A Quintuple [6]Helicene with a Corannulene Core as a <i>C</i><sub>5</sub>‐Symmetric Propeller‐Shaped π‐System

Kato, Kenta; Segawa, Y.; Scott, Lawrence T.; Itami, Kenichiro

doi:10.1002/anie.201711985

Cited by 156 publications

(66 citation statements)

References 86 publications

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“…It should be noted that all efforts towards extending the [13]helicene (25), using the presented method with 2-naphthol (20)o r3 -Scheme 1. Previous reported synthesis of diazadioxa [8]circulene (12) and the herein reported synthesis of novel diazaoxa [7]helicene (15). Important intermediates are shown in brackets.…”

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confidence: 88%

“…This has been used in the construction of state‐of‐the‐art optical devices for the detection or emission of circularly polarized light . The past few years have witnessed a boom in the synthesis of helical aromatic systems containing expanded, elongated, or extended helicenes . These molecules typically display interesting optical properties and complex chiral behavior .…”

Section: Figurementioning

confidence: 99%

“…Theinspiration for the synthesis of the presented azaoxa-[n]helicenes stems from our previous reported syntheses of diazadioxa [8]circulenes (12;S cheme 1, top). Treating 3,6dihydroxycarbazole (13)w ith an oxidant (chloranil) and aLewis acid (BF 3 ·OEt 2 )allowed for the one-pot preparation of the corresponding diazadioxa [8]circulenes (12)i n8 5% yield. [22] Mechanistically,the formation of 12 proceeds via an initial oxidative coupling of 13,mediated solely by the oxidant to give 14.…”

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confidence: 99%

“…[22] Mechanistically,the formation of 12 proceeds via an initial oxidative coupling of 13,mediated solely by the oxidant to give 14. [23] Thecombination of both oxidant and Lewis acid mediates the furan forming dehydration forming adiazaoxa- [7]helicene (15)i ntermediate.R epetition of the oxidative furan formation between the hydroxy termini of 15 forms the diazadioxa [8]circulene (12). In the work presented herein, the final [8]circulene forming oxidative furan formation is avoided by ap rotecting-group strategy.W eh ave developed two procedures to access diazaoxa [7]helicene 15 (Scheme 1b, Methods Aa nd B).…”

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Symmetric, Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

2019

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Fully aromatic helicenes with more than one pitch‐length are illustrious synthetic targets with potential applications in advanced optical devices and nano‐electronics. The task of extending the length of fully conjugated helicenes past one pitch length is challenging. Now, the synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The flexibility of the presented method allows the convenient and scalable synthesis of symmetric, unsymmetrical, and asymmetric homo‐chiral structures. The [13]helicenes can be synthetically functionalized both at the termini and the periphery. The full range of helicenes were characterized using NMR and optical spectroscopy (UV/Vis, fluorescence, and CD) along with single‐crystal X‐ray crystallography. The enantiomers of the [13]helicenes are the longest optically pure helicenes isolated to date.

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confidence: 88%

Section: Figurementioning

confidence: 99%

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confidence: 99%

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Symmetric, Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

2019

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“…For example, Itami et al. reported corannulene‐based chiral nanocarbons and Maçôas and Campaña et al. reported a chiral ribbon‐shaped nanographene .…”

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confidence: 99%

Chirality‐Embedded Nanographenes

2019

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The development of chiral nanographenes has mostly been carried out by bottom‐up methods and examples of species developed by the post‐modification of nanographenes prepared by top‐down methods remain limited. We show that the attachment of chiral functional groups onto the edge of nanographenes generates chirality on the surface. X‐ray diffraction analysis and DFT calculations indicate that the chirality of the functional groups is transferred to the surface via steric interactions from the chiral center through the five‐membered cyclic imide to the nanographene edge. The exciton coupling between the p‐bromophenyl groups confirms that the functional groups are arranged on the armchair edges at distances that permit exciton coupling, which provides information about their relative orientation. These pieces of information help to elucidate the edge structure of nanographenes prepared by top‐down methods.

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