Cu-Catalyzed Funneling Oxidation Enables C–C Bond Cleavage in Lignin-derived Compounds

Abstract

Abstract The structural complexity and chemical heterogeneity of lignin present a formidable barrier to its use as a sustainable replacement for petroleum-derived aromatics. Here, we report a robust, earth-abundant copper/nitroxyl catalytic system that achieves the aerobic oxidative funneling of crude, non-pre-fractionated reductive catalytic fractionation (RCF) lignin oil into a single, high-value platform chemical: 2,6-dialkoxybenzoquinone. This transformation operates via a cooperative proton-coupled electron transfer (PCET) mechanism to cleave robust aromatic–aliphatic C–C bonds under mild aerobic conditions (O2 or open air). Using various alcohols as both solvent and nucleophile, the reaction provides modular access to a library of 2,6-dialkoxybenzoquinones in up to 86% isolated yield from model monomers/dimers and an impressive 27 wt % yield (gram product per gram lignin) directly from high-S poplar wood lignin oil (62 mol % convergent yield based on the S-phenol equivalents in the lignin oil). Crucially, we demonstrate that these tunable biomass-derived quinones serve as highly versatile synthons for advanced chemical synthesis to access precursors of bioactive natural product (scutellarein), organic electronics (TCNQ-type acceptors), platform building blocks (1,4-cyclohexanediol), cross-coupling reactions, and a modified high-performancepolyether ether ketone (PEEK) polymer. This work establishes a bridge connecting raw biomass fractionation to diverse applications in synthetic chemistry and materials science.