Sulfonamides as N-Centered Radical Precursors for C–N Coupling Reactions To Generate Amidines
Guogang Deng, Zhuo Chen, Yifeng Bai, Lening Zhang, Dazhen Xia, Shengzu Duan, Wen Chen, Hongbin Zhang, Patrick J. Walsh, Xiaodong Yang
Abstract
Nitrogen-centered radicals (NCRs) are valuable intermediates for the construction of C–N bonds. Traditional methods for the generation of NCRs employ toxic radical initiators, transition metal catalysts, photocatalysts, or organometallic reagents. Herein, we report a novel strategy for the generation of NCRs toward the construction of C–N bonds under transition-metal-free conditions. Thus, super-electron-donor (SED) 2-azaallyl anions undergo single-electron transfer (SET) with sulfonamides, forming aminyl radicals (R 2 N •, R = alkyl) and culminating in the generation of amidines bearing various functional groups (33 examples, up to 96% yield). Broad substrate scope and gram-scale telescoped preparation demonstrate the practicality of this method. Radical clock and electron paramagnetic resonance (EPR) experiments support the proposed radical coupling pathway between the generated N-centered radical and the C-centered 2-azaallyl radical.