Sequential Vinyl Radical Cyclization/Fixation of Carbon Dioxide through Electrochemical Reduction of Vinyl Bromide in the Presence of an Electron‐Transfer Mediator

Constant current electrolysis of vinyl bromide in DMF containing 0.1 M Bu4NBF4 using an undivided cell equipped with a platinum plate cathode and a magnesium rod anode in the presence of an electron transfer mediator, methyl 4-tert-butylbenzoate, and carbon dioxide resulted in selective generation of a vinyl radical, for which cyclization followed by fixation of carbon dioxide with a carbon-carbon bond formation gave γ,-unsaturated carbo- and heterocycle carboxylic acids in moderate to good yields. A vinyl radical could be selectively generated under the electrolysis conditions, and the following reaction of anion species, generated by one-electron reduction of the resulting cyclized radical, with carbon dioxide took place efficiently. These results and cyclic voltammetry indicate that methyl 4-tert-butylbenzoate plays an important role in the generation of vinyl radicals from vinyl bromides. The resulting cyclized γ,-unsaturated carboxylic acid was successfully applied to stepwise and direct iodo-lactonization to give the corresponding bicycle γ-lactones in good yields.