Preparation of pyrrolo[3,4-c]pyrroles

A process for the preparation of a 1,4-diketopyrrolo[3,4-c]pyrrole of formula I ##STR58## wherein each of R.sub.1 and R.sub.2 independently of the other is phenyl or said phenyl substituted by one or two fluorine, chlorine or bromine atoms or mixtures thereof, by one, two or three methoxy or methyl groups or mixtures thereof with chlorine atoms, by cyano, by dimethylamino, by trifluoromethyl, by alkoxycarbonyl of 2 to 3 carbon atoms, by tert-butyl, by cyanophenyl, by acetyl or by alkylbenzoyloxy of 11-14 carbon atoms;

• biphenylyl;
• naphthyl or said naphthyl substituted by methoxy anthryl;
• phenanthryl;
• pyridyl or said pyridyl substituted by methyl or by amyloxy;
• quinolyl;
• furyl or thienyl, which consists essentially of
• condensing an unsymmetrical or symmetrical dialkyl or diaryl succinate, or monoalkyl monoaryl succinate or dicyclohexyl succinate with two moles of nitrile per each mole of succinate, wherein the nitrile is of formula II or of formula III
• R.sub.1 CN (II)
• or
• R.sub.2 CN (III)
• or is an equimolar mixture of nitriles of formulas II and III;
• in an organic solvent which is an alkanol, a glycol, an ether, a glycol ether, a dipolar aprotic solvent, an aliphatic hydrocarbon, an aromatic hydrocarbon, benzene substituted by alkoxy or by halogen, pyridine, picoline or quinoline, or a mixture thereof;
• in the presence of 0.1 to 10 moles of a strong base per each mole of succinate, wherein said base is an alkali metal, an alkali metal amide, an alkali metal hydride, an alkali metal alcoholate or an alkaline earth metal alcoholate;
• at a temperature of 60.degree. to 140.degree. C., and
• hydrolyzing the condensation reaction product obtained in water, a lower alkanol, a mineral acid or an organic acid or mixture thereof to form the compound of formula I.