Influence of the Nature of Boron‐Doped Diamond Anodes on the Dehydrogenative Phenol‐Phenol Cross‐Coupling

Abstract

Boron‐doped diamond (BDD) represents a powerful and innovative electrode material. In particular, in combination with fluorinated solvents such as 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP), the system exhibits the largest known electrochemical window of approximately 5 V in protic media. Furthermore, the anodic treatment allows the direct formation of oxyl radicals, which are known to exhibit specific reactivity. The electrochemical dehydrogenative phenol‐phenol cross‐coupling is a versatile and useful transformation to non‐symmetric biphenols. This electro‐organic conversion can be divided into two regimes: initial oxidation at the anode and the electrolyte‐controlled follow‐up reaction. This work intends to provide an answer about the influence of BDD electrodes on oxidation reactions in electrosynthesis. Depending on the electro‐organic transformation, the support material of BDD, its boron content, and its fabrication method have a significant influence on the electrosynthetic efficiency.

Supporting-Electrolyte-Free and Scalable Flow Process for the Electrochemical Synthesis of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

“…The reaction conditions were chosen on the basis of previous publications . Boron-doped diamond (BDD) as the anode material has proven its outstanding performance in anodic C–C coupling in many cases. ,− Additionally, the use of HFIP as the solvent is mandatory in electro-organic coupling reactions, as it is considered essential for obtaining the desired reaction selectivity. ,− By hydrogen bonding, the oxygen functionality is blocked, avoiding the typical C–O bond formation and/or the generation of polycyclic molecular architectures. ,− …”

HFIP in Organic Synthesis

“…This robustness is attributed to the ability of HFIP to strongly solvate individual substrates, stabilize reactive intermediates, as well as stabilize resultant products, thus preventing overoxidation. A separate analysis founds that the nature and composition of the BDD electrodes play a crucial role in these reactions . A more complete picture was painted when both the solvent system and electrode choice were dually studied.…”

Electrode Materials in Modern Organic Electrochemistry

“…More specific features of BDD and its general use has been well reviewed elsewhere. [137,[205][206][207] Theelectrochemical CÀHamination of arenes via Zincke intermediates (8)was reported by Yoshida using acarbon felt anode and platinum plate cathode,F igure 16. [208] However, the scope was limited to electron rich rings containing methoxy groups.I na ne ffort to widen the scope toward arenes with less electron density,W aldvogel explored the use of different anode materials in the reaction.…”

“…However, herein, we describe several synthetic organic examples that have required the use of a more inert electrode, which BDD has fulfilled. More specific features of BDD and its general use has been well reviewed elsewhere …”