Preparation of 3,3-diaryloxindoles by superacid-induced condensations of isatins and aromatics with a combinatorial approach

Yields ranging from 62 to 99% were obtained for 3,3-diaryloxindoles by reacting isatins or substituted isatins with aromatics in the presence of triflic acid. The reaction was found to be dependent on the concentration of the acid, thereby indicating the formation of diprotonated, superelectrophilic intermediates. Moreover, the reaction of acid systems, benzene and isatin of different strength revealed that the acid strength must exceed Ho = -11.5 for completion of the conversion to the end product.