Lignin is a complex and amorphous aromatic polymer, and its depolymerization reaction mechanism is still not fully understood. The study of this mechanism is challenging due to the difficulties in characterizing lignin. However, the β-O-4 linkage is the most common type, making up 45-75% of the total linkages in native lignin [Renew. Sustain. Energy Rev. 2019, 107, 232–249]. This research has developed synthetic internal and terminal β-O-4 model compounds, including isotopically labelled versions, to investigate key intermediates in lignin polymerization. These studies aim to study the reactivity of different linkages and develop methods to convert biomass into valuable products.