NEW MATERIAL:1-Acyl-2,3-diacyloxyindolines of formula I (Acyl is 1W4C acyl; R1, R2, R3, R4 are H, halogen, hydroxyl, 1W3C hydrocarbyl, 1W3C alkoxy; R6 is 1W3C hydrocarbyl) or 1-acyl-2-hydroxy-3-acyloxyindoline of formula II.

EXAMPLE: 1-Acetyl-2-hydroxy-3-acetoxyindoline.

USE: Starting material of indoxyl which is a synthetic intermediate for indigo dyes.

PREPARATION: The electrolytic oxidation of 1-acylindoline such as 1-acetyl-indoline or 1-acylindole such as 1-acetylindole under mild temperature conditions is conducted in a solvent of lower aliphatic carboxylic acids in the presence of a base, preferably an amine under supplying the necessary amount of electricity with an appropriate density to produce the objective compound.