Bent out of shape

I got acquainted with Professor Jasti on a recent trip to Boston University. His lab is pushing the frontiers of cycloparaphenylenes (CPP’s), which are warped carbon-rich molecules that are not only aesthetically pleasing, but might one day act as useful precursors to carbon nanotubes and a myriad other applications (some are yet-to-be identified). Previously, the Jasti lab reported their synthesis of [6] and [7] CPP’s. Many of you know that Professor Itami of Nagoya University, Japan, has also been quite active in this area. The latest contribution from the Jasti lab deals with the [5]CPP nanohoop fragment of buckminsterfullerene. The remarkable room-temperature synthesis of this molecule was reported in Nature Chemistry not long ago. The target molecule forms brilliant-red needles and has been characterized by a range of spectroscopic methods. The compound is soluble in many organic solvents and is highly strained, which is not surprising considering how warped the rings are (the strain energy of [5]CPP is 119 kcal/mol…). The proton NMR of the newly minted member of the [5]CPP class of compounds showcases only one singlet at 7.68 ppm, which means that there are no rotational isomers at room temperature. The synthesis takes only 3 steps and I encourage you to take a look at it (not surprisingly, the Suzuki coupling features prominently in this approach). I am showing only the final step that leads to the formation of the target molecule. For me, the most intriguing aspect of this paper is the extent to which chemists can push the concept of aromaticity. I consider it quite fascinating that aryl rings can get bent out of shape in such a dramatic fashion, while retaining their core aromatic character.


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