Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland.
Nat Commun. 2023 May 22;14(1):2830. doi: 10.1038/s41467-023-38534-1.
Efficient valorization of lignin, a sustainable source of functionalized aromatic products, would reduce dependence on fossil-derived feedstocks. Oxidative depolymerization is frequently applied to lignin to generate phenolic monomers. However, due to the instability of phenolic intermediates, repolymerization and dearylation reactions lead to low selectivity and product yields. Here, a highly efficient strategy to extract the aromatic monomers from lignin affording functionalized diaryl ethers using oxidative cross-coupling reactions is described, which overcomes the limitations of oxidative methods and affords high-value specialty chemicals. Reaction of phenylboronic acids with lignin converts the reactive phenolic intermediates into stable diaryl ether products in near-theoretical maximum yields (92% for beech lignin and 95% for poplar lignin based on the content of β-O-4 linkages). This strategy suppresses side reactions typically encountered in oxidative depolymerization reactions of lignin and provides a new approach for the direct transformation of lignin into valuable functionalized diaryl ethers, including key intermediates in pharmaceutical and natural product synthesis.
有效地利用木质素，这种可持续的功能性芳香产品资源，可以减少对化石衍生原料的依赖。氧化解聚通常用于木质素以生成酚类单体。然而，由于酚类中间体的不稳定性，重排和脱芳构化反应导致低选择性和产物收率。在这里，描述了一种从木质素中提取芳香单体的高效策略，该策略通过氧化交叉偶联反应生成功能性二芳基醚，克服了氧化方法的局限性，并提供了高价值的特种化学品。苯硼酸与木质素反应，将活性酚中间体转化为稳定的二芳基醚产物，近乎理论最大收率（基于β-O-4 键含量，山毛榉木质素为 92%，杨木木质素为 95%）。该策略抑制了木质素氧化解聚反应中常见的副反应，并为木质素直接转化为有价值的功能性二芳基醚提供了一种新方法，包括药物和天然产物合成中的关键中间体。
