Decatungstate Photocatalyzed Benzylation of Alkenes with Alkylaromatics

The direct benzylation of electrophilic alkenes with alkylbenzenes has been achieved by decatungstate photocatalysis in a high ionic strength medium (5:1 acetonitrile/water mixed solvents, 0.5M lithium perchlorate). The reaction has been extended to ring-substituted (Cl, F, CN) toluenes and further alkylbenzenes. Intramolecular selectivity (p-cymene, 4-methylanisole) and deuteration effects support the atom transfer character of the process that, however, requires a sufficient stabilization of the intermediate polar exciplex to occur. The reactivity of the decatungstate anion is compared with that of aromatic ketones, the benchmark of photochemical hydrogen/electron transfer processes.