Photoinduced Bartoli Indole Synthesis by the Oxidative Cleavage of Alkenes with Nitro(hetero)arenes
Hongyun Qin, Ruihua Liu, Zemin Wang, Feng Xu, Xiaowei Li, Cong Shi, Jiashu Chen, Wenlong Shan, Chao Liu, Pan Xing, Jiqiang Zhu, Xiangqian Li, Dayong Shi
Abstract
Given the unique charm of dipole chemistry, intercepting N-O=C dipoles precisely generated by designed processes to develop novel reactivity has become a seminal challenge. The polar fragmentation of 1,3,2-dioxazolidine species generated through the radical addition of excited nitro(hetero)arenes to alkenes represents a significantly underappreciated mechanism for generating N-O=C dipoles. Herein, we present a photoinduced Bartoli indole synthesis by the oxidative cleavage of alkenes with nitro(hetero)arenes. Various indoles and azaindoles are constructed through the multi-step spontaneous rearrangement of carbonyl imine intermediates generated by the polar fragmentation of 1,3,2-dioxazolidine species. Mechanism studies and DFT calculations support that the reaction involves radical cycloaddition, ozonolysis-type cycloreversion, intramolecular H-shift of carbonyl imines, and 3,3-sigmatropic shift of O-Alkenyl hydroxylamines, etc. The implementation of continuous- flow photochemistry, in particular, significantly enhances efficiency, thereby overcoming obstacles to the commercialization process.