Efficient synthesis of halo indanones via chlorosulfonic acid mediated Friedel–Crafts cyclization of aryl propionic acids and their use in alkylation reactions

Several halo indanones were synthesized from benzyl Meldrumʹs acid derivatives in two steps. Although several Lewis acids are effective for the Friedel–Crafts ring-closing reaction on more electron-rich arenes, in the case of the electron-deficient arenes this chemistry is not efficient. Here it is reported that chlorosulfonic acid (used as solvent) is an efficient reagent for cyclization of electron-withdrawing arenes. These molecules are potentially useful for subsequent alkylation reactions. The selective alkylation of 5,7-dibromo indanone is demonstrated using Pd-catalyzed Grignard coupling to provide monoalkylated indanone in good yield.