Tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene: A Potential Tetraradicaloid Hydrocarbon

A tetramesityl derivative of hitherto unknown tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), which is a potential tetraradicaloid hydrocarbon, was synthesized. Theoretical calculations based on spin‐flip time‐dependent density functional theory predict that the closed‐shell D2h form of TCPTP is more stable than the open‐shell D4h form with its slightly tetraradical character. The tetramesityl derivative (Mes)4‐TCPTP exhibits remarkable antiaromaticity as a result of the peripheral 20‐π‐electron circuit, which causes an absorption maximum at a long wavelength and a small HOMO–LUMO gap. In solution, (Mes)4‐TCPTP most likely adopts rapidly equilibrating D2h structures that interconvert via the D4h transition state. X‐ray crystallographic analysis showed (Mes)4‐TCPTP as an approximate D2h structure. Aromatic? A tetramesityl derivative of hitherto unknown tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene, a potential tetraradicaloid hydrocarbon, was synthesized. It exhibits remarkable antiaromaticity as a result of the peripheral 20‐π‐electron circuit. In solution, it adopts closed‐shell D2h structures that rapidly equilibrate via the D4h structure, and in crystals, it adopts an approximate D2h structure.