Construction of hydrocarbon belts based on macrocyclic arenes

Hydrocarbon belts have garnered significant attention due to their intriguing structures, unique properties, and potential applications in supramolecular chemistry and materials science. However, their highly inherently strained structures pose challenges in their synthesis, and the resulting tedious synthesis strategies hinder their large-scale applications. Utilizing unstrained macrocyclic arenes as precursors presents an efficient strategy, allowing for a strain-induction step that mitigates the energy barrier associated with building strain in the formation of these belts. Accessible unstrained macrocyclic precursors play a pivotal role in enabling efficient and large-scale syntheses of highly strained belts, facilitating their broader practical applications. This review provides an overview of the recent advancements in the construction of hydrocarbon belts using accessible macrocyclic arenes as building blocks. The synthetic strategies for these partially and fully conjugated hydrocarbon belts are discussed, along with their unique properties. We hope that this review will inspire the development of novel nanocarbon molecules, opening pathways for emerging areas and applications.

Selective Oxidation of Belt[4]arene[4]tropilidene and Its Application to Construct Hydrocarbon Belts of Truncated Cone Structure with Expand Cavity

Despite their unique structures, tantalizing properties, and potential applications in carbon nanoscience and technology, the synthesis and functionalization of zigzag hydrocarbon nanobelts have remained largely unexplored until recently. Reported herein is the selective transformations of belt[4]arene[4]tropilidenes and their application in the construction of novel belts. The oxidation of belt[4]arene[4]tropilidene with benzeneseleninic anhydride under controlled conditions selectively afforded mono- to tetrakis(α-diketone)-functionalized belt intermediates. A subsequent condensation reaction with 1,2-phenylenediacetonitrile and 1,2-phenylenediamine produced a diversity of unprecedented belts with various macrocyclic cavities.

Rigid, biconical hydrogen-bonded dimers that strongly encapsulate cationic guests in solution and the solid state

The octol of a new rigid, tetraarylene-bridged cavitand was investigated for self-assembly behaviour in solution. ¹H and DOSY NMR spectroscopic experiments show that the cavitand readily dimerizes through an unusual seam of interdigitated hydrogen-bonds that is resistant to disruption by polar co-solvents. The well-defined cavity encapsulates small cationic guests, but not their neutral counterparts, restricting the conformation of sequestered tetraethylammonium in solution and the solid state.

A robust, dimeric capsule forms quantitatively in low-polarity solvents via a seam of 8 hydrogen bonds. The resulting electron-rich cavity selectively binds small organic cations over neutral counterparts.

A highly sensitive "ON-OFF-ON" dual optical sensor for the detection of Cu(II) ion and triazole pesticides based on novel BODIPY-substituted cavitand

The synthesis with full structural characterization including elemental analysis and 1H, 13C, 11B and 19F NMR, FT-IR and MALDI-TOF spectral data, along with the florescence sensing behavior of a new resorcin[4]arene cavitand 3 bearing multiple BODIPY sites achieved by the Cu-catalyzed azide-alkyne cycloaddition (CuAAC) is being reported. The spatial orientation of multiple BODIPY-1,2,3-triazole arms based on the macrocyclic rigid core is of great interest since the resulting structure has been utilized as a fluorescent chemosensor for numerous metal cations. In particular, a remarkable decrease in the fluorescence emission towards Cu(ii) ions, i.e., "turn-off" response, has been obtained giving rise to an optical sensor for the detection of triazole fungicides, namely tebuconazole, triadimenol, triadimefon, i.e. "turn-on" response. Such a molecular system, hence, can be feasibly applied as a dual optical sensor, i.e. "a turn-on-off-on" system, for dangerous contaminants such as heavy metals and pesticides.

Resorcin[4]arene-based multidentate phosphate ligands with superior binding affinity for nanocrystal surfaces

We designed and synthesized two resorcin[4]arene scaffolds with four phosphate binding groups. The ligands effectively bind in at least a tridentate fashion at low surface coverage. The superior binding affinity is demonstrated using solution NMR spectroscopy and exceeds that of single phosphonates.

Regioconvergent Synthesis of a π-Extended Tribenzotriquinacene-Based Wizard Hat-Shaped Nanographene

The successful enlargement of the curved π-electron periphery of the wizard hat-shaped polycyclic aromatic compound 1 is described. The target structure 2 features an m,m,p,m,m,p,m,m,p-nonaphenylene belt fused to a central tribenzotriquinacene unit. The synthesis involves a multiple regioconvergent Scholl-type dehydrocyclization as the key step. Spectroscopic, structural, and electronic properties of the title compound 2 are reported.

A helically twisted ribbon-shaped nanographene constructed around a fenestrindane core

Ten C–C bonds and four cycloheptatriene rings were formed in one single operation, producing a helically twisted ribbon-shaped nanographene in 11% yield.

Catechol[4]arene: The Missing Chiral Member of the Calix[4]arene Family

A missing, inherently chiral member of the calix[4]arene family denoted "catechol[4]arene" was synthesized. Its properties were studied and compared to the ones of its close relatives resorcin[4]arene and pyrogallol[4]arene. This novel supramolecular host exhibits binding capabilities that are superior to its sister molecules in polar media. The enantiomerically pure forms of the macrocycle display modest recognition of chiral ammonium salts.

One-Step Synthesis of C2v-Symmetric Resorcin[4]arene Tetraethers

The three-component reaction between a resorcinol, 1,3-dimethoxybenzene, and an alkyl aldehyde (R = C₁-C₁₁) along with BF₃·OEt₂ affords a C_2v-symmetric resorcin[4]arene tetraether in one step; in most cases, the single isomer can be precipitated from the reaction mixture in moderate to excellent yields (up to 89%). The reaction is tolerant of 2-substituted resorcinols (R' = OH, Cl, Br, Me), allowing a third type of functionality to be regioselectively incorporated during the macrocyclization.

Toward the Synthesis of a Highly Strained Hydrocarbon Belt

Hydrocarbon belts including fully conjugated beltarenes and their (partially) saturated analogs have fascinated chemists for decades due to their aesthetic structures, tantalizing properties, and potential applications in supramolecular chemistry and carbon nanoscience and nanotechnology. However, synthesis of hydrocarbon belts still remains a formidable challenge. We report in this communication a general approach to hydrocarbon belts and their derivatives. Closing up all four fjords of resorcin[4]arene derivatives through multiple intramolecular Friedel-Crafts alkylation reactions in an operationally simple one-pot reaction manner enabled efficient construction of octohydrobelt[8]arenes. Synthesis of belt[8]arene from DDQ-oxidized aromatization of octohydrobelt[8]arene under different conditions resulted in aromatization and simultaneous [4 + 2] cycloaddition reactions with DDQ or TCNE to produce selectively tetrahydrobelt[8]arene-DDQ₂, tetrahydrobelt[8]arene-TCNE₂, and belt[8]arene-DDQ₄ adducts. Formation of belt[8]arene, a fully conjugated hydrocarbon belt, was observed from retro-Diels-Alder reaction of a belt[8]arene-DDQ₄ adduct with laser irradiation under MALDI conditions. The new and practical synthetic method established would open an avenue to create belt-shaped molecules from easily available starting materials.

Synthetic Applications of Oxidative Aromatic Coupling-From Biphenols to Nanographenes

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

Metal-Assembled, Resorcin[4]arene-Based Molecular Trimer for Efficient Removal of Toxic Dichromate Pollutants and Knoevenagel Condensation Reaction

Self-assembly of resorcin[4]arene-based coordination cages involving more than two resorcin[4]arenes poses significant challenges for the requirements of suitable functionalized resorcin[4]arene ligands and metals. Here, we report an unusual example of a metal-coordinated, resorcin[4]arene-based molecular trimer (1-NO₃), composed of three resorcin[4]arenes and three Cd(II) cations. In particular, 1-NO₃ features efficient and selective removal of environmentally toxic dichromate (Cr₂O₇^2-) anions. Moreover, the Knoevenagel condensation reaction was also explored by using 1-NO₃ as an efficient heterogeneous catalyst.