ARYL RADICALS FROM ELECTROCHEMICAL REDUCTION OF ARYL HALIDES - ADDITION ON OLEFINS

Aryl radicals generated by direct and indirect (by means of an aromatic anion radical mediator) electrochemistry are reacted with olefins in liquid ammonia and in organic solvents (Me2SO, MeCN, DMF). The arylated product is obtained in good yield in the latter case. In pure liquid NH3, the yields are extremely poor. They are improved upon addition of a proton donor such as urea or water; further increase of yields is obtained upon addition of 2-propanol. A reaction mechanism is proposed based on these observations and on the results of deuterium incorporation experiments. Cyclic voltammetry is used to determine the rate constant of the key step in the mechanism, viz, the addition of the aryl radical to the olefin, through its competition with its reaction with nucleophiles in the framework of an S(RN)1 substitution process.