In the presence of sodium methoxide in catalytic amounts, conjugated azoalkenes easily react with α-unsubstituted-or α-sub-stituted-β-dicarboxylate derivatives to give at first hydrazonic derivatives, by 1,4-conjugate addition, and, by increasing sodium methoxide up to stoichiometric amounts, new polyfunctionalized 1-amino-1H-pyrrol-2(3H)-ones.