Diaryliodonium Salts : Synthesis, Applications and Computational Investigations

Abstract: Organic chemists have the ability to create complex organic molecules by connecting molecular building blocks in different ways. To name a few, these molecules are used as medicines, pesticides or in our household electronics, and are therefore crucial to life as we know it. While many excellent methods for the connection of these fragments are known, serious issues regarding efficiency and sustainability remain. Our research concerns the use of diaryliodonium salts as a way of improving on these issues. Diaryliodonium salts are hypervalent iodine reagents used to transfer aryl groups to suitable nucleophiles. This thesis concerns the synthesis of these reagents and their use in the formation of carbon-nitrogen and carbon-oxygen bonds.The first project investigates the possibility to synthesize unsymmetrical diaryliodonium salts starting from elemental iodine and arenes, as such a method could be more cost efficient and sustainable compared to existing methods starting from iodoarenes. It was found that highly sterically congested diaryliodonium salts could be synthesized in high yields.Next, we applied diaryliodonium salts in the arylation of nitrite to form aromatic nitro compounds. The methodology offered a broad scope with good to excellent yields. Furthermore, we presented the in situ functionalization of diaryliodonium salts that had been formed from iodoarenes and arenes. This conceptually novel approach could be a step towards a catalytic reaction using diaryliodonium salts.In the third project we investigated the mechanisms of O-arylations with diaryliodonium salts to provide a deeper understanding of the reaction pathways involved in product and byproduct formation. Reactions between electron-rich diaryliodonium salts, hydroxides or secondary alcohols were studied.  When using hydroxide as the nucleophile, the side products could be suppressed by the addition of aryne traps, suggesting such an intermediate in the reaction. A novel mechanism for the formation of the aryne was proposed based on DFT calculations.  When alcohols were used we detected the oxidation of the alcohol rather than aryne products. The oxidized product was shown to not originate from arynes or a radical process but was formed via an intramolecular deprotonation from a 4-coordinated intermediate as suggested by DFT-calculations and experiments.In the final project we developed two complementary methods for the synthesis of phenols using hydroxide surrogates as nucleophiles. These compounds have previously been difficult to make using diaryliodonium salts due to aryne formation or overarylation to form diaryl ethers. The first method used hydrogen peroxide as the surrogate and allowed formation of electron-deficient and moderately electron-rich phenols. The synthesis of ortho-alkyl substituted phenols could be accomplished by using silanols as the surrogate. This allowed us to synthesize several highly congested phenols in good yields. Highly electron-rich diaryliodonium salts were, however, not compatible with either of the two methods.