Metal-free access to β-carbolines via single-electron transfer catalyzed by a triaryl carbenium ion pair

• Main Authors: Zhang, Zhenguo, Gu, Jun, Lv, Yongheng, Ji, Liang, Liu, Xiaoxiao, Wu, Beishen, Liu, Fang, Jia, Zhenhua, Loh, Teck-Peng
• Other Authors: School of Chemistry, Chemical Engineering and Biotechnology
• Format: Article
• Language: English
• Published: 2023
• Subjects: Science::Chemistry; Ion Pair; Single-Electron Transfer
• Online Access: https://hdl.handle.net/10356/168719
• Institution: Nanyang Technological University

The β-carboline moiety exists in a wide range of drugs and natural products, but synthesis often relies on noble metals and stochiometric oxidants. Here, we develop a metal-free strategy using a triaryl carbenium ion pair as a catalyst to access β-carbolines from tryptamines and aromatic aldehydes. This protocol exhibits excellent functional group tolerance, and its practicality is demonstrated with the preparation of Eudistomin U and fluorescent compounds on gram scales. Mechanistic studies reveal that the trityl radical is generated via a single-electron transfer process and subsequently trapped by an oxygen molecule. In addition, the in-situ-generated reactive oxygen-centered radical is also found to be essential for the efficient dehydroaromatization process to afford the desired products.