Cyclophanes have been firmly entrenched as a distinct class of compounds for well over half a century. The two main factors that have kept this field of chemistry going so strongly for such a long time are tremendous structural diversity and the interesting behaviour that is often observed. Although a very large number cyclophanes has been reported, only a very small proportion of them contain polycyclic aromatic systems that can be thought of as “large”, i.e. with ≥4 rings. This Review puts the spotlight on such cyclophanes, illuminating both the chemistry that was used to synthesize them and what was learned from studying them. Context for the main body is provided by the careful consideration of the anatomy of a cyclophane and the classification of general synthetic approaches. The subsequent sections cover eleven different PAHs and are organized primarily according to increasing size of the aromatic system, starting with pyrene (C16, the only large polycyclic aromatic system to have been incorporated into numerous cyclophanes) and ending with hexabenzo[bc,ef,hi,kl,no,qr]coronene (C42).

Cyclophanes containing large polycyclic aromatic hydrocarbons

In 1976, the first attempted synthesis of the saddle-shaped molecule [8]circulene was reported. The next 37 years produced no advancement towards the construction of this complicated molecule. Remarkably, however, over the last six months a flurry of progress has been made with two groups reporting independent and strikingly different strategies for the synthesis of [8]circulene derivatives. Herein, we present a third synthetic method in which we target tetrabenzo[8]circulene. Our approach employs a Diels-Alder reaction and a palladium-catalyzed arylation reaction as the key steps. Despite calculations describing the instability of [8]circulene, coupled with the reported instability of synthesized derivatives of the parent molecule, the addition of four fused benzenoid rings around the periphery of the molecule provides a highly stable structure. This increased stability over the parent [8]circulene was predicted using Clar’s theory of aromatic sextets and is a result of the compound becoming fully benzenoid upon incorporation of these additional rings. The synthesized compound exhibits remarkable stability under ambient conditions – even at elevated temperatures – with no signs of decomposition over several months. The solid-state structure of this compound is significantly twisted compared to the calculated structure primarily as a result of crystal packing forces in the solid state. Despite this contortion from the lowest energy structure, a range of structural data is presented confirming the presence of localized aromaticity in this large polycyclic aromatic hydrocarbon.

Synthesis and structural data of tetrabenzo[8]circulene.

The structural characterization of nanoporous carbons is a challenging task as they generally lack long-range order and can exhibit diverse local structures Such characterization represents an important step toward understanding and improving the properties and functionality of porous carbons, yet few experimental techniques have been developed for this purpose Here we demonstrate the application of nuclear magnetic resonance (NMR) spectroscopy and pair distribution function (PDF) analysis as new tools to probe the local structures of porous carbons, alongside more conventional Raman spectroscopy Together, the PDFs and the Raman spectra allow the local chemical bonding to be probed, with the bonding becoming more ordered for carbide-derived carbons (CDCs) synthesized at higher temperatures The ring currents induced in the NMR experiment (and thus the observed NMR chemical shifts for adsorbed species) are strongly dependent on the size of the aromatic carbon domains We exploit this property and use co

/pdf/new-insights-into-the-structure-of-nanoporous-carbons-from-1av0120t76.pdf

New Insights into the Structure of Nanoporous Carbons from NMR, Raman, and Pair Distribution Function Analysis

A contorted polycyclic aromatic hydrocarbon (PAH) in the shape of a monkey saddle has been synthesized in three steps from a readily available truxene precursor. The monkey saddle PAH is consisting of three five-, seven six-, and three eight-membered rings and has been unambiguously characterized by single-crystal X-ray diffraction. Owing to the three biaryl axes the monkey saddle PAH is inherently chiral. The inversion of the two enantiomeric structures into each other preferably occurs through a twisting of peripheral rings rather than by a fully planar intermediate, as has been calculated by DFT methods. Enantiomers were separated by chiral HPLC and inversion barriers determined by variable temperature circular dichroism spectroscopy, supporting the twisting mechanism.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/anie.201912213

A Chiral Polycyclic Aromatic Hydrocarbon Monkey Saddle

NMR studies of cyclophanes

Saddle-shaped [7]circulene (1) is prepared by an extremely simple procedure that involves a 2,15-ethano-bridged hexahelicene intermediate. Reduction properties of the [7]circulene have been investigated by means of voltammetry and ESR spectroscopy and compared with those of planar [6]circulene (coronene) (2).

Convenient synthesis and reduction properties of [7]circulene

The syntheses of the title compounds are described. The unusually strained structures were supported by their 1H NMR spectra, electronic spectra, and X-ray crystallographic analyses.

An Attempted Synthesis of 8-Shaped Circulene: Synthesis and Characterization of [2.2](4,4′)Biphenylo(3,11)dibenzo[c, l]chrysenophane and Its Cyclophadiene

The synthesis of the title compound, a triple-layered cyclophane, is described. The unusually strained structure was supported by its 1H NMR spectra, electronic spectra, and X-ray crystallographic analysis.

An Attempted Synthesis of [7][7]Circulene: Synthesis and Characterization of Triple-Layered [2.2]Phenanthreno[2.2]naphthalenophenanthrenophane

High-dilution coupling of 5,13-bis(bromomethyl)dibenzo[c;1]chrysene (7) and 5,13-bis(sulfanylmethyl)dibenzo[c;1]chrysene 8 afforded the dithia derivative 9 which was converted, via the disulfone 10, into an unusually strained compound, [2.2](5,13)dibenzo[c;1]chrysenophane 5.

https://journals.sagepub.com/doi/pdf/10.1177/174751989902300112

Synthesis and Characterisation of [2.2](5,13)Dibenzo[c;1]chrysenophane

Syntheses and Characterizations of Dibenzochrysenophane and Biphenylodibenzochrysenophane Directed Toward Preparation of 8-shaped Closed Circulenes

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