Photochemie von alpha-Naphthylacrylaten: Synthese von (+)-Delavatin A, Acenaphthenen und Naphthocyclobutenen

Das primäre Ziel dieser Arbeit war die Synthese des Naturstoffs Delavatin A. Hierzu wurde eine photochemische Acenaphthensynthese unter Einsatz von sichtbarem Licht entwickelt. Nach anfänglicher Optimierung mit UV-Licht durch statistische Versuchsplanung gelang die Übertragung auf sichtbares Licht d...

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Bibliographic Details
Main Author: Peez, Theodor
Contributors: Koert, Ulrich (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2019
Online Access:PDF Full Text
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Table of Contents: The primary goal of this PhD thesis was the synthesis of the natural product delavatine A. To this end, a novel photocyclization employing visible light was developed. After initial optimization using UV-light and DOE, the application of visible light was enabled by energy transfer catalysis. By performing the cyclization on 20 substituted acrylates, the high functional group tolerance of the reaction was shown. CV and UV/VIS measurements, a Stern-Volmer quenching experiment and experiments with alternate triplet sensitizers confirmed the course of the reaction via a triplet state and excluded redox processes. By using DFT-calculations the primary amine was revealed to function as a H-atom shuttle, enabling a suprafacial H-Atom transfer. The synthesis of delavatine A was successfully accomplished by employing the developed photocyclization as the key step. The first enantioselective hydrogenation of an acenaphthylene to azaacenaphthene was also developed for the synthesis. During establishment of the scope an unusual reaction was observed: Substrates possessing a benzylic hydrogen in 2-position were found to furnish naphthocyclobutenes in high diastereomeric ratios. After optimization, a broad scope was shown by successful application to 17 derivatives, which also allowed for the diastereoselective synthesis of adjacent quaternary stereocenters. Isotope labeling showed an unusual C-C 1,5-HAT to be operational. CV and UV/VIS measurements as well as a Stern-Volmer quenching experiment show that the reaction proceeds via the triplet state and rules out any redox processes. The energetic path of the reaction was elucidated by employing DFT calculations. Additionally, a divergent Stereochemistry was found for different substrates. The reasons for this were discussed based on DFT calculations. Synthetic use of the obtained naphthocyclobutenes was shown by opening of the four membered ring either thermally or chemically, by which different products were obtained.