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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Syntéza a využití N-heterocyklických karbenových ligandů na bázi helicenů / Synthesis and application of helicene-based N-heterocyclic carbene ligands

Gay Sánchez, Isabel January 2021 (has links)
The aim of my PhD Thesis was to explore the potential of helically chiral N-heterocyclic carbene (NHC) ligands in asymmetric catalysis. Helicenes and helicene-like molecules are inherently chiral. Their application in this field has been rather limited. To date, only a few examples of enantiopure helically chiral NHCs have been described in the literature. Using a well-established method based on the diastereoselective metal catalysed [2+2+2] cycloisomerisation of centrally chiral triynes as the key step, I have synthesised a series of optically pure 2H-pyran based penta- and hexahelicenes bearing an amino group on the terminal benzene ring. The triynes were prepared by a sequence of Sonogashira and Mitsunobu coupling reactions using the commercially available (S)-but-3-yn-2-ol as the source of chirality. The resulting aminooxa[5]- and aminooxa[6]helicenes were then converted into the corresponding 1,3-disubstituted imidazolium salts, from which, upon deprotonation, the helically chiral N- heterocyclic carbenes were generated. To evaluate the performance of the new helically chiral ligands, the enantioselective Ni0 - catalysed [2+2+2] intramolecular cycloisomerisation of prochiral triynes to nonracemic dibenzohelicenes was chosen as a model reaction. All the synthesised imidazolium salts provided,...

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