Peroxides Facilitate Direct Methylations

By using peroxides to deliver methyl groups, a team led by Chao-Jun Li of McGill University, in Montreal, has devised an alternative strategy for the palladium-catalyzed methylation of aryl C–H bonds (J. Am. Chem. Soc. 2008, 130, 2900). The direct activation and alkylation of CH bonds typically requires a transition-metal catalyst to mediate coupling of an unactivated carbon atom with an alkenyl or alkyl group supplied by an alkene or an alkylboronic acid. Li, Yuhua Zhang, and Jianqing Feng determined that peroxides can also supply the alkyl group, leading to selective methylation (shown) or dimethylation of phenylpyridines and other aryl compounds. The researchers believe palladium inserts between the oxygen atoms at the heart of the peroxide, causing the peroxide to shed ketone and then alcohol by-products as it contributes a methyl group to the aryl substrate. The team is currently expanding the peroxide strategy to include direct aryl-cycloalkane coupling reactions, Li says.