Visible-light-mediated metal-free regioselective oxidative C–C bond cleavage of lignin dimers to aromatic acids

Abstract

The upgrading of lignin is a sustainable and promising pathway for fossil-based aromatic compounds but always faces low selectivity. Herein, a metal-free photocatalyst, 2,4,6-triphenylpyrylium tetrafluoroborate (TPP), was illustrated to remarkably facilitate the regioselective oxidative C_α–C_β bond cleavage of β-1 and β-O-4 lignin alcohol/ketone models into aromatic acids (92–99% yields) under visible-light irradiation at room temperature without any additive/co-catalyst, which was enabled by the synergistic effect of C_β–H⋯C(TPP) interaction and·˙O₂⁻/¹O₂ species. The synergy of the catalyst–substrate interaction and active species offers a reference for the enhancive and selective transformation of polymeric biomass and complex molecules.