Direct Observation of Enamine-Derived Radicals with Time-Resolved Electron Paramagnetic Resonance

17 January 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


This study presents the direct observation of α-imino radical intermediates involved in the photoredox catalytic activation of enamines using the ultrawide single sideband phase-sensitive detection time-resolved electron paramagnetic reso-nance (U-PSD TREPR) technique. Enamines have been exten-sively used in singly occupied molecular orbital (SOMO) catal-ysis. The redox properties of enamines allow for facile oxida-tion, forming α-imino radical species that participate in vari-ous coupling reactions. Despite the synthetic value of these transformations, direct observation of the key radical inter-mediates has been limited. The U-PSD TREPR technique ena-bled direct in-situ observation of transient enamine radical cation and α-imino radical intermediates for the first time. Spectroscopic characterization and kinetic analysis provided insights into the structure and reactivity of these intermedi-ates. The results demonstrated the involvement of enamine radical cations as the key intermediates in the photoredox transformations by primary aminocatalysis.


Radical Chemistry
Direct Observation
Reaction Intermediates

Supplementary materials

Supporting information
Details for experimental procedures, spectra simulation, kinetic fitting and compound characterization


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