Preparation of 2-oxindole derivatives

[PROBLEMS] To obtain a high-yield and high-quality compound by a simple operation without using a special raw material in the production of 2-oxindole derivatives which are important intermediates of various pharmaceuticals and dyes. Provision of new manufacturing methods that can be performed. [MEANS FOR SOLVING PROBLEMS] A corresponding hydrazone form of isatin is deoxygenated by a Wolff-Kischnar reduction reaction to obtain a 2-oxindole derivative, and then the reaction solution is crystallized while maintaining alkalinity. Process for obtaining a highly pure 2-oxindole derivative. [Selection figure] None