Enantioselective Radical Cyclization of Tryptamines by Visible Light-Excited Nitroxides
By: Kangjiang Liang, Xiaogang Tong, Tao Li, Bingfei Shi, Haiyang Wang, Pengcheng Yan , and Chengfeng Xia*
Key Laboratory of Medicinal Chemistry for Natural Resource (Ministry of Education and Yunnan Province), School of Chemical Science and Technology, Yunnan University, Kunming 650091, China
State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650201, China
School of Pharmaceutical Sciences, Wenzhou Medical University, Wenzhou 325035, China
JOURNAL OF ORGANIC CHEMISTRY
Volume: 83 Issue: 18 Pages: 10948-10958
DOI: 10.1021/acs.joc.8b01597
Published:SEP 21 2018
Document Type:Article
Abstract
Nitroxides can absorb both ultraviolet (UV) and visible light, and their electron can be excited from the pi-bonding orbital to the antibonding pi* orbital or the n-bonding orbital to the antibonding pi* orbital, respectively. Despite the reported UV-induced hydrogen atom transfer (HAT) process, the potential of nitroxides for visible light-excited photosynthesis is underexplored. Here we demonstrate that nitroxide can convert indole to its radical through a visible light-induced HAT process. A chiral phosphoric acid-catalyzed cyclization of the in situ-formed imine radical, followed by trapping by another molecule of nitroxide, provides the product in high yield and enantioselectivity. To highlight the novelty and efficiency of this strategy, an asymmetric total synthesis of natural product (-)-verrupyrroloindoline was accomplished in 5 steps.
全文链接：https://pubs.acs.org/doi/10.1021/acs.joc.8b01597
