Preparation of 2-Heteroaryl-indolin-3-ones by Acid-Mediated Intramolecular Cyclization in Batch and Flow

An intramolecular cyclization strategy to synthesize nitrogen-rich and biologically important 2-heteroaryl-indolin-3-ones has been developed in both batch and flow. Using high-throughput screening, citric acid in a dimethylformamide/water mixture was found to facilitate the reaction under batch conditions, which can tolerate substituted phenyl rings, quinolines, and naphthalenes with a variety of electronic and steric properties. The reaction was reoptimized for flow conditions using design of experiments, complementing the batch conditions for some substrates with greatly reduced reaction times.