Preparation of 3,3-Diaryloxindoles by Superacid-Induced Condensations of Isatins and Aromatics with a Combinatorial Approach

3,3-Diaryloxidoles are prepared in high yields (62–99%) by reaction of isatin or substituted isatins with aromatics in triflic acid. The reaction shows a significant dependence on acid strength which suggests the formation of diprotonated, superelectrophilic intermediates . Reaction of isatin, benzene, and acid systems of varying strength (composed of CF₃SO₃H and CF₃CO₂H) showed that the acid strength must be more acidic than H₀ = -11.5 for complete conversion to product. Reaction of isatins with mixtures of aromatics allows for the preparation of libraries of 3,3-diaryloxindole products by combinatorial synthesis.