Computerchemische Untersuchungen zur Addition an ein N-alkinyliertes Sulfoximin und zur Synthese eines trifluormethylierten 3-Oxazolins

  • Investigations on the addition to a N-alkynylated sulfoximine and on the synthesis of a trifluoromethylated 3-oxazoline with computational chemistry methods

Meister, Daniela; Bolm, Carsten (Thesis advisor); Schoenebeck, Franziska (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

In this doctoral thesis two projects were investigated with the help of density functional theory. First, an addition to a N-alkinylated sulfoximine was studied. This work was carried out based on previous experimental observations of our working group. The addition takes place with an azomethine ylide, which is known to dimerize under aqueous conditions with the release of formaldehyde. Since the atoms of formaldehyde are present in the here observed final product, an addition of formaldehyde to the triple bond of the N-alkinylated sulfoximine was investigated in two ways. In the first variant formaldehyde was added without any other additives. In the second variant, formaldehyde was protonated at the oxygen atom. Moreover, in a further variant the formation and hydrolysis of a heterocycle due to the addition of the azomethine ylide to the triple bond was investigated. With the help of energy diagrams and population analyses the variants were analyzed carefully for the R-enantiomers of the sulfoximines. However, it is also possible that derivatives of the dimerized azomethine ylide participate in the reaction. As numerous further derivatives of the ylide are possible, this was not investigated in the present work. In a second project a mechanistic investigation on the synthesis of a trifluorinated 3-oxazoline was carried out. The synthesis was developed in a project of our research group. With the help of energy diagrams and population analyses the radical trifluoromethylation and ring formation were investigated in detail. Several variants were studied with a special focus on the participation of the Togni reagent in the mechanism. It seems most likely that a transition metal-catalyzed mechanism takes place. First it follows a radical pathway, but after a single electron transfer it becomes an ionic mechanism. Two further variants for a completely radical mechanism without participation of a transition metal were studied, but they do not seem as likely as a transition metal-catalyzed mechanism.

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