Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

The oxidative cross‐coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2′‐biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent‐free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale‐up and inherently safe. The implementation of O‐silyl‐protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2,2′‐biphenols. The use of a bulky silyl group to block one hydroxyl moiety makes the final product less prone to oxidation. Furthermore, the partially silyl‐protected 2,2′‐biphenols are versatile building blocks that usually require tedious or low‐yielding synthetic pathways. Additionally, this strategy facilitates a large variety of new substrate combinations for oxidative cross‐coupling reactions.