Ein Beitrag zur Aufklärung des Mechanismus der Konfigurationsumkehr von α-Schwefel- [Alpha-Schwefel-], Selen- und Tellur-substituierten Alkyl- und Benzyllithium-Verbindungen

Chiral organolithium compounds possess a high synthetic potential for their utilization as synthons in stereoselective synthesis, provided however, that these species are configurationally stable. The objective of this dissertation is the determination of the configurative stability of chiral, alfa-heteroatom substituted organolithium spezies as well as the clarification of the underlying racemication mechanism. The configurative stability of alfa-bromine, alfa-selenium und alfa-tellurium substituted alkyllithium compounds was determined by two independent methodologies. The first part of the dissertation deals with investigations based on the Hoffmann Test, in which the organolithium species is trapped at low temperature with a suitable electrophilic trapping reagent. The outcome of this test revealed that the rate of the racemisation is slower than the rate of the reaction between the organolithium species and the electrophile. In the second part of the dissertation dynamic 1H-NMR spectroscopy is applied for the quantitative determination of racemisation barriers. The gained structure-stability relationships for a series of chiral organolithium species revealed details of the racemization process.