A. Granzhan, H. Ihmels, Katya Mikhlina
Oct 1, 2005
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0
Influential Citations
3
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Journal
European Journal of Organic Chemistry
Abstract
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 cyclization of 3a in refluxing HBr and conversion of 10b to the final product 4a by dehydration in polyphosphoric acid. Electronic absorption and fluorescence properties of the previously unknown diazoniapentaphene salts have been studied. Photophysical properties of 4a–b resemble the ones of the parent diazoniapentaphene salts, while semi-betaine 4d possesses a red-shifted absorption and fluorescence maxima, along with significant solvatochromism with respect to the absorption properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)