One‐Shot Pd(II)‐Catalyzed Multiple C–H Activation Enables Modular Construction of Fluorenylidene Oxindole‐Based Multi(Polycyclic) Aromatic Enes

ABSTRACT

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 PdCl ₂ /PivOH/MnO ₂ 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.