The amidine is prepared by condensing a thiophene compound of formula ##STR8## with an ortho-halonitrobenzene, in the presence of a base, for example sodium hydride, in a solvent such as tetrahydrofuran or n-butyl lithium in tetrahydrofuran, or potassium carbonate or lithium hydroxide in dimethylsulphoxide or aqueous sodium hydroxide in dimethylsulfoxide, or with a tetraalkyl-ammonium salt in a tw