Selective catalytic carbanionic ethylation of methylphenols: influence of catalyst and substitution pattern

Addition of ethylene to the carbanions formed by the metallation of the lithium salts of di- and trimethylphenols by the strongly basic system, n-BuLi-LiK(OCH₂CH₂NMe₂)₂ provides a useful synthetic route to a range of alkylphenols. The ease of alkylation of the methyl groups decreases in the order ortho>meta>para while the inclusion of Mg(OCH₂CH₂OEt)₂ in the catalyst restricts alkylation to the methyl groups ortho to the hydroxy group. Dialkylation occurs only at the ortho-methyl groups and only if the adjacent meta-position is unsubstituted. The potential of these products for the synthesis of sterically hindered ligands is outlined.