Novel Cationic Sulfur Reagents and their Application in Electrophilic Group-Transfer Reactions

by Kai Florian Gustav Averesch
Doctoral thesis
Date of Examination:2019-12-18
Date of issue:2020-06-08
Advisor:Prof. Dr. Manuel Alcarazo
Referee:Prof. Dr. Manuel Alcarazo
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Dietmar Stalke
Referee:Dr. Christian Sindlinger
Persistent Address: http://dx.doi.org/10.53846/goediss-8012

 

 

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Description:NOVEL CATIONIC SULFUR REAGENTS AND THEIR APPLICATION IN ELECTROPHILIC GROUP-TRANSFER REACTIONS

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Abstract

English

The two major research achievements of this work are the development of novel sulfur-based electrophilic transfer reagents based on pyridinium, as well as the extension of the reactivity of already established imidazolium based electrophilic reagents to transition metal catalysis. Both projects share the rationale of electron deficient, nitrogen heterocycles used as backbones, for the polarization of triple bonds to enable new reaction pathways. The synthesis of alkynylthiopyridinium salts, was developed and their reaction with nucleophiles was thioacylation in most cases. The mode of reactivity of these reagents is reminiscent of that of thioketenes. This gave access to dithioesters, thioamides and thionoesters in good to excellent yields under remarkably mild conditions. While for pyridinium based reagents a scope of its reactivity with S-, N- and O-nucleophiles under metal free conditions was investigated, for imidazolium based transfer reagents, a rhodium catalyzed C-H-functionalization protocol with weakly coordinating benzamides was established. A sequence consisting of electrophilic alkynylation of N-methylbenzamides, followed by annulation and finally, hydrolysis of isochromene iminium salts, gave isocoumarins as final products.
Keywords: electrophilic alkynylation; Umpolung; alkynylthioimidazolium salts; alkynylthiopyridinium salts; dithioesters; pyridinium salts; sulfuranes; thioamides; thioketenes; reagents; C-H activation; rhodium catalysis; isocoumarins
 
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