Synthesis and properties of novel iodonium salts

Abstract

Diaryliodonium salts are versatile reagents used for various applications that include electrophilic arylations, building larger cyclic scaffolds, benzyne precursors, and organocatalysis. This thesis presents the synthesis and structural elucidation of novel structures containing two iodonium units in peri-substitution, where a rather repulsive interaction was observed via X-ray crystallography. Furthermore, mixed iodo-iodonium salts were obtained by oxidising only one iodine atom. These were also investigated via X-ray crystallography showing an interaction between the two iodine atoms by coordination of the iodide into the sigma hole of the iodonium salt, resulting in a significantly lowered interatomic distance. In a second project, a continuous multi-step flow procedure was developed for the generation of cyclic diaryliodonium salts from readily available benzyl acetates and alcohols. Combining a Friedel-Crafts step with an anodic oxidation resulted in a method offering a better atom economy combined with a scalable setup. In a third project, cyclic diaryliodonium salts were generated from protected thyroxine. It was possible to generate the corresponding oxidised free thyroxine as well as triiodothyronine. The latter by selective deiodination. The mechanism of this deiodination was investigated via DFT calculations showing resemblance with enzymatic processes with involved halogen bonding. This was also confirmed experimentally as selective coordination to one iodine(I) atom was observed.