PREDOMINANT O-ALKYLATION IN THE ATTACK OF FREE BENZYL CATION ON 2,6-DIMETHYLANISOLE

Labeled benzyl cation from the decay of side-chain multitritiated toluene was allowed to react with 2,6-dimethylanisole in n-hexane, MeNO2, and Et2O at room temp. The nuclear-decay formed (nucleogenic) benzyl cation displayed high selectivity toward the n-type center of the nucleophiles present, leading to predominant formation of benzyl 2,6-dimethylphenyl ether in n-hexane and MeNO2, via the O-benzylated oxonium intermediate. In n-hexane, the oxonium intermediate underwent partial isomerization, yielding the corresponding ring-substituted products. A mechanism involving a tight sandwich π complex is proposed to account for the solvent effect on product distribution. The mechanistic features of the benzylation process, deduced from the decay expts., are discussed and compared with those of related gas-phase and conventional Friedel-Crafts data.