Electrophilic Aromatic Alkylation by Hydroperoxides. Competition between Ionic and Radical Mechanisms with Phenols

Tertiary hydroperoxides have been utilized for the electrophilic alkylation of activated aromatic substrates, particularly phenols and phenol ethers. Cumyl (1) and tert-butyl (2) hydroperoxides have shown a greatly different behavior as concerns the catalysis and the regioselectivity. The best catalyst for 1 is TiCl(4), which is completely inactive with 2. With the latter an effective catalyst is FeCl(3), which, however, can give rise to a combination of electrophilic and radical reactions with alkyl phenols. 2,2'-Dihydroxy-3,3'-di-tert-butyl-5,5'-dimethyldiphenyl is obtained in high yields from p-cresol.