Fragile intermediate identification and reactivity elucidation in electrochemical oxidative α-C(sp)-H functionalization of tertiary amines

• Published in: Chemical science (Cambridge) Vol. 14; no. 15; pp. 4152 - 4157
• Main Authors: Liang, Kailun, Zhang, Dongmei, Su, Yanming, Lu, Lijun, Hu, Jun, Chen, Yi-Hung, Zhang, Xinxing, Lei, Aiwen, Yi, Hong
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 12.04.2023; Royal Society of Chemistry; The Royal Society of Chemistry
• Subjects: Amines; Amino radical; Cations; Chemistry; Chemistry, Multidisciplinary; Electrochemical oxidation; Electron transfer; Functional groups; Mass spectrometry; Oxidation; Oxidizing agents; Photoredox catalysis; Physical Sciences; Science & Technology; HYDROGEN EVOLUTION; ACTIVATION; MASS-SPECTROMETRY; BONDS
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d3sc00527e

The direct α-C(sp 3 )-H functionalization of widely available tertiary amines holds promise for the rapid construction of complex amine architectures. The activation of C(sp 3 )-H bonds through electron transfer and proton transfer by oxidants, photoredox catalysis and electrochemical oxidation have received wide attention recently. In these reactions, the direct capture and identification of the key reactive radical intermediates are technically difficult due to their short life-time. Herein, an online electrochemical mass spectrometry (MS) methodology was utilized to probe the short-lived intermediates in the electrochemical oxidative α-C(sp 3 )-H functionalization of tertiary amines. The resulting electrochemical oxidation intermediates, α-amino radical cation and iminium cation were successfully detected. Further, the α-amino C(sp 3 ) radical added to the double bond of a phenyl trans -styryl sulfone, yielding another C(sp 3 ) radical that leads to the final vinylation. Based on the mass spectrometric elucidation of the reactivity of the α-amino radical, a scale-up electrochemical radical vinylation methodology was established, with which a large variety of allylic amines with broad functional group tolerance were synthesized. An online electrochemical mass spectrometry (MS) methodology has been developed and utilized to probe the short-lived intermediates in electrochemical oxidative α-C(sp 3 )-H functionalization of tertiary amines.