From N-Heterocycle-Stabilized Iodanes to novel cyclic Iodonium salts – synthesis, characterization and applications

Abstract

Hypervalent iodine compounds have been established as versatile and environmentally benign reagents for a plethora of oxidative transformations. In this thesis, novel aryl-l3-iodanes substituted by N-heterocycles have been synthesized and investigated towards their structural properties and reactivities. Initially, N-heterocycle-stabilized iodanes (NHIs) based on C- and N-bound azoles have been prepared and successfully applied as highly reactive reagents in oxidative transformations such as sulfoxidations or oxidative dearomatizations. X-ray crystallography confirmed their pseudocyclic, distorted T-shaped structure with strong intramolecular N–I-interactions. Following these stoichiometric reagents, the modification of the arene core to generate catalytically active N-heterocycle-substituted iodoarenes (NHIAs) was investigated. Based on the concept of the hypervalent twist, especially ortho-methoxy derivatives with a benz-oxazole or C-bound triazole as the stabilizing unit proved to be highly efficient organo-catalysts in the a-tosyloxylation of ketones as well as in intramolecular C(sp2)-X couplings. Another priority was the synthesis of novel N-heterocyclic iod(az)olium salts (NHISs). Initially, iodolopyrazolium triflates with various substituents on the pyrazole as well as on the arene core, including derivatives of the pharmaceuticals Celecoxib and CDPPB, were synthesized and their application in diverse derivatizations could be demonstrated. Finally, a range of different iod(az)olium salts based on C- and N-bound diazoles were prepared and investigated as halogen-bond donors, revealing them to be among the most active catalysts known to date.