Green, Mild, and Efficient Friedel-Crafts Benzylation of Scarcely Reactive Arenes and Heteroarenes Under On-Water Conditions.

A metal-free Friedel-Crafts benzylation (FCB) of scarcely reactive arenes and heteroarenes has been performed under on-water conditions through an environmentally-sustainable procedure. Our catalytic strategy exploits the hydrophobicity of the resorcinarene macrocycle (1a). The proposed mechanism is based on the activation of benzyl chloride by H-bonding interactions with catalyst 1a. In fact, under on-water conditions the hydrophobic amplification of the strength of the H-bond interactions between the OH groups of the resorcinarene catalyst and the chlorine atom of the benzyl chloride, led to the polarization of the C-Cl bond that consequently promotes the electrophilic attack of the π-nucleophile. Thus, many arenes and heteroarenes have been efficiently benzylated under mild on-water conditions using resorcinarene 1a as the catalyst. The FCB of benzene is industrially relevant for the synthesis of diphenylmethane, thus we here extended the on-water procedure to the gram-scale synthesis of diphenylmethane, starting from benzene and benzyl chloride in the presence of resorcinarene catalyst 1a.