Katsuma Matsui, Masako Fushimi, Yasutomo Segawa, and Kenichiro Itami
Org. Lett. 2016, ASAP. DOI: 10.1021/acs.orglett.6b02702
Benzannulated cyclacenes (BCs) have been proposed as stable zigzag carbon nanobelts. Density functional theory (DFT) calculations revealed a closed-shell ground state for BC, whereas an open-shell ground state was suggested for cyclacene. The calculated strain energy and frontier molecular orbital energies of BC also implied high stability. An unstrained macrocycle 1, consisting of orthophenylene and ethynylene moieties, was designed as a potential precursor for BC and synthesized by sequential Suzuki–Miyaura cross-coupling of diphenylacetylene derivatives. While the conversion of 1 into BC is still under investigation, an unexpected rearrangement of the triene moieties in 1, affording a tribenzo[f,k,m]tetraphene structure, was discovered during the screening of reaction conditions. An attempt was made to rationalize this result by proposing a plausible reaction mechanism that proceeds via intermediates containing cyclobutadiene or Dewar benzene moieties. The proposed mechanism is partially supported by DFT calculations.