Wege zur Synthese ungewöhnlich substituierter Polyaromaten

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MachuyMareike_2012_10_01.pdf (5.31 MB)

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2012

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DOI:
http://dx.doi.org/10.22029/jlupub-10229

Abstract

This work established the basis for the selective synthesis of a family of pyrene derivatives with uncommon substitution patterns that are accessible via electrophilically induced cyclization reactions. The construction of these molecules with desirable optoelectronic properties was started by coupling of two phenyl-moieties via Suzuki-Miyaura cross-coupling to give sterically demanding 2,6-dibromobiphenyls. Through this step, we gained access to a group of these biphenyls. After characterization, we optimized some of the parameters of this synthetic step. Using arylethynyls in Kumada-Tamao-Corriu cross-coupling gave 2,6-phenylethynylbiphenyls that act as pyrene cyclization precursors. Subsequent cyclization lead to 4,10-aryl substituted pyrene derivatives, which display blue shifts in UV/Vis spectra and mirros these in fluorescence spectra.Beside these synthetic steps, we successfully tested a diamantyl-salt (di-4-diamantyl-n-butylphosphonium iodide) prepared in our group in Suzuki-Miyaura and Sonogashira-Haghiara cross-coupling reactions, respectively. We also synthesized bis(arylethynyl)benzenes (enediynes) as precursors for thermally induced 1,6- and 1,5-cyclizations, and performed several test reactions in order to determine the influence of the substituents of the aryl moieties of these enediynes on the progress of these annulations and their ring size. In these first experiments, we found that these cyclization proceed in the 1,5-Schreiner-pathway, if the substrate carries radical-stabilizing substituents and that this reaction-pathway is not caused by steric effects as postulated by Pascal et al. Other experiments include an electrophilically induced casacade cyclization of such enediyne- and related enhanced systems and mechanistic studies that have been supplemented by computations. Several computations were carried out to compare Arduengo-type carbenes as ligands with their NHC-diamantyl-analogue for potential use of NHCs as palladium-catalysts. The computations reveal that the proton affinity of these adamantyl and diamantyl derived systems are in the same range as computed for the mesityl substituted anlogues.

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