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•3?H2O

We report a highly efficient FriedelCrafts 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(ClO4)2 center dot 3H2O was identified as a powerful catalyst for this reaction, and is significantly more efficient than other screened metal perchlorate hydrates and Bronsted acids such as HOTf and HClO4. The high catalytic property of Hg(ClO4)2 center dot 3H2O 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.