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Zusammenfassung:
The extension of 'proton sponges' 1 and 2 by further anellation to 1,16-diaza[6]helicene (3) was of interest to define scope and limitation of 'proton sponge' properties. 3 was prepared by photocyclisation of 2,7-bis(3-pyridylvinyl)naphthalene 4 and by Pd-catalyzed aryl-aryl coupling of the corresponding tetrabromo derivative 7. As consequence of the helical structure, 3 does not show 'proton sponge' basicity. X-ray structure analyses of 3 and 3·2HBr are in accordance with these findings.
