Oxidation of a Dithieno[3,4‐b:3′,4′‐d]thiophene Cyclic Dimer Containing a Planar Cyclooctatetraene Ring: Retention of High Antiaromaticity During Reactions

One‐electron and peracid oxidations of dithieno[3,4‐b : 3’,4’‐d]thiophene cyclic dimer, which contains an antiaromatic planar cyclooctatetraene (COT) core, were conducted. The reaction of the cyclic dimer with SbCl5 produced isolable radical cation salts. Density functional theory (DFT) calculations showed that the spin density of the radical cation resides not on the COT ring but on the peripheral sulfur and carbon atoms in the thiophene unit with retention of high antiaromaticity based on the nucleus‐independent chemical shift (NICS). The peracid oxidation of the cyclic dimer was found to proceed not on the COT ring but on the bridging sulfur atom in the dithienothiophene moiety. The retention of the high antiaromaticity of the COT ring after the sulfoxide formation was experimentally confirmed based on the relative hardness, and also was theoretically supported by NICS calculations. Interestingly, the DFT calculations suggested that the high antiaromaticity does not enhance the reactivity towards the epoxidation on the COT ring. Antiaromaticity is not lost: One‐electron and peracid oxidations of dithieno[3,4‐b : 3′,4′‐d]thiophene cyclic dimer bearing a high antiaromatic COT core gave the corresponding radical cation and monosulfoxide at the bridging part, respectively. Retentions of the high antiaromaticity after the oxidation reactions were shown theoretically and/or experimentally. The unique reactivity is in contrast to a general notion that antiaromatic compounds are highly unstable and extremely reactive