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Abstract:
Thianthrenation is a highly selective method to functionalize aromatic C-H-bonds.
Electrophilic activation of a thianthrene-S-oxide in the presence of an arene affords
arylthianthrenium salts. Subsequently, the sulfonium can readily be exchanged for a
variety of valuable functional groups.
Replacing one sulphur atom in thianthrene by a dimethylmethylene bridge affords 9,9-
dimethylthioxanthene. The consequences of this simple modification on the performance
of thioxanthene-S-oxide in the functionalization of arenes, as well as the synthetic utility of the resulting thioxanthenium as synthetic linchpin were investigated in this thesis.
It has been demonstrated that highly electron-rich arenes can be functionalized by using thioxanthene-S-oxide, whereas oxidation of the substrate is a dominant side-reaction of the thianthrenation. However, thioxanthenation of arenes is less site-selective than thianthrenation. The structural similarity of thioxanthene and thianthrene leads to the conclusion that steric effects alone do not sufficiently explain the high para-selectivity of
the thianthrenation.
The exo-cyclic C-S-bond in arylthioxanthenium salts can be selectively cleaved applying transition metal and photoredox catalysis. Further, the reductive C-O-bond formation has been achieved via reductive elimination from S(IV) in arylthioxanthenium salts.
Nevertheless, the functionalization of electron-rich arenes via the reductive elimination of nucleophiles remains challenging. Strategies to solve this problem are presented last.
