Synthesis of Partially Hydrogenated Cycloparaphenylenes with Bent and Fused Structures Bearing Armchair Carbon Nanotube-like Connections

The Diels–Alder reactions
between 2 equiv of (E,E)-1,4-bis­(4-bromophenyl)-1,3-butadiene
and 1,4-benzoquinone
led to the formation of a key intermediate with all four 4-bromophenyl
substituents cis to one another. The subsequent nickel-mediated
homocoupling reactions then produced partially hydrogenated cycloparaphenylenes,
including a molecule bearing two units of tetrahydro[6]­cycloparaphenylene
(4H[6]­CPP) fused together through two 1,4-dimethoxybenzene units in
an armchair (6,6)carbon nanotube-like connection. Similarly, two 6H[9]­CPPs
were connected through three 1,4-dimethoxybenzene units in an armchair
(9,9)carbon nanotube-like arrangement. A bent 8H[12]­CPP and a bent
12H[18]­CPP, which were fused intramolecularly with two and three 1,4-dimethoxybenzene
units, respectively, to create the bent structures, were likewise
synthesized. A molecule containing a bent 8H[12]­CPP fused to a 4H[6]­CPP
was likewise constructed. The structures of these partially hydrogenated
CPPs were established by X-ray structure analysis, NMR spectroscopy,
and additional independent synthetic pathways.