Date of this Version
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 -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 - and -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 -helicene might be important in combustion flames as well.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
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 -helicene" (2019). Department of Chemistry and Biochemistry. 56.
In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).