Selective Formation of 4,4'-Biphenols by Anodic Dehydrogenative Cross- and Homo-Coupling Reaction.

A simple and selective electrochemical synthesis by dehydrogenative coupling of unprotected 2,6- or 2,5-substituted phenols to the desired 4,4'-biphenols is reported. Using electricity as the oxidizing reagent avoids pre-functionalization of the starting materials, since a selective activation of the substrates takes place. Without the necessity for metal-catalysts or the use of stoichiometric reagents it is an economic and environmentally friendly transformation.

Metal- and Reagent-Free Dehydrogenative Formal Benzyl-Aryl Cross-Coupling by Anodic Activation in 1,1,1,3,3,3-Hexafluoropropan-2-ol.

A selective dehydrogenative electrochemical functionalization of benzylic positions that employs 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) has been developed. The electrogenerated products are versatile intermediates for subsequent functionalizations as they act as masked benzylic cations that can be easily activated. Herein, we report a sustainable, scalable, and reagent- and metal-free dehydrogenative formal benzyl-aryl cross-coupling.

A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol.

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary.

Modern Electrochemical Aspects for the Synthesis of Value-Added Organic Products.

The use of electricity instead of stoichiometric amounts of oxidizers or reducing agents in synthesis is very appealing for economic and ecological reasons, and represents a major driving force for research efforts in this area. To use electron transfer at the electrode for a successful transformation in organic synthesis, the intermediate radical (cation/anion) has to be stabilized. Its combination with other approaches in organic chemistry or concepts of contemporary synthesis allows the establishment of powerful synthetic methods.

Electrifying Organic Synthesis.

The direct synthetic organic use of electricity is currently experiencing a renaissance. More synthetically oriented laboratories working in this area are exploiting both novel and more traditional concepts, paving the way to broader applications of this niche technology. As only electrons serve as reagents, the generation of reagent waste is efficiently avoided.

Unexpected high robustness of electrochemical cross-coupling for a broad range of current density.

Electro-organic synthesis is a powerful technique for the sustainable preparation of compounds. However, many electrosynthetic reactions require complex equipment, are limited to a very narrow current density range, or have very long reaction times; some also involve nonselective transformations and bad scalability. The robust and selective synthesis of nonsymmetric biphenols and partially protected derivatives is established by anodic C-C cross-coupling.

Single and Twofold Metal- and Reagent-Free Anodic C-C Cross-Coupling of Phenols with Thiophenes.

The first electrochemical dehydrogenative C-C cross-coupling of thiophenes with phenols has been realized. This sustainable and very simple to perform anodic coupling reaction enables access to two classes of compounds of significant interest. The scope for electrochemical C-H-activating cross-coupling reactions was expanded to sulfur heterocycles.

Synthesis of meta-Terphenyl-2,2''-diols by Anodic C-C Cross-Coupling Reactions.

The anodic C-C cross-coupling reaction is a versatile synthetic approach to symmetric and non-symmetric biphenols and arylated phenols. We herein present a metal-free electrosynthetic method that provides access to symmetric and non-symmetric meta-terphenyl-2,2''-diols in good yields and high selectivity. Symmetric derivatives can be obtained by direct electrolysis in an undivided cell.

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.

Source of Selectivity in Oxidative Cross-Coupling of Aryls by Solvent Effect of 1,1,1,3,3,3-Hexafluoropropan-2-ol.

Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions.