One-Shot Pd(II)-Catalyzed Multiple C-H Activation Enables Modular Construction of Fluorenylidene Oxindole-Based...

Multi(polycyclic) aromatic enes (MPAEs) are attractive π-architectures but their synthesis typically requires prefunctionalized, π-extended building blocks. Herein we report a one-shot Pd(II)-catalyzed multiple C-H activation strategy that enables modular access to fluorenylidene/oxindole-based MPAEs through intramolecular diarylation of N-aryl amide-tethered biarylalkynes. The synergistic PdCl₂/PivOH/MnO₂ system promotes sequential C-H activation/alkyne insertion/C-H activation under mild conditions, furnishing mono-, di-, and tri-olefin-bridged frameworks in good to high yields. Mechanistic investigations, including kinetic isotope effect measurements and DFT calculations, indicate that the syn-alkyne insertion step is likely rate-determining, whereas the C-H activation steps proceed through a pivalate-assisted concerted metalation-deprotonation (CMD) pathway. The method allows rapid assembly of densely conjugated, nonplanar π-systems from simple linear precursors, including multiple annulations that proceed in a single operation. The resulting 3D π-architectures display broad and bathochromically shifted absorptions (λ_onset up to 820 nm), tunable frontier orbital energies, and donor-acceptor electronic structures modulated by π-extension and heteroatom incorporation. This modular C-H activation platform provides efficient entry to structurally diverse, narrow optical gap MPAEs and expands the synthetic toolbox for advanced optoelectronic π-materials.