10.1021/ja801918n
The research aims to synthesize [6.8]3cyclacene, a unique type of carbon nanotube model. The study addresses the challenges of bending a linear chain of benzene rings into a hoop shape and overcoming the high reactivity due to a small singlet-triplet gap. The researchers used 4,6-dimethylisophthalaldehyde as the starting material, selectively reduced one aldehyde group with NaBH4, and converted it to a bromide. This was followed by a Wittig cyclization to form a cyclic intermediate. Key steps included bromination with NBS, oxidation with IBX, and a final McMurry coupling using low-valent titanium to achieve the [6.8]3cyclacene. The synthesized compound exhibited a D3h symmetrical structure, confirmed by analytical data and X-ray measurements. The study concludes that [6.8]3cyclacene represents the smallest and most strained member of the [6.8]n series, with about 31% conjugation around its torus. This work provides a general route to synthesize larger [6.8]ncyclacenes, which are expected to have less strain and stronger conjugation, potentially leading to new types of carbon nanotubes.
