Electrochemical Oxidation of Aryl Boronic Acids via Fluoride Activation and Alternating Polarity Electrolysis for Aryl C–P Bond Formation

Aryl organoboron reagents play an important role in modern organic synthesis, and interest in radical‐based coupling reactions from these precursors has grown rapidly. However, direct electrochemical generation of aryl radicals from aryl boronic acids, ArB(OH) 2 , remains understudied due to their high oxidation potentials ( E ox > 2 V vs. Fc/Fc + ) and challenges associated with electrochemical processes such as electrode passivation. Aryl potassium trifluoroborate salts (ArBF 3 K) can be oxidized efficiently to aryl radicals is previously reported using alternating polarity electrolysis. Building on this, it is combined alternating polarity electrosynthesis with in situ fluoride activation to generate redox‐active aryl fluoroborate intermediates, ArBF(OH) 2 and/or ArBF 2 (OH), which have significantly lower oxidation potentials than their parent boronic acids or trifluoroborates. Moreover, it is found that for highly electron deficient aryl boronic acids with oxidation potentials higher than 1.7 V versus Fc/Fc + , a different mechanism is proposed where aryl boronic acids underwent ipso ‐substitution with oxidatively generated P(OEt) 3 radical cation. Overall, this dual mechanistic pathway allows an efficient radical‐based functionalization of a broad range of aryl boronic acids to form aryl CP bonds.