Selective catalytic carbanionic ethylation of methylphenols: influence of catalyst and substitution pattern
摘要:
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. (c) 2006 Elsevier Ltd. All rights reserved.