Exploring the chemistry of a double-stranded cycle with the carbon skeleton of the belt region of the C₈₄ fullerene

Intense scale-up efforts greatly improved the availability of the known double-stranded cycle 2 with two bridging ether units. The chemistry of 2 towards Bronsted and Lewis acids could, therefore, be investigated quite comprehensively. It was discovered that the reactivity of 2, whose carbon framework resembles the belt region of the C₈₄ (D₂) fullerene, is rather unusual as compared with acyclic model compounds. Whereas the latter could easily be dehydrated to the corresponding planar arenes, the former gave rise to a bouquet of unexpected reactions, which all avoided the aromatization of 2 to its still-elusive, fully conjugated congener B. Intermediates generated from 2 under acidic conditions attack the solvent (e.g. toluene) to give 4, form bridging lactones to give 11 or close back to starting material 2 (e.g. from 16) rather than dehydrate to more highly conjugated structures on the way to the fully unsaturated target cycle B. The structure of compound 4 was solved by X-ray diffraction. Through the reactions of 2 with Lewis acids, derivatives 14 and 15 became accessible. They are candidates for future attempts to achieve the desired aromatization under basic conditions or by thermal treatment.