Refining lignin into bioactive 2,6-diphenylpyridines via amine-participated [4 + 2] condensation strategy

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Nitrogen-participated catalytic conversion of lignin into N-containing aromatic compounds has gained much attention to meet the requirements of value-added biorefinery. Hence, a KOH-promoted [4 + 2] condensation strategy was developed for direct synthesis of bioactive 2,6-diphenylpyridines from lignin β-O-4 motifs and real biomass feedstocks using 3-amino-3-phenyl-propanol under mild conditions. This cascade transformation includes an integrated sequence of coupled self-hydrogen-transfer C-O bonds cleavage, aldol condensation, dehydrogenation, C-N bonds generation and dehydration together with construction of N-heterocyclics, as corroborated by experimental study and DFT calculation. Interestingly, the bioactive 2-methoxy-4-(6-phenylpyridin-2-yl)phenol, an excellent antibacterial efficacy against Bacillus subtilis ( B. subtilis ) was obtained from poplar woody biomass based on this protocol, showcasing the possible applications of the 2,6-diphenylpyridines products in pharmaceutical field. This transformation offers a sustainable route to value-added aromatic heterocyclic chemicals beyond petroleum route. A [4 + 2] condensation strategy for the conversion of lignin β-O-4 models into 2,6-diphenylpyridine derivatives is presented. With this protocol, the value-added broad-spectrum antimicrobial and antifungal bioactive 2,6-diphenylpyridine derivatives have been obtained from poplar wood. • 2,6-diphenylpyridines were produced from lignin and β-O-4 model compounds. • The transformation features mild condition, free of metal catalyst and oxidant. • The reaction follows a highly coupled multi-step pathway to form N-heterocyclics. • A broad-spectrum antibacterial compound was obtained from poplar powder.