2,4,2',4'-tetramethyl-5,5'-(2-ethoxycarbonyl-ethane-1,1-diyl)-bis-pyrrole-3-carboxylic acid diethyl ester

(4-ethoxycarbonyl-3,5-dimethyl-pyrrol-2-ylmethylene)-malonic acid diethyl ester

4-ethoxy-2,4-dioxobutanoate

3,3-bis-(4-ethoxycarbonyl-3,5-dimethyl-pyrrol-2-yl)-propionic acid