Synthesis of Benzothieno[60]fullerenes through Fullerenyl Cation Intermediates

Benzothieno[60]fullerenes were synthesized using fullerenyl cations as key intermediates. The reaction proceeded through a nucleophilic attack of the sulfur atom as a weak nucleophile to the fullerenyl cation electrophile. A monoarylated fullerene, (2-methylthiophenyl)hydro[60]fullerene, C₆₀ArH (Ar = C₆H₄-SMe-2 and so on; four derivatives) was subjected to deprotonation with KOtBu to form a fullerenyl anion ArC₆₀^-, followed by oxidation using I₂ to generate a fullerenyl cation ArC₆₀⁺, leading to intramolecular demethylative cyclization via fullerene cation-S interaction to the product. Electrochemical and computational studies revealed slightly narrower band gap of this compound than usual fullerene derivatives because of the relatively high-lying HOMO of the fused thieno moiety.