Compound of formula where R 1 and R 3 are each a heteroaryl radical having five ring atoms, R 2 and R 4 are each independently selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12) -cycloalkyl, -(C 3 -C 12) -heterocycloalkyl, -(C 6 -C 20)-aryl; R 1 and R 3 may each independently be substituted by one or more substituents selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -O-(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -O-(C 3 -C 12)-cycloalkyl, -S-(C 1 -C 12)-alkyl, -S-(C 3 -C 12)-cycloalkyl, -COO-(C 1 -C 12)-alkyl, -COO-(C 3 -C 12)-cycloalkyl, -CONH-(C 1 -C 12)-alkyl, -CONH-(C 3 -C 12)-cycloalkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 3 -C 12)-cycloalkyl, -N-[(C 1 -C 12)-alkyl] 2, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl, -(C 3 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl-O-(C 1 -C 12)-alkyl, -COOH, -OH, -SO 3 H, -NH 2, halogen; and R 2 and R 4, if they are -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl or -(C 6 -C 20)-aryl, may each independently be substituted by one or more substituents selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -O-(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -O-(C 3 -C 12)-cycloalkyl, -S-(C 1 -C 12)-alkyl, -S-(C 3 -C 12)-cycloalkyl, -COO-(C 1 -C 12)-alkyl, -COO-(C 3 -C 12)-cycloalkyl, -CONH-(C 1 -C 12)-alkyl, -CONH-(C 3 -C 12)-cycloalkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 3 -C 12)-cycloalkyl, -N-[(C 1 -C 12)-alkyl] 2, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl, -(C 3 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl-O-(C 1 -C 12)-alkyl, -COOH, -OH, -SO 3 H, -NH 2, halogen; excluding the compounds of the formulae and R 1 and R 3 are each a heteroaryl radical having five ring atoms, R 2 and R 4 are each independently selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12) -cycloalkyl, -(C 3 -C 12) -heterocycloalkyl, -(C 6 -C 20)-aryl; R 1 and R 3 may each independently be substituted by one or more substituents selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -O-(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -O-(C 3 -C 12)-cycloalkyl, -S-(C 1 -C 12)-alkyl, -S-(C 3 -C 12)-cycloalkyl, -COO-(C 1 -C 12)-alkyl, -COO-(C 3 -C 12)-cycloalkyl, -CONH-(C 1 -C 12)-alkyl, -CONH-(C 3 -C 12)-cycloalkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 3 -C 12)-cycloalkyl, -N-[(C 1 -C 12)-alkyl] 2, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl, -(C 3 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl-O-(C 1 -C 12)-alkyl, -COOH, -OH, -SO 3 H, -NH 2, halogen; and R 2 and R 4, if they are -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl or -(C 6 -C 20)-aryl, may each independently be substituted by one or more substituents selected from -(C 1 -C 12)-alkyl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -O-(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -O-(C 3 -C 12)-cycloalkyl, -S-(C 1 -C 12)-alkyl, -S-(C 3 -C 12)-cycloalkyl, -COO-(C 1 -C 12)-alkyl, -COO-(C 3 -C 12)-cycloalkyl, -CONH-(C 1 -C 12)-alkyl, -CONH-(C 3 -C 12)-cycloalkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 3 -C 12)-cycloalkyl, -N-[(C 1 -C 12)-alkyl] 2, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl, -(C 3 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 3 -C 20)-heteroaryl-O-(C 1 -C 12)-alkyl, -COOH, -OH, -SO 3 H, -NH 2, halogen; excluding the compounds of the formulae and