Synthesis of 2- and 3-Benzoylindoles by Friedel-Crafts Reaction of Indole-2,3-dicarboxylic Anhydrides with Anisoles

Reaction of 1-benzylindole-2,3-dicarboxylic anhydride with anisole in the presence of titanium(IV) chloride gave 2-(4-methoxybenzoyl)indole-3-carboxylic acid as the sole product. However, l-benzenesulfonylindole-2,3-dicarboxylic anhydride with anisole afforded 3-(4-methoxybenzoyl)indole-2-carboxylic acid. These carboxylic acids could be converted to the corresponding benzoylindoles.