Cumulenes, i.e., hydrocarbons with three or more consecutive double bonds, and hexaphenylbenzene (HPB) can be used as building blocks for carbon allotropes with sp- and sp2-hybridized carbon, respectively. Derivatives of both cumulenes and hexaphenylbenzene have been independently studied for use in molecular devices. Combining both of these types of carbon-rich molecules in a single compound is an interesting research target.
Rik R. Tykwinski, University of Alberta, Edmonton, Canada, and colleagues have developed a method for the functionalization of hexaphenylbenzene using a Friedel–Crafts acylation, selectively providing monoacylated products (pictured below). The monoacylated products can then be used for the synthesis of cumulenes.
The team found that the cumulene with both HPB and alkynyl end groups shows a surprisingly high kinetic stability due to the bulky nature of the HPB moiety—despite the presence of alkynyl end groups, which are known to reduce stability. Furthermore, this cumulene features a low barrier to rotation, leading to facile cis/trans isomerization at about room temperature. This stable cumulene might be a useful building block for larger, carbon-rich molecules.
- Acylation of Hexaphenylbenzene for the Synthesis of Cumulenes,
Matthew A. Johnson, Max Martin, Kévin Cocq, Michael Ferguson, Norbert Jux, Rik R. Tykwinski,
Eur. J. Org. Chem. 2022.