A highly efficient Friedel-Crafts reaction of 3-hydroxyoxindoles and aromatic compounds to 3,3-diaryl and 3-alkyl-3-aryloxindoles catalyzed by Hg(ClO4)2·3H2O.

We report a highly efficient Friedel-Crafts reaction of 3-alkyl or 3-aryl 3-hydroxyoxindoles with a variety of aromatic and heteroaromatic compounds to unsymmetrical 3,3-diaryloxindoles or 3-alkyl-3-aryloxindoles, which are interesting medicinal targets and useful building blocks for the synthesis of natural products. Hg(ClO(4))(2)·3H(2)O was identified as a powerful catalyst for this reaction, and is significantly more efficient than other screened metal perchlorate hydrates and Brønsted acids such as HOTf and HClO(4). The high catalytic property of Hg(ClO(4))(2)·3H(2)O originates from the unprecedented dual activation effects of aromatic mercuration, which could generate a strong protic acid to facilitate the generation of a carbocation at the C3-position of oxindoles and simultaneously form the more reactive nucleophilic reaction partner.