In the reaction of pyrroles with tetrahalo‐1,4‐benzoquinones two different processes occur: the oxidation of pyrrole and the coupling reaction to 3,5,6‐trihalo‐2‐(pyrrol‐2‐yl)‐1,4‐benzoquinones. Excess of pyrrole results in doped polypyrrole as the principal reaction product. Excess of tetrahalobenzoquinone and dilution, provides the title compounds. The UV/Vis spectra and the electrochemical behaviour show that the title compounds have the HOMO localized at the pyrrole and the LUMO at the quinone ring.

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The electrochemical and chemical oxidative α,α'‐coupling of 3‐methoxy‐4‐methyl‐2‐pyrrolecarboxylic acid (2) and its ethyl ester 4 is compared with that of the corresponding 4‐methoxy‐2‐pyrrolecarboxylates (1 and 3 respectively). The β‐alkoxy substituent exerts a strong directing influence on its vicinal α‐position, which in the case of compounds 2 and 4 determines the 2,5'‐coupling and allows the isolation of the corresponding 1H,2'H‐2,2'‐bipyrrole 6 in the case of 4. For 2 the polypyrrole can be obtained by exhaustive electrochemical or chemical coupling, whereas in the case of 1 only the corresponding tetramers are formed. The structures of these tetrapyrroles, already described in the literature, here obtained by oxidation of 4‐alkoxy‐2‐pyrrolecarboxylic acid (1), have been reexamined: they are mixtures of tetramers with zwitterionic structure, have at least two substitution patterns and are partially oxidized to the corresponding bipyrrolylidenes.