In vinyl nucleophilic substitution (S(N)vin) with the hydrochlorides or 4-toluenesulfonates of primary arylamines 1-alkyl-3-alkylaminopyrrole-2,5-diones form the corresponding 1-alkyl-3-arylaminopyrrole- 2,5-diones, which are also produced in situ from the corresponding arylaminofumarates and primary alkylamines.