Successive Cleavage and Reconstruction of Lignin β‐O‐4 Models and Polymer to Access Quinoxalines
Yuxuan Liu, Qi Luo, Qiang Qian, Hua Wang, Yangming Ding, Chao Wang, Jianliang Xiao, Changzhi Li, Tao Zhang
Abstract
Abstract The construction of N‐heterocyclic compounds from lignin remains a great challenge due to the complex lignin structure and the involvement of multiple steps, including the cleavage of lignin C−O linkages and the formation of heterocyclic aromatic rings. Herein, the first example of KOH mediated sustainable synthesis of quinoxaline derivatives from lignin β‐O‐4 model compounds in a one‐pot fashion under transition‐metal‐free conditions has been achieved. Mechanistic studies suggested that this transformation includes highly coupled cascade steps of cleavage of C−O bonds, dehydrative condensation, sp 3 C−H bond oxidative activation, and intramolecular dehydrative coupling reaction. With this protocol, a wide range of functionalized quinoxalines, including an important drug compound AG1295, were synthesized from lignin β‐O‐4 model compounds and β‐O‐4 polymer, showcasing the application potential of lignin in pharmaceutical synthesis.