The invention relates to a preparation method of 3-(2-methylindolyl-3-)pyrryl-2,5-dione, which comprises the following steps: (1) adding 2-methylindole,
maleimide and Lewis acid in a mol ratio of 1.0:(1.0-1.5):(0.2-1.0) into reaction
solvent, and reacting under
reflux at
room temperature to 100 DEG C for 5-24 hours, thereby obtaining a yellow white solution; and (2) evaporating to remove the
solvent, adding water, stirring, carrying out vacuum
filtration, and recrystallizing the obtained
solid with
ethanol to obtain the 3-(2-methylindolyl-3-)pyrryl-2,5-dione. In the process of preparing the 3-(2-methylindolyl-3-)pyrryl-2,5-dione, by using
boron trifluoride and other Lewis acid as a catalyst, the reaction time is shortened, and the treatment of three wastes is lowered. The method has the advantages of higher yield, accessible raw materials, low cost, simple reaction operation and short reaction
route, can easily implement industrial production, and has wide favorable application prospects.