Photoinduced Transition-Metal-Free Chan-Evans-Lam-Type Coupling: Dual Photoexcitation Mode with Halide Anion Effect.

Herein, we report a photoinduced transition-metal-free C(aryl)-N bond formation between 2,4,6-tri(aryl)boroxines or arylboronic acids as an aryl source and 1,4,2-dioxazol-5-ones (dioxazolones) as an amide coupling partner. Chloride anion, either generated by photodissociation of chlorinated solvent molecules or added separately as an additive, was found to play a critical cooperative role, thereby giving convenient access to a wide range of synthetically versatile -arylamides under mild photo conditions. The synthetic virtue of this transition-metal-free Chan-Evans-Lam-type coupling was demonstrated by large-scale reactions, synthesis of N-labeled arylamides, and applicability toward biologically relevant compounds. On the basis of mechanistic investigations, two distinctive photoexcitations are proposed to function in the current process, in which the first excitation involving chloro-boron adduct facilitates the transition-metal-free activation of dioxazolones by single electron transfer (SET), and the second one enables the otherwise-inoperative 1,2-aryl migration of the thus-formed -chloroamido-borate adduct.