It was already speculated in 2011 that nanobelts (aka nanorings) as featured in this blog could pave the way to a bottom-up approach to nanotubes. Well, consider it done. The way is paved. Haruka Omachi et al describe here how to produce nanotubes just like that, but in a slightly different way we had anticipated.
Synthesis started from 12-cycloparaphenylene (12-CPP) which incidentally is commercially available (guys! smallest wedding ring ever!). Heating the compound in ethanol at 500°C on a sapphire surface apparently does the trick. Due to experimental set-up constraints the experimental yield was only 5 microgram which is the lowest this blog has ever witnessed for any reported reaction. Does this still count as preparative chemistry?
The windows of opportunity are small: below 500°C nothing happens and above 650°C the lot vaporises. Success also depends critically on surface orientation of the sapphire substrate. Acetylene gas instead of ethanol did not work.
The diameter of the nanotubes match that of the nanorings. What is conspicuously absent from the article is an estimate for the nanotube length.