Polygons: [8]Circulenes were easily prepared by Pd-catalyzed annulations of tetraiodotetraphenylenes with alkynes. Their saddle-shaped structure with an [8]radialene character was identified by X-ray crystallography. Similar to 1,3,5,7-cyclooctatetraene, they have a tub-shaped eight-membered ring, but all of the bond lengths and bond angles are almost equal. Variable-temperature NMR investigations showed interesting dynamic behavior.
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Feng et al. (2013) studied this question.
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