Behaviour of Radical Anions of Methoxy-Substituted Aromatics

As a continuation of our work on the reductive cleavage of anisole (1) and of dimethoxy- and trimethoxybenzenes (2) under electron-transfer conditions, we have investigated the regioselectivity of cleavage of the carbon-oxygen bonds of phenyl substituted anisoles. The result of the reduction with K metal in THF showed a marked difference in reactivity between the three isomers. Ortho- and para-phenylanisole reacted readily and gave mainly biphenyl (demethoxylation), whereas meta-phenylanisole was less reactive and gave mainly 3-hydroxybiphenyl (demethylation). These findings are at variance with those obtained under the same conditions for the three isomeric dimethoxybenzenes, where demethoxylation was the main reaction of the ortho- and meta-isomers, whereas the para-isomer showed very low reactivity and gave only demethylation. In both systems the results parallel the behaviour of the corresponding radical anions, as evidenced by E.S.R. spectroscopy.