A novel catalytical feature of the hexameric resorcinarene capsule (C) is here highlighted. The self-assembled cage C has been exploited to promote a mild Friedel-Crafts benzylation of several arenes and heteroarenes. In silico studies show the existence of a catalytically relevant H-bonding interaction between the bridged water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C-Cl bond. A supramolecular control of the capsule on the reaction outcome is evidenced. Inside the inner space of the capsule, N-methylpyrrole is preferentially benzylated in the unusual -position, while mesitylene reacts faster than 1,3-dimethoxybenzene, despite the greater -nucleophilicity of this latter.