Succinic anhydride is treated with 1 equiv of aniline, then the product is heated strongly (dehydration). The final organic product is

Aniline opens the cyclic anhydride (carboxylate leaving group) to give the amide-acid 4-anilino-4-oxobutanoic acid. On strong heating the amide N attacks the CO2H group intramolecularly with loss of $\mathrm{H}{}_2\mathrm{O}$, closing a five-membered imide: 1-phenylpyrrolidine-2,5-dione.