Acid-Catalyzed Condensations of Ninhydrin with Aromatic Compounds. Preparation of 2,2-Diaryl-1,3-indanediones and 3-(Diarylmethylene)isobenzofuranones1.

Ninhydrin (1) reacts with aromatic compounds in acid solution to give condensation products. In H2SO4, 1 reacts with arenes to give 2,2-diaryl-1,3-indanediones (2a-f). In superacidic triflic acid (CF3SO3H, TfOH), 1 reacts with arenes to give 3-(diarylmethylene)isobenzofuranones (3a-e). Products 3a-e are proposed to have formed by a condensation and rearrangement involving dicationic intermediates. Benzo[f]ninhydrin also reacts with C6H6 in H2SO4 to give a similar condensation product.