Fluorine-substituted aryllithiums: basicity, nucleophilicity and synthetic potential
Among other things, the present thesis work aimed at a rational and maximal structure proliferation. Simple arenes or heteroarenes were functionalized regioselectively through organometallic intermediates, which then may be combined with any electrophile to provide attractive new building blocks. The realization of this goal relies on a set of "toolbox methods" and, in particular the modification of the two most prominent permutational methods used for the generation of polar organometallic compounds, the hydrogen/metal and halogen/metal interconversion. Even if in generally only carbon dioxide served as the standard reagent it could be easily replaced by practically any other electrophile. The first objective was to provide a convenient access to a series of new derivatives of 2,2-difluoro-1,3-benzodioxole. After a hydrogen/metal permutational exchange accomplished at the most acidic site, the electrophile was subsequently introduced, affording a series of seventeen first-generation derivatives. Most of them were subsequently converted into second-generation derivatives, thus giving rise to entire populations of new functionalized compounds. The site-selective metalation and subsequent derivatization of selected di- and trifluorophenols was studied next. While it was quite easy to metalate regioexhaustively 2,3,4- and 2,4,5-trifluorophenols by simple mechanism-based substrate/reagent matching, it was more difficult with difluorophenols as they dispose of three vacant sites. The problem could be solved using protecting groups. Thus bulky trimethylsilyl and triisopropylsilyl groups were employed. Alternatively, chlorine enabled the protection of the most acidic position and the same time the activation of neighboring one. The relative carbanion stabilities of typical heterosubstituted aryllithiums in ethereal solution were determined. To this end, the equilibrium was established between phenyllithium and all aryllithiums carrying methoxy, chloro, fluoro, trifluoromethyl and trifluoromethoxy substituents at the ortho-, meta- and para- position by halogen/metal interconversion with the corresponding bromo- or iodoarenes.
Section de chimie et génie chimique
Faculté des sciences de base
Institut des sciences et ingénierie chimiques
Jury: Peter Kündig, Frédéric Leroux, Stefan Pitsch, Thomas Rizzo
Public defense: 2004-9-30
Record created on 2005-03-16, modified on 2016-08-08