.     

Triptycene: no homoconjugation effect for extending optical properties of π-conjugated oligomers

1,5- and 1,8-bis(bifluorenyl)anthracene were synthesized and converted to their corresponding bis(bifluorenyl)triptycenes and bis(bifluorenyl)-9,10-dihydroanthracenes. Analysis of their optical properties shows no feature of extended conjugation in the triptycene pair. The electronic spectra of the triptycene and dihydroanthracene pairs are in fact superimposable. There is definite evidence that triptycene displays zero homoconjugation effect.     

Facile Synthesis of Monofluoro γ-Lactones and Pyrrolidine Derivatives via Electrophilic Fluorination of Allenoic Acids and Amides

A convenient method to synthesize a series of monofluoro γ-lactones and pyrrolidine derivatives in moderate to good yields via the electrophilic fluorination of γ-allenoic acids and tosylamides using Selectfluor was developed.     

Heterocyclic triptycenes : Synthesis and ultraviolet spectroscopy

The synthesis of some heterocyclic triptycenes is reported. A study of the UV spectra of these and analogous compounds was undertaken. Two series of compounds were prepared: 9,10-bridged anthracene compounds and 5,12-bridged naphthacene compounds. The results from these studies alone are inconclusive. However if calculations are made, based on interannular π-π interactions between the aromatic rings in these systems, the calculated N → V₁ transitions and longest wavelength absorption maxima give a straight line when plotted.