Helicene

Short description: Class of chemical compounds

Hexahelicene

General structure formula of [n]helicene

In organic chemistry, helicenes are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped chiral molecules.[1] The chemistry of helicenes has attracted continuing attention because of their unique structural, spectral, and optical features.[2][3][4][5][6][7][8]

## Contents

* 1 Structure and properties
* 2 Synthesis
* 3 Applications
* 4 See also
* 5 References

## Structure and properties

The systematic naming for this class of compounds is based on the number of rings: [n]helicene is the structure consisting of n rings. According to IUPAC, only structures where n is at least 5 are considered helicenes.[1] Some specific compounds also have alternate or trivial names. As the number of rings increases, starting at four, the structure becomes non-planar, but instead the planes of consecutive rings tilt to prevent steric collisions. For helicenes with six benzene units, a 360° turn is completed. In the helicene series the dihedral angles between the extremities increases going from [4]helicene (26°) to [6]helicene (58°) and then decreases again for example in [7]helicene (30°).

Helicenes are notable for having chirality despite lacking both asymmetric carbons and chiral centers. Instead, there is axial chirality, which results from the handedness of the helicity itself. The clockwise and counterclockwise helices are non-superposable. By convention a left-handed helix is minus and labeled (M), a right-handed helix is plus and labeled (P). Evidence from CD spectroscopy suggests left-handed helices are levorotatory and right-handed helices are dextrorotatory.

The stability of the two complementary helical enantiomers with respect to interconversion and the mechanism by which they interconvert depend on n.[9]

## Synthesis

The first helicene structure was reported by Jakob Meisenheimer in 1903 as the reduction product of 2-nitronaphthalene.[10] [5]helicene was synthesized in 1918 by Weitzenböck & Klingler.[11] The first [6]helicene (also called hexahelicene) was synthesized by M. S. Newman and D. Lednicer in 1955 via a scheme that closed the two central rings by Friedel–Crafts cyclization of carboxylic acid compounds.[12][13] Since then, several methods for synthesizing helicenes with different lengths and substituents are used. The oxidative photocyclization of a stilbene-type precursor is used most often as the key step. The longest helicene prepared by this method is [16]helicene in 2015.[citation needed]

In one study,[14] [5]helicene was synthesized in an olefin metathesis reaction of a divinyl compound (prepared from 1,1′-bi-2-naphthol (BINOL) in several steps), with Grubbs' second generation catalyst:

Other approach is also non-photochemical and is based on assembly of biphenylyl-naphthalenes and their platinum-catalyzed double cycloisomerization leading to various [6]helicenes:[15]

* [4]Helicene

* [5]Helicene

* [6]Helicene

* [6]Helicene, other chirality

* [7]Helicene

* [7]Helicene, other chirality

* [8]Helicene

* [9]Helicene

* [10]Helicene

* [11]Helicene

* [12]Helicene

* [13]Helicene

* [14]Helicene

* [15]Helicene

* [16]Helicene

* [18]Helicene

## Applications

Helicenes have been studied with respect to nonlinear optics,[16] CPL,[17][18] organocatalysis,[19] conformational analysis,[20] chirality sensing,[21] chemical sensors[22] and hetero-atom substitution.[23][24][25][26]

## See also

* Other configurations of consecutively-fused benzene rings:
* Acenes, linear
* Phenacenes, zig-zag
* Circulenes, closed ring

## References

1. ↑ 1.0 1.1 IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "helicenes". doi:10.1351/goldbook.H02762
2. ↑ Martin, R. H. (1974), The Helicenes. Angew. Chem. Int. Ed. Engl., 13: 649–660. doi:10.1002/anie.197406491
3. ↑ Helicenes: Synthesis and Applications Yun Shen and Chuan-Feng Chen Chemical Reviews Article ASAP doi:10.1021/cr200087r
4. ↑ Diels–Alder Additions of Benzynes within Helicene Skeletons David Zhigang Wang, Thomas J. Katz, James Golen, and Arnold L. Rheingold J. Org. Chem.; 2004; 69(22) pp 7769–7771 doi:10.1021/jo048707h
5. ↑ One hundred years of helicene chemistry. Part 1: non-stereoselective syntheses of carbohelicenes Marc Gingras Chem. Soc. Rev., 2013,42, 968-1006 doi:10.1039/C2CS35154D
6. ↑ One hundred years of helicene chemistry. Part 2: stereoselective syntheses and chiral separations of carbohelicenes Marc Gingras, Guy Félix and Romain Peresutti Chem. Soc. Rev., 2013,42, 1007-1050 doi:10.1039/C2CS35111K
7. ↑ One hundred years of helicene chemistry. Part 3: applications and properties of carbohelicenes Marc Gingras Chem. Soc. Rev., 2013,42, 1051-1095 doi:10.1039/C2CS35134J
8. ↑ Recent Development of Helicene Synthesis Ken Kamikawa Journal of Synthetic Organic Chemistry, Japan Vol. 72 (2014) No. 1 p. 58-67 doi:10.5059/yukigoseikyokaishi.72.58
9. ↑ Freixas, Victor M.; Rouxel, Jérémy R.; Nam, Yeonsig; Tretiak, Sergei; Govind, Niranjan; Mukamel, Shaul (2023). "X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization". J. Am. Chem. Soc. 145 (38): 21012–21019. doi:10.1021/jacs.3c07032.
10. ↑ Meisenheimer, J. and Witte, K. (1903), Reduction von 2-Nitronaphtalin. Berichte der deutschen chemischen Gesellschaft, 36: 4153–4164. doi:10.1002/cber.19030360481
11. ↑ Synthese der isomeren Kohlenwasserstoffe 1, 2–5, 6-Dibenzanthracen und 3, 4–5, 6-Dibenzphenanthren Richard Weitzenböck and Albert Klingler Monatshefte für Chemie / Chemical Monthly Volume 39, Number 5, 315–323, doi:10.1007/BF01524529
12. ↑ A new reagent for resolution by complex formation; the resolution of phenanthro-[3,4-c]phenanthrene Melvin S. Newman, Wilson B. Lutz, and Daniel Lednicer Journal of the American Chemical Society 1955 77 (12), 3420–3421 doi:10.1021/ja01617a097
13. ↑ The Synthesis and Resolution of Hexahelicene Melvin S. Newman and Daniel Lednicer Journal of the American Chemical Society 1956 78 (18), 4765–4770 doi:10.1021/ja01599a060
14. ↑ Preparation of Helicenes through Olefin Metathesis  Shawn K. Collins, Alain Grandbois, Martin P. Vachon, Julie Côté Angewandte Chemie International Edition Volume 45, Issue 18 , Pages 2923–2926 2006 doi:10.1002/anie.200504150
15. ↑ Synthesis of Hexahelicene and 1-Methoxyhexahelicene via Cycloisomerization of Biphenylyl-Naphthalene Derivatives. Storch J., Sýkora J., Čermák J., Karban J., Císařová I., Růžička A. J. Org. Chem. 2009, 74, 3090. doi:10.1021/jo900077j
16. ↑ Helquat Dyes: Helicene-like Push–Pull Systems with Large Second-Order Nonlinear Optical Responses Benjamin J. Coe, Daniela Rusanova, Vishwas D. Joshi, Sergio Sánchez, Jan Vávra, Dushant Khobragade, Lukáš Severa, Ivana Císařová, David Šaman, Radek Pohl, Koen Clays, Griet Depotter, Bruce S. Brunschwig, and Filip Teplý The Journal of Organic Chemistry 2016 81 (5), 1912-1920 doi:10.1021/acs.joc.5b02692
17. ↑ Synthetic Control of the Excited-State Dynamics and Circularly Polarized Luminescence of Fluorescent “Push–Pull” Tetrathia[9]helicenes Y. Yamamoto, H. Sakai, J. Yuasa, Y. Araki, T. Wada, T. Sakanoue, T. Takenobu, T. Kawai, T. Hasobe, Chem. Eur. J. 2016, 22, 4263. doi:10.1002/chem.201504048
18. ↑ Controlled Excited-State Dynamics and Enhanced Fluorescence Property of Tetrasulfone[9]helicene by a Simple Synthetic Process Yuki Yamamoto, Hayato Sakai, Junpei Yuasa, Yasuyuki Araki, Takehiko Wada, Tomo Sakanoue, Taishi Takenobu, Tsuyoshi Kawai, and Taku Hasobe The Journal of Physical Chemistry C 2016 120 (13), 7421-7427 doi:10.1021/acs.jpcc.6b01123
19. ↑ Tetrathia[7]helicene Phosphorus Derivatives: Experimental and Theoretical Investigations of Electronic Properties, and Preliminary Applications as Organocatalysts D. Dova, L. Viglianti, P. R. Mussini, S. Prager, A. Dreuw, A. Voituriez, E. Licandro, S. Cauteruccio, Asian J. Org. Chem. 2016, 5, 537. doi:10.1002/ajoc.201600025
20. ↑ Synthesis and Structural Features of Quadruple Helicenes: Highly Distorted π Systems Enabled by Accumulation of Helical Repulsions Takao Fujikawa, Yasutomo Segawa, and Kenichiro Itami Journal of the American Chemical Society 2016 138 (10), 3587-3595 doi:10.1021/jacs.6b01303
21. ↑ Inherently Chiral Azonia[6]helicene-Modified β-Cyclodextrin: Synthesis, Characterization, and Chirality Sensing of Underivatized Amino Acids in Water Qinfei Huang, Liangwei Jiang, Wenting Liang, Jianchang Gui, Dingguo Xu, Wanhua Wu, Yoshito Nakai, Masaki Nishijima, Gaku Fukuhara, Tadashi Mori, Yoshihisa Inoue, and Cheng Yang The Journal of Organic Chemistry 2016 81 (8), 3430-3434 doi:10.1021/acs.joc.6b00130
22. ↑ Electrochemical Capacitive K+ EMIS Chemical Sensor Based on the Dibromoaza[7]helicene as an Ionophore for Potassium Ions Detection M. Tounsi, M. BenBraiek, A. Baraket, M. Lee, N. Zine, M. Zabala, J. Bausells, F. Aloui, B. BenHassine, A. Maaref, A. Errachid, Electroanalysis 2016, 28, 2892. doi:10.1002/elan.201600104
23. ↑ Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion Ying Wang, Hui Zhang, Maren Pink, Arnon Olankitwanit, Suchada Rajca, and Andrzej Rajca Journal of the American Chemical Society 2016 138 (23), 7298-7304 doi:10.1021/jacs.6b01498
24. ↑ Synthesis and study of the structural properties of oxa[5]helicene derivatives M. Shyam Sundara, Sibaprasad Sahoob, Ashutosh V. Bedekara, Tetrahedron: Asymmetry Volume 27, Issue 16, 1 September 2016, Pages 777–781 doi:10.1016/j.tetasy.2016.06.020
25. ↑ Synthesis and Photophysical Properties of Aza[n]helicenes Gourav M. Upadhyay, Harish R. Talele, and Ashutosh V. Bedekar The Journal of Organic Chemistry 2016 81 (17), 7751-7759 doi: 10.1021/acs.joc.6b01395
26. ↑ Sultam-Based Hetero[5]helicene: Synthesis, Structure, and Crystallization-Induced Emission Enhancement. Tarunpreet S. Virk, Niranjan V. Ilawe, Guoxian Zhang, Craig P. Yu, Bryan M. Wong, Julian M. W. Chan. ACS Omega 2016; 1(6), 1336–1342 doi:10.1021/acsomega.6b00335

General references

* Chuan-Feng; Yun Shen (2017). Helicene Chemistry: From Synthesis to Applications. Springer. doi:10.1007/978-3-662-53168-6. ISBN 978-3-662-53168-6.

* v
* t
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Polycyclic aromatic hydrocarbons

2 rings|

* Butalene
* Azulene
* Naphthalene

3 rings|

* Acenaphthene
* Acenaphthylene
* Anthracene
* Fluorene
* Phenalene
* Phenanthrene

4 rings|

* Benz[a]anthracene
* Benzo[a]fluorene
* Benzo[c]fluorene
* Benzo[c]phenanthrene
* Chrysene
* Fluoranthene
* Pyrene
* Tetracene
* Triphenylene
* Tricyclobutabenzene

5 rings|

* Benz[e]acephenanthrylene
* Benzopyrene
* Benzo[a]pyrene
* Benzo[e]pyrene
* Benzo[a]fluoranthene
* Benzo[b]fluoranthene
* Benzo[j]fluoranthene
* Benzo[k]fluoranthene
* trans-Bicalicene
* Dibenz[a,h]anthracene
* Dibenz[a,j]anthracene
* Olympicene
* Pentacene
* Perylene
* Picene
* Tetraphenylene

6+ rings|

* Anthanthrene
* Benzo[ghi]perylene
* Circulene
* Corannulene
* Coronene
* Dicoronylene
* Diindenoperylene
* Heptacene
* Hexacene
* Kekulene
* Ovalene
* Zethrene

General classes|

* Acene
* Helicene
* Phenacene

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