C–H activation route to dibenzo[a,e]pentalenes: annulation of arylacetylenes promoted by PdCl2–AgOTf–o-chloranil

A novel catalytic C–H activation route to privileged dibenzo[a,e]pentalene (DBP) structures has been established. In the presence of PdCl2, AgOTf, and o-chloranil, a C–H/C–H annulation of arylacetylenes takes place to furnish the corresponding DBPs. A number of mechanistic experiments indicate that this new annulation occurs through alkyne-directed, ortho-selective, electrophilic aromatic C–H palladation. Not only symmetric diarylacetylenes but also unsymmetric arylacetylenes are applicable to this reaction. UV-vis absorption spectra and DFT studies on the resulting DBPs indicate a strong substituent effect on the energy levels of the HOMO and HOMO−1 of DBPs.