Pd-catalyzed synthesis of 9,9'-bifluorenylidene derivatives via dual C-H activation of bis-biaryl alkynes.

We report a novel Pd-catalyzed alkyne-directed dual C-H activation of bis-biaryl alkynes, which produced important and useful products, 9,9'-bifluorenylidene (9,9'BF) derivatives, in high yields with a broad range of functional group compatibility. The combination of the PdCl2 catalyst with the MnO2 oxidant and PivOH additive is vital for realization of the present catalytic transformation. Mechanistic evidence suggests that this intramolecular arene/alkyne annulation may take place through unusual dual C-H activation followed by annulation with alkynes.