Electrochemical C-N Coupling Reaction Mediated by π-Extended Haloarene Catalyst

Abstract

Hypervalent iodine is a useful reagent in synthetic organic chemistry,[1] but because these reagents are synthesized by reaction with stoichiometric amounts of oxidants, their large-scale use is associated with safety and environmental impact concerns. Hypervalent iodine can also be synthesized by electrochemical oxidation of the corresponding iodoarenes, and the electrochemically generated hypervalent iodine can be immediately reacted and used catalytically, i.e., as an electrochemical mediator, to enable a reaction system that is safe and generates little waste.[2] The use of hypervalent iodine as an electrochemical mediator has been reported previously, [3,4] but the number is still limited. In addition, no quantitative kinetic analysis of catalytic reactions has ever been performed. The presenters hypothesized that the following two issues are responsible for this situation: (i) the high oxidation potential of iodoarenes makes their selective oxidation difficult, and (ii) the instability of the radical cation.In this study, we designed and synthesized a novel π-extended iodoarene 1, and developed it as an efficient electrochemical mediator (Figure 1). The extended π system realized stabilization of the radical cation intermediate, as well as lowering the oxidation potential. Electrochemical oxidations of various N-Boc-2-aminobiphenyl analogues (2) were performed, and successfully gave cyclized product 3 in high yield in the presence of a base. Kinetic analysis of the electrocatalytic process based on Foot-of-the-Wave analysis (FOWA)[5] was also investigated.[6] In addition, we have also investigated the electrocatalytic reaction and kintetics using mediators with bromo- and chloro-anthracene structures to uncover the structure-reactivity relationship of haloarene mediators.[1] A. Yoshimura, V. V. Zhdankin, Chem. Rev., 2016, 116, 3328–3435. [2] M. Elsherbini, T. Wirth, Chem. Eur. J. 2018, 24, 13399–13407. [3] T. Fuchigami, T. Fujita, J. Org. Chem. 1994 , 59, 7190-7192. [4] A. Maity, B. L. Frey, N. D. Hoskinson, D. C. Powers, J. Am. Chem. Soc. 2020, 142, 4990−4995. [5] C. Costentin, S. Drouet, M. Robert, J.-M. Savéant, J. Am. Chem. Soc. 2012, 134, 11235–11242. [6] S. Yoshinaga, M. Atobe, N. Shida, ChemRxiv, 2022, DOI: 10.26434/chemrxiv-2022-sggqd.