Synthese und Metallierung von Fulvenen

  • Synthesis and metalation of fulvenes

Sieverding, Paul; Kögerler, Paul (Thesis advisor); Bolm, Carsten (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

The present dissertation tackles four distinct but related topics primarily concerning the chemistry of pentafulvenes (for shake of brevity hereinafter pentafulvenes will be referred to as fulvenes). The first topic is the pyrrolidine-buffer catalyzed synthesis of fulvenes from carbonyls and cyclopentadiene in acetonitrile as the solvent. This new and improved method for the synthesis of fulvenes was not only carried out synthetically but was also studied with respect to its selectivity and reaction kinetics. Additionally, models providing fundamental insight to the kinetics of fulvene formation were derived. The second topic covers the synthesis of chiral fulvenes. The first enantioselective organocatalytic synthesis of a fulvene from a racemic α,α-disubstituted aldehyde (2-phenylpropanal) is presented. For this purpose, chiral organocatalysts, as for example L-proline, were used instead of the achiral pyrrolidine. In particular, the use of combinations of hydrogen-bond donors and L-proline, in situ forming supramolecular, modularly designed organocatalysts, leads to improvements of the yield and selectivity of fulvene formation. In addition to a large number of syntheses, a systematic NMR-kinetic study was conducted providing a deeper insight into the processes leading to the enantioselectivity observed during the formation of 6-(1-phenylethyl)fulvene. Moreover, theoretical calculations were performed to corroborate the conclusions from experimental results. The overall results contribute to a better mechanistic understanding of the KNOEVENAGEL reaction, that is closely related to the fulvene formation, and furthermore provide a new method for the synthesis of enantioenriched substituted cyclopentadienes. Results on the reactions of the aforementioned 6-(1-phenylethyl)fulvene with hydride donors or carbon nucleophiles are the base of the third topic. In addition to providing an example for the general synthetic utility of α-chiral fulvenes, those results show the addition-reaction of carbon nucleophiles to these fulvenes to proceed diastereoselectively, although the observed diastereoselectivities were low. The latter results represent a first approach to constitute rules for the prediction of the diastereoselectivity of the addition of carbon nucleophiles to fulvenes. The fourth topic addresses the synthesis and conversion of trifunctional cyclopentadienides that were partially prepared from fulvenes. Here, the focus of the experiments was the synthesis of lanthanoid complexes of those trifunctional cyclopentadienyl ligands. In the present thesis and during the course of the work, the successful new and improved methods for the synthesis and conversion of fulvenes are the center of attention.

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