A novel tandem single-electron oxidative ring expansion reaction has been developed for the construction of the saddle-shaped polycyclic arenes fused with cyclooctatetraene, that is, dibenzo [3,4:7,8]cycloocta[1,2-l]phenanthrenes (dbCOTPs). The combination of Cu(OTf) 2 catalyst with DDQ triggered the selective oxidation of o-biphenyl-tethered methylenecirculenes fused with a seven-membered ring, giving rise to the formation of the corresponding eight-membered ring fused dbCOTPs. The present tandem ring expansion of a seven-to an eight-membered ring takes place via the selective single-electron oxidation of the benzylidene moiety, intramolecular spirocyclization, and 1,2-aryl migration sequence.

A strategy for amide C–N bond activation with ruthenium catalyst is described for the first time. The in situ formed bis-cycloruthenated complexes were demonstrated to be the key active species with superior oxidative addition ability to an inert amide C–N bond. The direct C–H bond activation of 2-arylpyridines followed by the amide C–N bond activation took place in the presence of a ruthenium precatalyst to produce monoacylation products in moderate to good yields. Synthetically useful functional groups, such as halogen atoms (F and Cl), ester, acetyl, and vinyl, remained intact during tandem C–H/C–N bond activation reactions.