Electrochemical Generation of N-Centered Radicals and Their Reactivity Toward Cyclization and Subsequent C─C Bond Cleavage

Abstract

N-containing heterocycles are widely used in medicinal chemistry, and they can be synthesized efficiently by the intramolecular cyclization of N-centered radicals. Furthermore, N-centered radicals also act as excellent hydrogen atom transfer (HAT) reagents. On the other hand, nitrogen atoms in the nitrogen-containing heterocycles are used as a handle to cleave stable five and six-membered rings. However, the electrochemical generation of N-centered radicals and their application in forming heterocycles have been extensively studied. Study beyond cyclization remains largely unexplored; in this manuscript, we summarize our new findings as follows. Under electrochemical conditions, the N─H bond is cleaved, forming an N-centered radical that adds to the double bond in a 6-endo-trig cyclization fashion. The newly formed C-centered radical reacts with oxygen and undergoes C─C bond cleavage to form the corresponding carbonyl compounds. The reactivity is dependent on the substituents present on nitrogen. In the case of aromatic amine-derived amide, the TEMPO trapping cyclization product was isolated. A mechanism has been proposed to explain the formation of the products.