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.

Methylphenols are converted in one pot to bulky, highly lipophilic homologues by the superbase catalysed addition of ethylene.