Anodic and Cathodic CC‐Bond Formation

Electrolysis allows the reactivity of a substrate to be changed, or its polarity to be reversed (“redox umpolung”). The carbon skeleton and the functional groups of a synthetic building block can thus be utilized more economically, and at the same time the number of reaction steps in multistage syntheses can be reduced. The tools necessary for an electrolytic process are a cell, a power source, electrodes, and an electrolyte, the latter being chosen in accordance with the reduction or oxidation potential of the substrate. A series of electroanalytical methods provides information on the electrode reaction mechanisms. At the anode, arenes, phenolic ethers, and electron-rich olefins dimerize via intermediate radical cations. In the Kolbe electrolysis, carboxylic acid anions decarboxylate to form radicals which can couple to form e.g. long chain alkene derivatives having pheromone activity, or add to ole-fins. At the cathode, activated olefins hydrodimerize via radical anions or, in the presence of appropriate reagents, can be acylated, alkylated, and carboxylated. Pinacols, crossed hydrodimers, and cyclic and arylated compounds are accessible via the cathodically produced radicals, while the formation of strained small rings or the reductive addition of halides to carbonyl compounds takes place through intermediate carbanions.