Gas phase synthesis of [4]-helicene

Authors

Long Zhao, University of Hawaii, Manoa
Ralf I. Kaiser, University of Hawai'i, Manoa
Bo Xu, Lawrence Berkeley National Laboratory
Utuq Ablikim, Lawrence Berkeley National Laboratory
Wenchao Lu, Lawrence Berkeley National Laboratory
Musahid Ahmed, Lawrence Berkeley National Laboratory
Mikhail M. Evseev, Samara National Research University
Eugene K. Bashkirov, Samara National Research University
Valeriy N. Azyazov, Samara National Research University
Marsel V. Zagidullin, Samara National Research University
Alexander N. Morozov, Department of Chemistry and Biochemistry, Florida International University
A. Hasan Howlader, Department of Chemistry and Biochemistry, Florida International University
Stanislaw F. Wnuk, Department of Chemistry and Biochemistry, Florida International UniversityFollow
Alexander M. Mebel, Samara National Research University; Department of Chemistry and Biochemistry, Florida International University
Dharati Joshi, University of California - Berkeley
Gregory Veber, University of California - Berkeley
Felix R. Fischer, University of California - Berkeley

Date of this Version

4-3-2019

Document Type

Article

Abstract

A synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry involving elementary reactions with aryl radicals is presented. In contrast to traditional synthetic routes involving solution chemistry and ionic reaction intermediates, the gas phase synthesis involves a targeted ring annulation involving free radical intermediates. Exploiting the simplest helicene as a benchmark, we show that the gas phase reaction of the 4-phenanthrenyl radical ([C14H9]•) with vinylacetylene (C4H4) yields [4]-helicene (C18H12) along with atomic hydrogen via a low-barrier mechanism through a resonance-stabilized free radical intermediate (C18H13). This pathway may represent a versatile mechanism to build up even more complex polycyclic aromatic hydrocarbons such as [5]- and [6]-helicene via stepwise ring annulation through bimolecular gas phase reactions in circumstellar envelopes of carbon-rich stars, whereas secondary reactions involving hydrogen atom assisted isomerization of thermodynamically less stable isomers of [4]-helicene might be important in combustion flames as well.

Comments

Originally published in Nature Communications.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 License.

Recommended Citation

Zhao, Long; Kaiser, Ralf I.; Xu, Bo; Ablikim, Utuq; Lu, Wenchao; Ahmed, Musahid; Evseev, Mikhail M.; Bashkirov, Eugene K.; Azyazov, Valeriy N.; Zagidullin, Marsel V.; Morozov, Alexander N.; Howlader, A. Hasan; Wnuk, Stanislaw F.; Mebel, Alexander M.; Joshi, Dharati; Veber, Gregory; and Fischer, Felix R., "Gas phase synthesis of [4]-helicene" (2019). Department of Chemistry and Biochemistry. 56.
https://digitalcommons.fiu.edu/chemistry_fac/56