Lignin, the heterogeneous aromatic macromolecule found in the cell walls of vascular plants, is an abundant feedstock for the production of biochemicals and biofuels. Many valorization schemes rely on lignin depolymerization, with decades of research focused on accessing monomers through C–O bond cleavage, given the abundance of β–O–4 bonds in lignin and the large number of available C–O bond cleavage strategies. Monomer yields are, however, invariably lower than desired, owing to the presence of recalcitrant C–C bonds whose selective cleavage remains a major challenge in catalysis. In this Review, we highlight lignin C–C cleavage reactions, including those of linkages arising from biosynthesis (β–1, β–5, β–β and 5–5) and industrial processing (5–CH₂–5 and α–5). We examine multiple approaches to C–C cleavage, including homogeneous and heterogeneous catalysis, photocatalysis and biocatalysis, to identify promising strategies for further research and provide guidelines for definitive measurements of lignin C–C bond cleavage.

木质素是在维管植物细胞壁中发现的异质芳香族大分子，是生产生化试剂和生物燃料的丰富原料。鉴于木质素中 β-O-4 键的丰富性和大量可用的 C-O 键裂解策略，许多增值方案依赖于木质素解聚，几十年的研究集中在通过 C-O 键裂解获得单体。然而，由于存在顽固的 C-C 键，单体产率总是低于预期，其选择性裂解仍然是催化中的主要挑战。在这篇综述中，我们重点介绍了木质素 C-C 切割反应，包括由生物合成 （β-1、β-5、β-β 和 5-5） 和工业加工 （5-CH_2-5 和 α-5） 产生的键反应。我们研究了 C-C 切割的多种方法，包括均相和非均相催化、光催化和生物催化，以确定进一步研究的有前途的策略，并为木质素 C-C 键切割的明确测量提供指南。