A Mechanistic Perspective on Photocatalytic EnT-Enabled C3-N-Heteroarylation of Aryl Quinoxaline via C(sp2)–C(sp2) Coupling

An EnT-mediated C3-N-heteroarylation of 2-aryl quinoxalines via decarboxylative radical-radical cross-coupling (C(sp2)-C(sp2)) with oxime esters is presented. Upon photoactivation, the triplet energy of the photocatalyst is transferred to both reacting partners (oxime ester and 2-phenylquinoxaline). The excited oxime ester undergoes decarboxylative fragmentation to a C-centered N-heteroaryl radical and an N-centered imine radical. The former attacks the C3 site of the quinoxaline diradical, while the latter acts as a hydrogen atom abstractor (HAA). Computational studies revealed that C-C bond formation with the heteroaryl radical is energetically more favorable than C-N bond formation.