Dithieno[3,4‑b:3′,4′‑d]thiophene-Annelated Antiaromatic Planar Cyclooctatetraene with Olefinic Protons

The design and synthesis of a new planar cyclooctatetraene (COT) with protons directly connected to the COT ring was attained by monoannelation with dithieno[3,4-b:3′,4′-d]thiophene. The planar structure of the COT core was unambiguously confirmed by X-ray crystallography. The magnetic antiaromaticity of the COT core was found to be higher than that of the previously synthesized planar COTs with olefinic protons, according to the results of 1H NMR and absorption spectra as well as NICS calculations.