The cyclodehydration of bis(pyridiniummethyl)methylbenzenes 3a-b in polyphosphoric acid leads to methyl-substituted diazoniapentaphene salts 4a-b instead of linear diazoniapentacene derivatives, while the 1,3-bis(pyridiniummethyl)bromobenzene 3d forms a semi-betaine 4a,12a-diazoniapentaphen-14-olate 4d under these conditions. The mechanistic details of this rearrangement-cyclodehydration sequence may be explained by an intramolecular ipso-addition to the substituted benzene moiety, followed by an [1,2]-methyl shift in case of 4a-b or HBr elimination in case of 4d. The proposed mechanism was confirmed by the isolation of the intermediate hydroxy derivative 10b from the cyc-
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