Hydrogen-Bonding-Promoted Cascade Rearrangement Involving the Enlargement of Two Rings: Efficient Access to Polycyclic Quinoline Derivatives
Wen-Bin Cao1+, Shijun Li3+, Meng-Meng Xu1, Haiyan Li2, Xiao-Ping Xu1,*（徐小平）, Yu Lan3,4,*（蓝宇）, and Shun-Jun Ji1,*（纪顺俊）
1Key Laboratory of Organic Synthesis of Jiangsu Province，College of Chemistry, Chemical Engineering and Materials Science & Collaborative Innovation Center of Suzhou Nano Science and Technology，Soochow University, Suzhou 215123 (China)
2Analysis and Testing Center, Soochow University，Suzhou 215123 (China)
3College of Chemistry, and Institute of Green Catalysis，Zhengzhou University, Zhengzhou, Henan 450001 (China)
4School of Chemistry and Chemical Engineering，Chongqing University, Chongqing 400030 (China)
+These authors contributed equally to this work.
Angew. Chem. Int. Ed.2020, 59, 21425--21430
An efficient cascade reaction of tryptamine‐derived isocyanides with C,N‐cyclic azomethine imines is described. The polycyclic pyrrolo[2,3‐c]quinoline derivatives, which benefited from rearrangement process driven by hydrogen bonding, could be directly assembled in moderate to good yields (40–87 %) under metal‐free and mild conditions. This transformation involved four new heterocyclic rings formations and uniquely, ring opening of indole as well as ring expansion of C,N‐cyclic azomethine imine. Both experimental and DFT studies provided guidance on the in‐depth insight into the reaction pathways and hydrogen bonding was identified to lower the free energy barrier in transition states. This work constitutes a rare example of tryptamine‐derived isocyanide‐based cascade reactions, and potentially could be a powerful synthetic strategy for accessing polycyclic analogues involved in natural products.