Oxidative Palladium‐Catalyzed Carbocyclization of Enallenes under Electrochemical Conditions

Abstract Palladium‐catalyzed oxidative carbocyclizations of unsaturated allenes constitute powerful synthetic methods for the construction of functional group‐rich cyclic scaffolds via the coupling of two C−H bonds. The key downside of these otherwise very valuable processes is the need to utilize a stoichiometric amount of benzoquinone as a terminal oxidant, which can be elegantly addressed by the means of electrosynthesis. Herein, we report the development of an electrochemical version of the archetypical oxidative carbocyclization, that is, of enallenes. The conditions for the reaction were optimized and the electrochemical variant was successfully carried out for a number of substrates, albeit, somewhat lower yields were obtained compared to the original process, promoted by a chemical oxidant. However, the application of electric stimulus allowed for carrying out the reaction employing only a catalytic 20 mol% loading of benzoquinone, under simple constant current conditions and in an undivided cell. The need to use THF as a reaction solvent was identified as a key obstacle in achieving optimum efficiency under the electrochemical conditions, providing bearing for further electrification of the palladium‐catalyzed oxidative carbocyclizations of allenes.