Polyarylquinone Synthesis by Relayed Dehydrogenative [2 + 2 + 2] Cycloaddition

Polyarylquinones have found a lot of applications in optoelectronics, photocatalysis, bioimaging, and pharmaceutically relevant materials. However, their synthesis is often challenging and plagued with various bottleneck steps. Here, we demonstrate a relayed addition of fulvene moieties onto quinones. The developed ligand-assisted Pd-catalyzed dehydrogenative [2 + 2 + 2] cycloaddition reaction enables facile access to a new class of polyarylquinones. The key to achieving a high regioselectivity is the precisely controlled addition of the two fulvene units to the quinone conferred by the Pd catalyst. The work also establishes the broad substrate scope of the reaction and delves into the mechanism of the dehydrogenative coupling reaction. Moreover, single-crystal X-ray diffraction reveals interesting packing motifs suggesting the suitability of these materials in optoelectronics. As a practical utilization of the reaction, various synthesized polyarylquinones with structural diversity were screened for their redox properties and found to exhibit better antioxidant or chemotherapeutic properties.