It is shown that dilithiation of HBT using nBuLi allows reaction with 1 to proceed, followed by the addition of trifluoroacetic acid to promote intramolecular ring closure via a Friedel–Crafts reaction, forming 2 in 30% yield. To synthesize the spiro-HSE compounds (where X = S or Se), dichalcogenide units must first be introduced at the bay regions of 2 using nBuLi and either S or Se powder, before these 6-membered rings are subsequently contracted to form the monochalcogenide species 3 using Cu nano powder. By contrast, the synthesis of 3 (where X = Te) can be accomplished in one step using nBuLi and Te powder, without forming the dichalcogenide. The product compounds 3 all exhibit bowl-shaped conformations, as confirmed using computational calculations and X-ray crystallography, and are thermally stable up to around 300 °C.Adding AgSbF6 to 3 (where X = Se) forms the radical cation salt, giving the spiro-HSE a charge of +1. Intriguingly, it is found that the bowl-depths of the two segments of the radical cation are 0.48 Å and 0.28 Å, in contrast to the bowl-depths of the two segments of the non-radical cation structure, which are 0.65 Å and 0.72 Å. This shows that the charge in the radical cation salt is not equally distributed over the two bowls, which is attributed to the Jahn–Teller effect.
